2(1) –1 -1

G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.

PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I

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PART II. SUBSTANTIATION of the AXIOMS PROPOSED in the PART I.

AXIOM 2(1) THE NATURE of ECOSYSTEM STABILITYto PLANT PESTS AND its COMPONENTS

COMPONENTS of ECOSYSTEM STABILITY to PLANT PESTS2.1. PLANT RESISTANCE to PLANT PESTS

The phenomenon of plant resistance to PPs has been known over centuries. The literature abounds in facts concerning this province. The review of such facts has been presented in particular by H. Martin (1928), R. Painter (1951), S.D. Beck (1965), G.E. Russel (1978), F.B. Maxwell and P.R. Jennings (1980).

In the present report, it will be given some examples of subcategories of CESPPs 2.1."Plant resistance to PPs", especially the phenomena, which yet have not been considered as means of plant’s self-protection against PPs. Also, it will be paid attention on potency of CESPPs 2.1. "Plant resistance to PPs”, particularly on capacity of its subcategories to protect plants from the wide range of PPs from voracious large devourers to tiny species of herbivores and all the phytopathogens. These facts allow looking upon CESPPs 2.1. "Plant resistance to PPs" as the main CESPPs in ESPPs, which often cooperates with other categories of CESPPs.

2.1.1. PLANT RESISTANCE to PLANT PESTS OPERATING on the LEVEL of INDIVIDUAL PLANTS

2.1.1.1. Nonpreference

2.1.1.1.1. Nonpreference to herbivores

2.1.1.1.1.1. Nonpreference to herbivores, Visual or tactile

A good example of this subcategory has been provided by. A.V. Zhukovsky (1956, cited in Gorlenko, 1973, pp. 236‑237). It has been found out that varieties of the spring wheat with densely pubescent leaves bear much more eggs of the Hessian fly, Mayetiola destructor Say than the varieties with smooth leaves, especially if the former have weakly expressed furrows. This is so because the contact of an ovipositor with hairs serves as a stimulator for flies’ females. Having no such stimuli, a female often dies before finishing of oviposition. The data of this study conducted in 1952 are shown in the Table 9.

Table 9. Indices of affection of spring wheat varieties by Hessian fly, Mayetiola destructor according to A.V. Zhukovsky (1956, cited in M.V. Gorlenko, 1973, p. 236)

Variety

Rate of leaf pubescence

The number of the eggs per square meter

Percentage of the affected plants

Lyutescence 062

Dense

3168

30.3

Gordeiforme 010

Moderate

520

14.0

Melyanopus 069

Negligible

0

0

In this case, A.2.1.1.1.1.1 "Nonpreference to herbivores, Visual or tactile" serves as the only CESPPs, because the further development of the Hessian fly runs equally on both groups of the varieties. The code of it includes a letter "A", because this is pertinent to articenoses.

The protection of young oat plants in the stage of two leaves against the frit fly, Oscinella frit L. is determined by a width of a split between a stem and a coleoptile (Jonassen, 1980). If the width is greater of some value, frit fly's females lay significantly fewer eggs in the split. This is why in a wide split, the eggs will be rinsed by rains. The split width depends on a variety of the oat.

Further, there is the report, according which a cultivar of the alfalfa is protected against the alfalfa seed chalcid, Bruchophagus roddi Gussakovsky by means the only Nonpreference (probably connected with color of pods), whereas the marks of Antibiosis have not been recorded (Tingly and Nielson, 1975).

2.1.1.1. Nonpreference

2.1.1.1.1. Nonpreference to herbivores

2.1.1.1.1.2. Nonpreference to herbivores, Olphactoral or hustatoral

The studies concerned CESPPs A.2.1.1.1.1.2. are numberless. The efforts have been directed not only on cognition of the plant resistance, but also on search for attractants and repellents for pest insect control. The special attention has been paid to the Colorado potato beetle, Leptinotarsa decemlineata Say. Consider one of such studies, which shows peculiarities of  2.1.1.1.1.2. and its relations with other categories of the plant resistance (Smelyanets et al., 1995). In this study, it was found out four groups of potato cultivars as to their resistance to the pest. The list of the groups with characteristics of pest’s responses and classification of plant resistance according to the present report is the following:

i) Solanum chacoense K‑18892 and K‑7395, full refuse to feed (an operation of CESPPs 2.1.1.1.1.2.).

ii) S. bucasovii K‑9708, S. gourlayi K‑12366, S. parodie K‑2939, S. angustisectuni K‑18159, S. brevicaule K‑5616, S. phyreya P‑52, attractive, but feeding is retarded that leads to high mortality of caged insects at their development {the lack of 2.1.1.1.1.2., but the presence of CESPPs 2.1.1.2.1.2.1. "Antibiosis to herbivores, Physiological (biochemical), Permanent"}.

iii) S. boergeri K‑2920, S. rybinii K‑16533, S. angustisectunii K‑2723, S. saltense K‑5136, S. andigenum K-20519 (var. Imilla negra), S. chacoense K‑9242 and K‑17383, attractive, feeding is active, but insects are spent that leads to significant mortality of the insects (the lack of CESPPs 2.1.1.1.1.2. and CESPPs 2.1.1.2.1.2.1., the presence of CESPPs 2.1.1.2.1.5.1."Antibiosis to herbivores, Nutrient inadequacy of host-plant tissues").

iv) S. bertholtii K‑9702, S. tarijense K‑22015, S. polytrichom K‑8480 and K‑20084, attractive for oviposition, but young larvae die due to the effect of glandular trichomes on a plant surface (the lack all above resistance factors, but the presence of CESPPs 2.1.1.2.1.1.1 "Antibiosis to herbivores, Structural, Permanent").

The lack of attractive and repellent substances in a plant species is also a means of self-protection against herbivores, which should be included in 2.1.1.1.1.2. Here is the report by G. Fraenkel (1969, p. 481): "Leptinotarsa grew almost equally well on the non-solanaceous and non-host-plants Asclepias syriaca and Lactuca sativa as on potato. However, in the choice experiment it greatly preferred potato to these other plants (Table V) (Hsiao & Fraenkel, 1968 c). Very similar experiments were reported by Ritter (1967)."

Because all the subcategories of Antibiosis do not operate in this case, the Nonpreference (2.1.1.1.1.2.) should be considered as the only CESPPs, which provides complete protection of two plant species against such voracious pest as the Colorado potato beetle. Also, these studies have another aspect. They show us that, being forced, herbivores are able to overcome Nonpreference if it is not sustained by Antibiosis. Such situations are common, when herbivore density becomes High.

Thus, the author had a possibility to observe that in the field conditions the cereal aphid, Sitobion avenae Rond. did not colonize several winter wheat cultivars, including Khiroshiri komeigi and Ai-Ai, whereas hundreds others cultivars bore dozens aphids of these species on their spikes. On the other hand, at growing winter wheat in the greenhouse conditions, where density of the aphid reached a thousand individuals per a stem, above-named resistant in the field cultivars also were colonized. Because aphid’s density on them was High, it should suppose that in the field conditions, self-protection of above resistant cultivars is provided by CESPPs A.2.1.1.1.1. "Nonpreference to herbivores", rather than CESPPs A. 2.1.1.2.1. "Antibiosis to herbivores."

2.1.1.1. Nonpreference

2.1.1.1.1. Nonpreference to herbivores

2.1.1.1.1.3. Nonpreference to herbivores, Of unknown nature

Within the diversity of non-preference phenomena, the case of stem borers and their host- plants is rather obscure. Because these insects are very hazardous, the number of studies in this field is vast. However, data of the studies are so contradict one another that this problem should be thought as open one, and referred to as a subcategory of unknown nature (CESPPs 2.1.1.1.1.3.). Consider the some circumstances of vital activity of stem borers and a situation in this field of study. The case of stem borers, especially the bark beetles (Coleoptera: Scolytidae) at a choice by them of foodstuff suitable for development of their brood is an example of an open scientific problem.

The ecological niche of stem borers is limited by host-trees with decreased CESPPs 2.1.1.2.1.2.1."Antibiosis to herbivores, Physiological (biochemical, Permanent." An exception of this rule is observed only at High density of these insects and continues over a short term. Depending of capacity of a stem borer species to overcome residual Antibiosis of host-trees, the rate of this decrease is rather wide - from a complete loss to only a trend to weakening of the Antibiosis. Therefore, it is vitally important for surviving of stem borers to perceive the stimuli connected with their foodstuff (stems of standing host-trees, their branches, twigs, roots close to the soil surface, felled stems, slash, and stumps), and giving information for their populations about suitability of this stuff for colonization. These stimuli allow the borers to avoid dangerous for them effect of antibiotic factors. The absence of such stimuli in host-trees or presence of stimuli of a repellent character should be considered as operation of CESPPs 2.1.1.1.1.3. "Nonpreference to herbivores, Of unknown nature."

For surviving of host-trees, it is beneficial a cooperation of Nonpreference and Antibiosis that is important at expressed aggressiveness of stem borers, when their density becomes High. If physiological state of host-trees has been disturbed, it arises attractive stimuli. They serve as tokens of weakened state of foodstuff for stem borers, i.e.its sutabilility for colonization. The knowledge of nature of these tokens gives a possibility to understand CESPPs 2.1.1.1.1.3. The term "colonization" means establishing of brood by bark beetles in their foodstuff.

In the literature, it has been discussed four patterns of choice by bark beetles (the most studied group of stem borers) of foodstuff suitable for colonization, namely:

v) In flight, i.e. on some distance to a tree.

vi) On a stem surface, i.e. at contact with a tree.

vii) At boring into outer bark, i.e. before a contact with factors of Antibiosis – oleoresin.

viii) At boring into inner (live) bark - phloem contacting with oleoresin.

The first point of view in above list "i" corresponds the concept of primary attraction. Over a long time, it was popular the hypothesis proposed by H.L. Person (1931). According to this scholar, the choice of suitable for colonization by the western pine beetle, Dendroctonus brevicomis Le Conte trees takes place in flight, and the beetles respond on the odor, which occurred to be changed at weakening of trees. Such a view was spread on other species of stem borers by a number of scholars.

The point of view "iv" proposed for the most aggressive species of bark beetles is called "a random attack." This view denies existence of primary attraction and Nonpreference as to species of the group “iv.”

The points of view "ii" and "iii" occupy the intermediate position between above extremes. Consider the experimental data in this field.

Here is the study by D.L. Wood (1974). Sticky traps exposed on stems of healthy host-trees, obviously weakened host-trees and nonhost-trees showed the same landing rate of bark beetles Dendroctonus brevicomis and D. ponderosae Hopk. These results contradict the point of view "i" and leave the validity of "ii", "iii", and "iv" to be open.

J.S. Elkinton and D.L. Wood (1980) found out the same landing rate and gallery initiation of Ips paraconfusus Lanier on host-trees (Pinus ponderosa Laws.) and nonhost-trees (Abies concolor Lindl.). The preference for the pine over the fir took place in the phloem that was shown by laboratory bioassays with the ground and nonground tissues. These findings are consistent with the point of view "iii." The further development of this view is presented in the article by J.S. Elkinton et al.(1981).

G.B. Hynum and A.A. Berryman (1980) observed the same landing rate of Dendroctonus ponderosae on stems of living and dead host-trees and nonhost-trees. Within living host-trees, the number of gallery initiation was greater on trees with higher content in outer bark beta-phellandrene. This trend was weak although veracious one. Thus, the study gives some grounds for validity of the point of view "iii.”

For Dendroctonus frontalis Zimm., the similar results were obtained in a laboratory bioassay by J.D. White (1981). In outer and inner bark of Pinus taeda L., it was found out gustatory attractants and repellents. Their ratio was thought to be the main stimulus in a choice of suitable for colonization trees. The gallery initiation was considered as random one.

The most clearly, the concept of random attack (the point of view "iv") was expressed by K.F. Raffa and A.A. Berryman (1983) on the base of interactions of Dendroctonus ponderosae and its host-tree Pinus contorta var. latifolia Engelm. The beetles attacked host-trees without discrimination them as to their physiological state. The success of attacks depended exclusively on density of attacking beetles. If the density was less 40 beetles per square meter, they were not able to overcome resistance of a tree (oleoresin exudation), a tree survived, and beetle's brood died. The higher density lead to successful colonization (probably of quite healthy trees). Such an understanding of the interrelations needs not in presence any attractants or repellents in host-tree bark.

In the article by D.L. Wood et al. (1986), which summarizes 25-years studies, this view has been spread also on Dendroctonus brevicomis and Ips paraconfusus. Being in the range of activity of attractive pheromone, beetles of the latter species elated on nonhost-tree species Abies concolor Lindl. and penetrated in its phloem, but eventually left it. It seemed that choice of discrimination of host-trees and nonhost-trees took place at contact with gustatory stimulators in phloem. Tests with extracts of phloem showed positive response on the latter and negative one on the former.

Ja. Witanachchi and F.D. Morgan (1981) reported that healthy and weakened trees of Pinus radiata were attacked by the same number of innumerous beetles of Ips grandicollis Eichhoff that showed an operation of random attack.

The second line of data gives evidences in favor of operation of the primary attraction (the point of view "i").

Window-barrier traps attached on fire-scarred and unscarred host-trees showed the significantly greater response of Dendroctonus ponderosae to the former (Gara et al., 1984).

The data on Dendroctonus frontalis are contradictory. This species is able to form vast infestation spots embracing hundreds or thousands pines indiscriminately. It seems this fact gives evidence in favor of operation of random attack. However, such outbreaks arose in overstocked monocultures planted on old-field lands, where all the trees were weakened due to competition. On the other hand, in natural pine stands, colonization by Dendroctonus frontalis was limited by innumerous and scattered weakened trees – the annual stem fall of a stand and occasionally weakened trees (Showalter et al., 1981). These observations are hardly to be understood from the view of random attack.

In the experiments, host-trees of Dendroctonus frontalis severed and installed vertically were not colonized by this species (Gara et al., 1965). This fact might be explained by attraction of the beetles by stem's billets with recent attacks of the beetles situated near by. True, in the article by G.C. Gaumer and R.I. Gara (1967), it was reported that severing of the main stems was failed to attract Dendroctonus frontalis, when near by pines were being attacked during an outbreak. Further, R.I. Gara et al. (1965) reported that at Low density of Dendroctonus frontalis, its colonization was limited by weakened standing trees, windthrown trees, and even slash. It is difficult to explain this fact, if the primary attraction does not exist.

There is a study that poses Dendroctonus frontalis in a raw of the "secondary" bark beetles, which are attracted by trees in expressed weakened state and colonize them (Heikkenen, 1977). In this study, thousands of the beetles were collected in traps on stems of severed and remained in vertical position host-trees, whereas healthy trees and less weakened (girdled) trees attracted a few beetles of Dendroctonus frontalis.

In this article as well as in other one (Hines and Heikkenen, 1977), it was reported that the severed trees attracted many beetles of stem bores of the genera Ips, Hylastes, Xyleborus, Monochamus, Hylobius and Cossonus.

D.R. Miller et al. (1986) reported about the primary attraction for Ips latidens and Hylastes gracilis.

The study of R.N. Coulson et. al., 1986) denies operation of random attack in the whole the southern pine bark beetle guild. In it, trees of the loblolly pine, Pinus taeda were artificially damaged ("disturbed") that simulated affection by lightning. The bark beetle guild, including Dendroctonus frontalis, D. terebrance Olivier, Ips calligraphus Germar, I. grandicollis Eichhoff, and I. avulsus Eichhoff begun their colonization with disturbed trees scattered within a stand. In a result "All the disturbed hosts were discovered and colonized by the bark beetle guild. Multiple –tree infestations developed from 10 of 20 treatment centers" (Ibid., p. 859). Hence, it was selected weakened trees, whereas the colonization without discrimination of host’s physiological state was possible under effect of secondary attraction.

With the aim to elucidate this confused problem, it should turn attention to the idea by J.P. Vite and G.B. Pitman (1968) about the fundamental difference between characteristics of aggregation on host-trees in the genera Dendroctonus and Ips. These scholars stressed that several Dendroctonus species, especially Dendroctonus frontals, D. brevicomis and D. ponderosae, have a trait to produce "contact" pheromones, when attacking of host-trees. In combination with odor of terpenoids of oleoresin, which exudes from initial attacks, these pheromones have an ability to increase greatly positive response of the rest of beetles. In a result of such a synergism, it arises the "mass attack", which allows the beetles to colonize successfully quite healthy trees. Their antibiotic response is overcome by boring of numerous beetles. Importantly, successful colonization occurs on condition that large amount of a beetle population that provides High density of the attacks. If the amount is little, attacking beetles cannot overcome the antibiotic response of attacked trees, and the beetles are forced to leave them.

In a contrast to the above-mentioned Dendroctonus species, in the genus Ips, beetles of a host-finding sex (males) have highly sensitive capacity to perceive stimuli of primary attraction. Therefore, they are able to select appropriate for colonization material with decreased Antibiosis – stems of trees, tree-tops, branches, and slash.

There are a number of facts that give evidence in favor of validity of the concept by J.P. Vite and G.B. Pitman (1968). The Dendroctonus species have a sloping hinder part of their elytrae. This trait is convincing for clearing out of a body from oleoresin at attacking of host-trees, but it is not convenient for clearing out of egg galleries from frass. Contrary, the Ips species have a special structure in a hinder part of elytrae, which in the Russian literature is called "a barrow." It allows junk easily frass from egg galleries, but in stems with significant oleoresin exudation, such a structure is filled by this product that disables the beetles by mobility and leads to mortality of them. Therefore, to find weakened trees is of greater importance for the Ips species than that for the Dendroctonus species.

For Ips grandicollis Eichhoff, the data on absence of a "contact" pheromone have been obtained by J.P. Witanachchi and F.D. Morgan (1981). In these studies, exposition of the aggregation pheromone (ipsenol) on weakened trees induced much greater attraction than that on healthy trees. This fact was explained by obstacles for pheromone producing by oleoresin exudation on healthy trees. "…beetles boring into resistant trees do not produce ipsenol" (Ibid., p. 222).

Ips typographus beetles also are unable to produce "contact" pheromone. In the studies by G.I. Vasechko (1978a), it was collected a mixture of oleoresin and boring dust, which had been pushed out on a stem surface by pioneer male beetles of this species. Testing of this mixture in a laboratory olphactometer showed an absence of attractiveness of this mixture for walking beetles. Importantly, the number of the attacking beetles reached hundreds per tree. Neither on this tree, nor on adjacent trees, sources of a pheromone (frass of successfully colonized beetles) were present. Therefore, this was a mass attack without the secondary (pheromonal) attraction.

Also, these bioassays showed that the beetles, which had contact with host-tree oleoresin, were not attractive, whereas the beetles having no such a contact were just attractive. These finding differ to those for the "primary" Dendroctonus species.

The data of this discourse suggest that the “primary" Dendroctonus species are able to select weakened trees (with decreased oleoresin exudation). Nevertheless, the beetles prefer trees with significant oleoresin exudation, whereas the colonization of weakened trees occurs, when amount of a beetle’s population is insufficient for overcoming of antibiotic response of rather healthy ones.

What is a cause of the preference of trees with significant oleoresin exudation? The colonization of such trees allows them to avoid a competition on the part of the Ips species. The latter are more successful competitors than the former. This fact has been shown by L.J. Ravkin and J.H. Borden (1990) on the example of Dendroconus ponderosae and Ips pini Say. In the laboratory experiments conducted by these scholars, a simultaneous attack of the both species resulted in a decrease of Dendroctonus ponderosae brood up to 96.2 %. An attraction of the Ips species with pheromones to trees colonized by the Dendroctonus species even has been recommended for suppression of the latter.

The attempts to avoid the competition with the Ips species fraught with serious consequences for the Dendroctonus species. When amount of their population is great, they are able to overcome antibiotic response of actually healthy trees. But High density of their attacks that is necessary for successful colonization results in big decrease of their brood due to an intraspecific competition. K.F. Raffa and A.A. Berryman (1983) showed that the attack density of Dendroctonus ponderosae over 80 galleries per square meter provided full success in suppression of antibiotic response of Pinus contorta var. latifolia Engelm., but a decrease of the brood occurred to be significant due to lower fecundity and drying of phloem. On the other hand, attack density less 40 galleries per square meter was insufficient for suppression of host-tree Antibiosis, and the brood died.

Moreover, it was observed that trees are able to stop an attack of the Dendroctonus species in its beginning (Linit and Stephen, 1982). Although in that case, it is not clear the cause of such a stopping – a developed capacity of host-trees to protect themselves (some special "physical" properties of oleoresin as the scholars suppose) or simply the limited number of the beetles in their population that does not allow them to aggregate en masse.

Within the Dendroctonus genus, there are three species, which differ significantly as to the question under consideration from the "primary" species, and they have some common features. They are the black turpentine beetle, Dendroctonus terebrance Oliver, the red turpentine beetle, Dendroctonus valens Le Conte, the European spruce beetle, Dendroctonus micans Kug. The large number of beetles of these species are attracted by odor of oleoresin, turpentine, and divers monoterpenes. This was stated by case observations and field experiments for Dendroctonus terebrance and D. valens (for original data and a review of literature see C.W. Fatzinger, 1985), and in the laboratory experiments for Dendroctonus micans (Vasechko, 1988).

The positive response on the odor related to oleoresin might be explained by the fact that initial ecological niche of these species is limited by a low part of a tree stem and large roots close to the soil surface. These tree parts often are damaged, and odor of oleoresinous substances serves as a token of wounds. Near by wounds, phloem has weakened Antibiosis that is favorable for successful colonization by beetles of this group. Attacks of these species are usually accompanied by "pitch tubes" – masses of oleoresin, which are pushed out on a stem surface by the beetles. They do this with the aim further weakening of phloem that it is necessary for survivorship of their brood to adulthood. Although beetles of these species possess by developed tolerance to oleoresin, their larvae are susceptible to oleoresin nearly as those in the rest of bark beetle species, which are able to colonize living trees.

The attacks of tree parts with significant oleoresin exudation should not be considered as inability of a bark beetle species to select weakened foodstuff. It should consider such cases as the situations, when beetles are forced to do this, because shortage of more favorable foodstuff. When Dendroctonus micans is able to make a choice, its beetles attack standing trees selecting weakened ones independently to presence of stem wounds. Such a behavior of Dendroctonus micans is common in the Borzhomi Valley (Georgia, the Former Soviet Union). This is an evidence that D. micans is able to perceive stimuli of primary attraction.

What kind of stimuli might compose primary attraction? First of all, they might be olphactory stimuli. Significant information about this field has been presented in the article by D. Klimetzek et al. (1986). On the base of own experiments and a review of literature, the scholars categorize all the diversity of bark beetle species and some other stem borers according to their responses to traps with the following lures: ethanol, terpenoids, phloem of host-trees, and pheromones. A distribution of species taking into account their responses to combinations of above lures composed five groups is as follows:

ix) Ethanol is the main stimulus of attraction, such species colonize foodstuff with advanced deterioration, they are indifferent to specific affiliation of the foodstuff (Xylosandrus germanus Bland., Hylecoedes desmestiodes L., the family Dermestidae).

x) Ethanol is a synergist of a host-tree odor, the species close to the group “i” but more fastidious as to specific affiliation of the stuff (Hylugrops palliatus Gyll., Hylastes spp.).

xi) Ethanol is a synergist of a host-tree odor and a pheromone odor (Drycoetus autographus Ratz., Trypodendron spp., Gnathotrichus spp.).

xii) Ethanol is a synergist of attractive pheromone and/or host-tree odor, the moderately aggressive species (Lesperesinus varius F., Blastophagus=Tomicus spp., Dendroctonus terebrance, D. valens, D. pseudotsugae).

xiii) Ethanol does not connected with the stimuli of attraction, and decreases attraction at participation in a lure, the most aggressive species colonizing healthy trees (Dendroctonus frontalis, and Ips typographus ).

An analysis of this classification allows to draw some conclusions as to stimuli of primary attraction and to propose some corrections.

In the groups "i, ii, iii" (they might be united by the term "tertiary" species), which in their preferences are limited by dead wood, the role of host odor is significant. As a token of suitability of hoststuff of the wide range of tree species, it serves ethanol appearing at decomposition of wood tissues.

In the group "iv", which need weakened, but living trees ("secondary" species), the role of host odor in responses on the significant distance from host-trees is low, if any.

In the group "v" ("primary" species), beetles are able to colonize host-trees, which is close to healthy state. Neither host odor, nor ethanol plays a significant role at attraction on some distance to host trees.

In the present report, there are no propositions as to the groups "i", "ii", "iii", whereas in the groups "iv" and "v", it seems to be useful some rearrangements and specifications.

Let the group "iv" includes the genera – Ips, Orthotomicus, Pityogenes, Pytiokteines, which prefer for colonization weakened, but fresh foodstuff. Although at high amount of their populations, many of species within the above genera colonize successfully healthy trees near by weakened ones. In so doing, the beetles aggregate responding to pheromones, which are produced by the beetles colonizing weakened trees. In this group, colonization of host-trees by random attack is of a little probability.

The group "v" is limited by three Dendroctonus species – Dendroctonus terebrance, D. valens and D. micans. It is characteristic for host colonization by them, the expressed preference to objects with significant oleoresin exudation – areas around wounds on living trees or fresh stumps. Appearing of "pitch tubes" at attacks of these species is a common event. The tubes are composed by oleoresin and particles of phloem (boring dust), which pushed out by attacking beetles that reflects a significant level of protective response of a host-tree. Dendroctonus micans has no aggregation pheromone (Vasechko, 1978a). These species select suitable for colonization objects responding to stimuli in flight, and odor of host-trees plays a significant role among them. "Dendroctonus valens, the red turpentine-beetle, and Dendroctonus terebrans, the black turpentine-beetle, are almost always secondary" (Graham, 1939, p. 232). Dendroctonus micans is secondary always, having no possibility to colonize healthy parts of trees (Vasechko, 1968).

The group "vi" embraces the most aggressive bark beetle species – Dendroctonus frontalis, D. ponderosae, and D. brevicomis, which are able to colonize host-trees independently on their physiological state on condition that an amount of their populations is great. This is a colonization by "random attack." In healthy trees, they reach success due to a capacity to produce "contact" (aggregation) pheromones, whose attractiveness increases in combination with odor of oleoresin exuded from attacking trees. When amount of their populations is little, they are forced to select weakened trees. Let they be "primary" Dendroctonus species.

The available information as to bark beetles of the groups "iv", and "vi" is insufficient to draw conclusion as to the stimuli, which bark beetles percept at foodstuff finding.

Some speculations might be proposed for explanation of the shift in behavior of the group "vi" depending on amount of their populations. According to the first idea, the beetles attack host-trees at random independently on amount of their populations. When the amount is little, they forced to leave attacked trees if they are healthy, and search for weakened ones, because pioneer beetles do not have support at attacks.

The second idea consists in a capacity of the flying beetles to perceive the concentration of pheromones in air within an ecosystem. If this concentration is low, they switch on search for weakened trees. In an opposite situation, they practice random attack. This idea is based on the fact of a presence in hindguts of the beetles a pheromone before attacks, in particular in unfed females of Dendroctonus ponderosae (Libbey et al., 1985). In addition, the species of this group begin colonization three to five days after a start of a flight period that suggests their capacity to evaluate the situation in an ecosystem during this period. Moreover, "…there is some evidence to suggest that pheromones may have a residual life of at least one year" (Wood, 1982, p. 414).

In all the above patterns of the choice of foodstuff, bark beetles must contact with odor or taste of host tissues. It is logical to search for the host substances, whose composition changes at weakening of trees and explain the choice by this change. There exists a wide spread view that the choice of foodstuff is determined by changing in an odorous fraction of oleoresin - turpentine due to weakening of trees. The changes might be of two ways – an appearing of new components or disturbance in a ratio of components comparing with that in healthy trees.

Consider the studies conducted with the aim to reveal the dependence of turpentine composition on physiological state of trees in the context of colonization of them by bark beetles.

P. Miller et al. (1968) noted the preferred colonization by Dendroctonus ponderosae and Dendroctonus brevicomis the trees of Pinis contorta var. latifolia Engelm. affected by photooxidant injury, and studied a composition of turpentine in healthy and affected by the injury trees. The data of this study are presented in the Table 10.

Table 10. Composition of turpentine in stem oleoresin of Pinus ponderosa depending on physiological state of trees in stands affected by photooxidant injury

Physiological state of trees

Content of monoterpenes in turpentine, percents

Alpha-pinene

Beta-pinene

Delta-3-carene

Mircene

Limonene

Fellandrene

1

2

3

4

5

6

7

Healthy: a) average

b) the range

10.3

7-10

50.3

37-60

Traces

—

11.2

2-19

27.4

20-39

1.6

1.1-2.0

1

2

3

4

5

6

7

Diseased

a) average

b) the range

9.5

7-16

49.4

33-65

Traces

—

10.0

2-18

29.3

13-44

0.9

0.1-2.0

The difference in the content of these substances in the healthy and diseased trees occurred to be invalid.

The effect of a composition of a solid fraction of oleoresin – the colophone at the choice of foodstuff is of little probability. Nevertheless, as to this phenomenon, the healthy and diseased trees were indiscernible (Miller et al., 1968).

The vast studies of composition of turpentine of the Siberian larch, Larix sibirica L. in the context of the problem under study for Ips subelongatus Motsch. and other species of stem borers were conducted by A.S. Isaev and G.I. Girs (1975). The extraction from the tables of this publication is shown in the Table 11 (cited according to G.I. Vasechko, 1981a, p. 23).

Table 11. Composition of turpentine and content of this product in phloem in stems of the Siberian larch, Larix sibirica on the height 1.3 meter above the soil surface depending on attraction of Ips subelongatus. The extraction from A.S. Isaev and G.I. Girs (1975, Table 14, p. 124, and Table 25, pp. 140‑141)

Substances

Trees unattractive for stem borers in a butt portion of a stem

A tree on a limit of attracti-on (with rebuffed attacks)

Trees defoliated by Dendrolimus sibiricus and colonized by Ips subelongatus. The increase in numbers corresponds the level in development of the brood

A healthy tree

Defoliated by Dendrolimus sibiricus

Without attacks

A tree colonized in a top portion

1

2

1

2

3

1

2

3

4

5

6

7

8

9

Alpha-pinene

34.0

47.44

40.56

51.50

50.02

45.75

39.71

29.96

Beta-pinene

18.0

21.14

25.50

21.60

25.67

21.75

18.71

16.64

Delta-3-carene

28.0

23.31

17.69

15.80

10.30

22.13

36.79

39.63

Alpha-phellandrene

No data

—

4.81

—

3.01

—

—

5.07

Linonene and dipentene

9.0

6.23

3.98

8.70

2.97

8.24

2.89

3.58

Beta-phellandrene

0.3

Traces

7.44

1.30

8.02

1.27

1.19

5.11

Terpinolene

0.5

1.85

0

0.80

0

0.82

0.68

—

Others

10.2

0.03

0.02

0.30

0.01

0.04

0.03

0.01

Content of turpentine in phloem, percents on dry weight

0.08

0.05

0.05

0.09

0.07

0.09

0.17

0.08

Although mathematical treatment of the data showed in the Table 11 was not done, the data embraced the wide range of variants and demonstrated an absence on the dependence of Ips subelongatus attraction on composition of turpentine and content of turpentine in host-tree phloem.

In the cited book of A.S. Isaev and G.I. Girs (1975), one may find the data on attraction of Ips subelongatus for middle and upper parts of stems. As to these stem parts, the conclusion is analogous – the dependence of the attraction on turpentine composition ant its content is absent. These indices fluctuate in the wide range independently to physiological state of larch trees.

The author of this report has a possibility to present own data on the composition of turpentine in the Norway spruce, Picea excelsa (abies) (L.) Link. depending on physiological state of the trees. These samples for study of composition of turpentine (oleoresin or phloem) were taken in spring on felled trees immediately before attacks of them by Ips typographus and its satellites – Ips amitinus Eichh., Pytiogenes chalcographus L. and other stem borers. In the same time, the samples were taken on standing trees. The standing trees were unattractive and quite resistant against all the stem borers. The latter was proved by artificial setting of Ips typographus beetles, which were unable to colonize the trees being expelled by oleoresin exudation. Physiological state of the trees was considered as good, if they are unable to be colonized by bark beetles, and as weak one in the case of successful colonization. Also, the samples of were taken in areas of colonization by Dendroctonus micans and stem wounds free from attacks of this species. The obtained data are presented in the Table 12.

The dispersion analysis of these data presented in the Table 13 has shown that the role of a source of terpenoids as a factor of the dispersion is low (only 8 %). This is an evidence of a lack of effect of physiological state of a tree on composition of its turpentine. The organized factors (the difference in content of separate terpenoids and the unidentified rest formed 86 % of the dispersion, and the sources of terpenoids formed 8 % of the dispersion). The most part of the effect, i.e. 94%, was formed by the organized factors. This is a sign of validity of the study’s results. The unidentified rest consists of thirty-five substances. Their chemical structure was not identified. Nevertheless, it was not noted the dependence of their content on physiological state of a tree. Because the factorial "F" is greater than the theoretical "F", results of the studied are valid.

The lack of differences in the composition of turpentine in phloem of healthy trees, weakened trees, in oleoresin in stem wounds and attacks of Dendroctonus micans allows to draw a conclusion that composition of turpentine is not connected with the patterns of choice by bark beetles of foodstuff for colonization as to the spruce bark beetles Ips typographus, Dendroctonus micans, and their satellites.

The data of the Tables 12 are in concordance with the studies of composition of turpentine, which was conducted without a connection with the problem of the choice by bark beetles of host stuff for colonization. A number of scholars noted a variation of the composition in the wide range in trees of roughly the same physiological state, although the composition was characteristic for a tree species. Such data might be found in the reports of I. Bardyshev et al. (1950), I. Bardyshev (1952), N.T. Mirov (1958), R.H. Smith (1964), S. Juvonen (1966).

Table 12. Composition of turpentine in oleoresin of Picea excelsa (abies) of diverse sources, percents

Substances

Healthy trees, phloem, the number of trees

Felled and attacked by bark beetles trees, phloem, the number of trees

Oleoresin from wounds on stems, the number of wound samples

Oleoresin from attacks of Dendroctonus micans, the number of samples

1

2

3

1

2

3

1

2

1

2

1

2

3

4

5

6

7

8

9

10

11

Santene

0

0

0

0

1.6

0.7

0

0

0

0

Alpha-pinene

39.8

42.5

25.1

26.1

22.6

26.1

31.6

31.6

33.1

13.1

Camphene

1.3

3.2

2.3

3.3

4.3

3.7

1.8

1.0

2.6

0.9

Betha-pinene

39.8

21.2

37.3

31.6

31.1

31.7

40.4

26.6

28.4

30.6

Deltha-3-carene

3.8

7.9

8.1

7.1

9.7

7.2

3.4

21.0

19.8

27.2

Limonene

0.4

0.4

0.4

0.6

0.5

0.4

0.4

1.1

0.6

1.4

Gamma-terpinolene

0

0

0.3

0

0.3

0

0

0.5

0.3

0.9

P-tsimole

2.7

10.1

3.8

4.7

4.0

4.1.

7.3

7.3

0.5

5.2

Terpinolene

6.7

3.2

16.3

10.1

11.8

6.0

5.3

3.8

4.9

7.1

Bornil-acetate

0

0.1

0.2

2.5

0.3

0.4

0.5

0.4

0.2

0

Borneol

0.2

0.5

0.1

0.1

0.3

0.4

0.3

0.1

0

0

An unidentified rest

5.3

10,9

6.1

13.9

13.5

19.3

9.0

6.6

9.6

9.1

Total

100

100

100

100

100

100

100

100

100

100

Table 13. The results of dispersion analysis of the data of the Table 12

A category of dispersion

Values of dispersion

The number of degrees of freedom

A ratio of dispersion(factual "F")

Theoretical "F"for P= 99.99%

Absolute ciphers

Percents

V1

V2

Total

15744

100

—

—

—

—

Among separate terpenoids and the rest

13557

86

11

72

93.9

3.4

Among source of turpentine

1286

8

33

—

3.0

2.5

Random

941

6

47

—

24.1

2.5

It was proved the effect of a hereditary factors and age of tree tissue on the turpentine composition (Mirov, 1958; Pigulevsky, 1961, cited in L.A. Ivanov, 1961, pp. 57-58; Poltavchenko et al., 1968). However, environmental conditions, whose impact on physiological state of trees was obvious, did not exert an effect on the composition (Krestinsky et al., 1932; Hanover, 1966). The wide diversity of the turpentine composition within a host-tree species independently on physiological state of such trees queries the hypothesis of the significant role of turpentine odor in the patterns of choice by bark beetles of foodstuff for colonization.

The data of laboratory and field experiments on attractiveness of turpenoids are contradictory and give no grounds for valid conclusions as to presence of attractants and repellents (for review see G.I. Vasechko, 1978, 1981, 1988). Moreover, bark beetles demonstrate a surprising positive response to xenic substances. For example, J.A. Chapman (1963) reported about aggregation of 4268 individuals of the bark beetle Dolurgus pumilis Mann. and 63 beetles of Hylastes sp. in a barrel with a rest of solution of the insecticide BHC in mineral oil.

Because the attempts to explain the choice by bark beetles of foodstuff for colonization by olphactory stimuli in the groups "iv", "v" and "vi" is a matter of difficulty, it should pay attention on visual stimuli. The data in this field are abundant. The review of them have been given in particular in the reports by G.I. Vasechko (1974, 1978a, 1981a, 1988).

It occurred to be that a position of stems (vertical or horizontal) and color of objects simulating a stem exert a potent effect on attraction of bark beetles. The species, which at the colonization in natural conditions give preference to standing trees, prefer vertical objects in experiments. They are Dendroctonus valens, D. frontalis, and D. ponderosae. The position of an object is so important that in vicinity of billets of host-trees with new attacks of Dendroctonus frontalis (they have been cut from standing attacked trees), beetles of this species bore into bark of standing trees, including non-host (deciduous) species and ignore the billets (Gara et al., 1965).

The species of the genera Ips, Trypodendron and Dendroctonus brevicomis colonizing indiscriminately standing and laying stems do not demonstrate a difference in the position of objects, when respond in experiments. Orthotomicus proximus Eichh., which colonize only laying stems, ignores cut and put vertically pine stems (D.F. Rudnev, pers. comm.).

A number of publications pays attention on the fact that temperature of a stem surface of felled or weakened standing trees is higher comparing with that in healthy ones. In a result, the former becomes contrastive in the infra red range. Such an irradiation of weakened host-trees is thought to be a stimulus of attraction for Melanophila accuminata De Geer (the family Buprestidae), Monochamus galloprovincialis Ol. (the family Cerambycidae), and some species of bark beetles.

Olphactory stimuli have some significance in the choice of foodstuff. The tests with exposition of wire cylinders, their attractiveness for Ips typographus became a little higher, when a billet of host-tree was sheathed in a cylinder (Vasechko, 1978a). However, the role of host odor was surprisingly low.

In this context, it is important that near by a potent source of secondary attraction (odor of an aggregation pheromone), bark beetles bore in bark of nonhost-trees (Gara et al., 1965). Of course, such beetles soon leave them.

The tokens of weakened state of foodstuff operating over the short-distant range (on a stem surface) are unknown. It is prospective to search for them among phenomena of the acoustical nature. The matter of fact, in stem’s tracheids, i.e. tubes of a capilliar diameter, it takes place the physical phenomenon of the adhesion. According to divers evaluations, the adhesion develops the lifting capacity from tens to hundreds of atmospheres (Kramer and Kozlowsky, 1960, Ch. 11). It allows transporting moisture from roots of a tree to its top on the distance more hundred meters. Importantly, the transportation occurs in the state of uninterrupted threads. At weakening of trees, this process becomes broken, and the threads undergo numerous disruptions. The sounds arising at the disruptions might be perceived by stem borers on a stem surface, and used by them for choice of the foodstuff suitable for colonization.

In conclusion, it will be proposed some suggestions as to a sequence of stimuli at host finding in a number groups of bark beetles with an attempt to find a compromise over a diversity of the contradictory data.

Let us begin with a scenario for the group "iv." The typical species is Ips typographus. The pioneer beetles (males) respond positively on objects of a cylindrical form in vertical of horizontal positions similar to stems of their host-trees – the spruce. In so doing, the preference is given to those objects, which stand out a background (the main stock of host-trees) being warmer. Increased temperature of a stem surface serves as a rough token of weakened state of host-trees. This token is a rough, because the increase of stem temperature is possible in dead host-trees or in nonhost-trees. It might be, such trees differs in their shining in the infrared range.

The next step of the choice takes place on a stem surface. Here, the pioneer beetles discriminate host-trees from nonhost ones by odor, whereas a weakened state of trees is proceeded by perception of sounds of tracheid disruptions and/or other unclear stimuli. In the case of recognition of suitability of such an object for colonization, they begin to bore outer bark and penetrate into phloem. If the antibiotic response in an attacked tree is absent, the beetles produce an aggregation pheromone, which attract mainly females. Responding to the odor, females leave their shelters, for example forest litter, where this species hibernates. The secondary attraction continues until an anti-aggregation pheromone begins to be produced, i.e. when fecundation terminates.

If the antibiotic response still retains, the beetles continue boring activity producing no a pheromone. It occurs a mass attack of males induced by stimuli of primary attraction. Wounding of phloem by the boring causes a drip out of oleoresin on a stem surface that weakens an attacked tree. If amount of a bark beetle population is sufficient to overcome host-tree self-protection, it begins a producing of a pheromone, which attracts mainly females of this species.

When weakened host-trees are in shortage, in beginning of flight period of Ips typographus only males of this species are active. They suppress protective response of their host-trees without producing of the pheromone. If in that time to expose dispensers with the pheromone, one may observe how the females creep out forest litter, and rise on stems of any trees, where the dispensers are exposed. The “barrow” on a hind part of their elytrae is covered by clay. This is an evidence that the females else do not fly, and they percieve pheromone odour staying in the shelter, i.e. in forest litter.

The females penetrate in entrance holes on parts of the stems with suppressed oleoresin exudation, whereas the attracted males continue to bore in those stem parts, where oleoresin exudation still is not suppressed. The males are attracted by the pheromone also, although they tend to attack uncolonized parts of trees and near by trees. Thus, in Ips typographus, the pheromone serves both as a sex attractant and aggregative one (Vasechko, 1978a).

The group "vi" - Dendroctonus frontalis, D. brevicomis, D. ponderosa. The first scenario is the following. Over several days in the beginning of a flight period, the beetles do not attack host objects. They release an aggregation pheromone and perceive concentration of its odor in air. If its concentration exceeds some threshold, some beetles (pioneers) take the initiative to colonize any standing tree. Dendroctonus ponderosae, it seems, is indifferent to the direction of a stem. Some preference is given to more heated stems, that might be sign of weakened state of them.

In fact, "Studies of landing rates of …(Dendroctonus brevicomis) on host, non-host, and hosts dead for one year in California showed an elevated catch on the dead trees…" (Wood, 1982, p. 414). Stems of dead trees are more heated than those of living trees. A discrimination between host and nonhost-trees takes place on a stem surface. The pioneers do not perceive the intensity of antibiotic response and do not select trees with higher oleoresin exudation. The preference of the trees with intensive oleoresin exudation is probable at a large amount of a population. The expressed antibiotic response does not preclude a success of colonization, but the brood obtains an advantage in competition with Ips species. The synergism of odors of contact pheromones and oleoresin at its abundant exudation causes a mass attack that allows to overcome host-tree Antibiosis of any its rate. In contrast to the group "iv", mortality of beetles in above-mentioned Dendroctonus species at mass attack is low due to structures of their bodies.

When the concentration of pheromonal odor in air is below some threshold, the beetles are forced to search for weakened foodstuff –the annual stem fall, and the trees struck by lightning, windfall, and slash. The tokens of weakened state of foodstuff might be the same as in bark beetles of the group "iv" – increased temperature of bark, sounds of tracheid disruption or others. A lack of these tokens might be used by the pioneers at colonization of healthy host-trees, when an amount of a population is great, and threfore weakened foodstuff are less preferable.

According to the second scenario, which seems to be less probable, pioneer beetles elite on stems of trees at random, discriminate host and non-host trees on a stem surface responding on food stimulants in the former, and bore into phloem of host-trees independently on the rate of their antibiotic response. If this response is so active that producing of contact pheromone is impossible, the are forced to search for weakened foodstuff. In so doing, the use the tokens, which have been suggested above.

The group "v" - Dendroctonus valens, D. terebrance, D. micans. In this group, as a rough token of suitability of foodstuff, it serves odor of oleoresin. This is so because the odor accompanies of wounds in butts, roots close to the soil surface, and stumps. Areas of phloem around of wounds make up an ecological niche of these species. Visual stimuli connected with vertical objects also play a significant role at the first stage of foodstuff finding. An exact choice of areas suitable for development of brood is proceeded in phloem. If oleoresin exudation still retains, parental beetles condition the media pushing out oleoresin on a stem surface. Pitch tubes are common at attacks by these species.

The groups "i", "ii", and "iii". Because beetles of these groups use for colonization foodstuff with signs of tissue decomposition, it is probable at host finding a positive response in flight to volatile substances accompanied this process. Attraction by ethanol is evidence in favor of this suggestion. At boring into phloem, the beetles testify the suitability of the media as to humidity and freshness of tissues.

At foodstuff finding, it is used divers patterns of perception of stimuli of it. In all the above groups, the first step in the sequence is positive response in flight (the group "i") on objects resembling tree stems in favorite position – vertical, horizontal or in any position. Shining of stems in the infrared range as a probable token of weakened state of host-trees of the group "iv" also is perceived in flight. Dendroctonus terebrance is attracted in flight by host odor. On a stem surface, the beetles discriminate host-trees from nonhost ones by odor, evaluate physiological state of trees by acoustical stimuli, and freshness of phloem again by odor (the group "ii") in all the groups, except "v." In the latter, the recognition takes place in phloem (the group "iv").

Above studies of foodstuff finding by bark beetles give grounds to suppose that contrary the idea of random attack, CESPPs of the category 2.1.1.1.1.3. “”Nonpreference to herbivores, Of unknown nature” indeed operates, and it is provided by absence of stimuli for colonization by these insects, or the stimuli have repelling character, and diverse nature. It is well-expressed the role of the prerequisite 2.1.1.P.2. “The proper level of physiological state of a host-plant” as to efficacy of CESPPs 2.1.1.1.1.3. In other subcategories of Nonpreference - 2.1.1.1.1.1. and 2.1.1.1.1.2. the effect of physiological state of host-plants on their expression still has not been studied.

2.1.1.2. Antibiosis

2.1.1.2.1. Antibiosis to herbivores

2.1.1.2.1.1.1. Antibiosis to herbivores, Structural, Permanent

A number of examples of potent CESPPs 2.1.1.2.1.1.1. and A.2.1.1.2.1.1.1. are provided by grassy plants. First of all, it should pay attention on agricultural crops, in which breeders have produced well-protected varieties, so that within a species there is a wide range of varieties as to their ability to protect themselves.

The variety of the corn Amarga from Argentina having foliage and sheathes covered by dense rigid hairs is resistant to the locusts as well as to drought and heat (Zhukovsky, 1964, p. 201). Further, (Ibid, p. 101) has been reported that wild relatives of the cultivated wheat have serrate spikes protecting seeds of these plants against hoofed animals. This trait is especially developed in Triticum theoudar Reut., so that a temptation to feed by these plants in the period of maturity is dangerous for the animals.

The wild grasses also effectively protect their seeds against such animals. An experience of zoological parks bears the same evidence, namely: "It is very important that hay should not be moldy or musty, and that it does not contain the so-called foxtail and other grasses and grasslike plants (Hordeum, Bromus, and others) that have seeds bearing barbed awns that penetrate the mouth of the animals, causing bad sores which frequently lead to serious ulcers, and occasionally permit infectious organisms to enter through the injures" (Walker, 1942, p. 329).

G.E. Russel (1978. p. 353) has reported that "Several bird-resistant maize varieties have been bred in the USA and some have performed well in field trials (Lenehan, 1977)."

In the sorghum, grain yield is often heavy suffered by the sparrow. Nevertheless, the resistant varieties of this crop are known (Shapel, 1967). These varieties have spikes on seed brooms that threaten bird’s eyes at attacking the seeds. Other sorghum varieties contain high amount of tannin in their seeds that also repel the sparrow. This is, however, another category of Antibiosis.

It has been bred a wheat variety with unusual direction of spikes which make the grain inaccessible for the spike beetle, Anisoplia austriaca Hrbst. (Burdun et al., 1991).

Divers structures of buds, leaves, stems and twigs protect them against the wide range of tiny arthropods. Sticky surface or a dense hair cover preclude moving and feeding by mites and insects particularly in young stages (see for review L.G. Gilbert, 1971, 1972, 1977; L.E. Gilbert and P.H. Raven, 1975, cited in E.R. Pianka, 1978).

In many species, a hair cover is accompanied with a presence of protective substances, which provide the better protection against tiny herbivores and even serve as a means of plant’s nutrition. Such hairs have a duct in their core that leads to a gland under an epidermis. Due to secretion of toxic and adhesive substances through the hairs, little arthropods die on a plant’s surface. Then they are digested by ferments of the secretion, and products of the digestion are absorbed by these plants.

Such traits were observed in some cultivars of the tobacco, Nicotiana spp., the tomato, Licopersicon spp. and the potato, Solanum spp. The pattern of the predation in Solanum spp. was studied by J.J. Neal et al. (1989). These scholars have reported: "Small insects such as aphids may become entrapped on the leaf surface; the mobility of those not entrapped is impaired by accretions of hardened trichome exudes" (p. 134). So, the evolution shifts the situation to diametrically opposite one – a plant consumes its former enemies.

A very dense coating of stellate hairs on a ventral leaf surface in the white limes, particularly Tilia tomentosa and T. petiolaris protects them against the lime aphid Eucallipterus tiliae (Carter and Nichols, 1985). "On these limes most adult aphids are able to feed on the major veins but their new-born nymphs having a shorter rostrum cannot even reach the minor veins where they normally feed. If the trichomes are artificially removed, the young aphids can readily feed and mature. Certain other species, Tilia maximowicziana, T. mongolica and T. euchlora still were unable to support aphids, even after trichome removal. Scanning electron microscope pictures reveal that these species are ornamented with glandular structures located where the aphids feed along the leaf veins" (Ibid., p. 66).

Hence, in the latter three species, CESPPs 2.1.1.2.1.1.1. "Antibiosis to herbivores, Structural, Permanent" is reinforced by 2.1.1.2.1.2.1."Antibiosis to herbivores, Physiological (biochemical), Permanent." Contrary, "The three kinds grown in Britain, T. cordata, T. platyphyllos and, most commonly, T. europea, are all susceptible. These generally have few or simple trichomes to their leaves" (Ibid., p. 66).

As a self-protection against sap-sucking arthropods, it serves hardening of surface tissues at maturation of them. The presence of dense colonies of aphids on juvenile tissues is a common event on stems in grassy and woody plants. Maturation of such tissues leads to appearing of hard cuticule, so that these aphids disappear or move far on a stem (sprout), where tissues are still juvenile.

The effect of hardening of the cuticule on aphids is seen well in the winter wheat. The author observed that in the Kyiv Region (Ukraine) the wheat sown in the middle of September had usually significant density of the greenbug, Schizaphis graminum Rond., when counting in October. In some seasons, the density reached more 1000 aphids per square meter of the soil surface. In the same time, the voluntary winter wheat is free from the aphid. Seeds of this wheat came into the soil in July. In October, such plants had tillers with hard outer tissue, which was unfavorable for feeding of the aphid.

It is known the cases, when structural Antibiosis is used for protection of tree seeds against vertebrate herbivores. The protective structures are formed on stems of such trees. These cases are the honey locust, Gleditschia triacantos L., which has huge thorns in its stems, and the hawthorn, Crataegus macrocarpa L. having a stem of a ramous type with numerous thorns. Such structures constitute an insuperable obstacle for mammals consuming the seeds. These mammals tend to climb into tree crowns ringing out stems with their paws, for example the opossum.

A number of traits of grassy plant species have structures, which can be attributed to CESPPs 2.1.1.2.1.1.1. "Antibiosis to herbivores, Structural, Permanent" operating against hoofed animals. Such traits hamper consumption of them by the animals.

Such plant species as Alchimilla spp., Taraxacum officinale L., Plantago spp. Artemisia austriaca Jacq. and A. frigida Willd. have very short stalks so that their leaves are prostrated on a soil surface. These species become abundant on pastures, which suffer by overgrazing (Larin, 1964 p. 172). In Carlina acaulis L., all the prostrated leaves and a flower in a center of the leaf rosette are provided by sharp thorns. The species of the sedge, Carex spp. have usually slips firm leaves with sharp edges, which easy slip off from animal’s mouth and the leaves are able to cut it. One more means of the self-protection is represented by the mat-grass, Nardus stricta L. This plant is not tall – 10‑40 cm height. Its stalks are thin, slide, are free of knots, leaves are thin and clasped to the stalks, the bunch of stalks is a cone-shaped. The roots are firmly held in the soil. All these traits are aimed to slip off the bunch from an animal’s mouth at grazing.

The good example of usage CESPPs of A.2.1.1.2.1.1.1. "Antibiosis to herbivores, Structural, Permanent" in breeding practice concerned so-called armor-clad varieties of the sunflower resistant against the moth Homoeosoma nebulella Hb.= H. nebulellum Schiff. (the family Phycitidae) as described by V.N. Shchegolev et al. (1949, pp. 530‑532). At the end of XIX century, this tiresome pest laid heavy obstacles to growing of as the sunflower destroying its seeds. The breeders Plachek, Pustovoit and Zhdanov developed the varieties, which produced in seed’s cover between cork tissue and scleronhyma a layer of black color consisting of mainly carbon. When laying their eggs, the moths do not discriminate the susceptible and resistant varieties, but on the latter, the larvae are unable to penetrate into the seeds. The larvae are forced to feed by outer tissues that does not decrease seed yield.

In a result of this prominent achievement, the main oil crop stays free from the damage already during a century.

2.1.1.2. Antibiosis.

2.1.1.2.1. Antibiosis to herbivores

2.1.1.2.1.2.1. Antibiosis to herbivores, Physiological (biochemical), Permanent

2.1.1.2.1.2.2. Antibiosis to herbivores, Physiological (biochemical), Delayed

The spectacular examples of CESPPs 2.1.1.2.1.2.1. "Antibiosis to herbivores, Physiological (biochemical), Permanent" are provided by woody plants. This is so because the traits of such plants (large sizes, expressed differentiation of plant’s parts, a longevity, which reaches a number of centuries), they need in a developed system of tissues of conductive concern – phloem. A damage of such tissues results in dangerous consequences for a tree, and a repair of these tissues is difficult. The self-protection is especially important for a stem of trees. A tree stem might be considered as the only narrow bridge, which connects spacious regions of a tree crown and a root system. In addition, conductive tissues contain a high concentration of nutrients. Therefore, a stem is a dainty dish for numerous species of herbivores. To kill a tree, it is sufficient to obstruct this bridge by a narrow bend of destroyed phloem – a girdling of a stem.

Among stem borer species, the first place is occupied by the bark beetles (Coleoptera: Scolytidae). This is so because the bark beetles are able not only to detect early stage of weakening of host-tree Antibiosis, but also they are able to overcome expressed Antibiosis of healthy trees by means of the mass attack. These species possess by very developed chemical communication, which allows them to aggregate in huge hordes on a surface of selected by them trees. In so doing, myriad of beetles simultaneously cut their way through an outer bark and phloem. The result of this struggle depends on the number of attacking beetles and possibilities of attacked trees to protect themselves.

The most dramatic scenes of a struggle between attacking bark beetles and trees in their antibiotic response one can observe in the coniferous tree species. The self-protection in these plant species is realized by oleoresin exudation. Oleoresin is a toxic and sticky product, which moves in a place, where a surface of a stem is broken, and phloem or sapwood is damaged. Oleoresin is produced by special glands, and it contains in ducts, which in pines and spruces transpierce all the phloem and sapwood of stems, branches and roots. These ducts are united each other composing a common system. This system allows supply wounds by a comparatively very large amount of oleoresin - much greater than a mass of attacking bark beetles on condition that their number is not too much. This kind of self-protection is very effective, but only on condition that a tree under the attack is healthy one, i.e. it is in a proper physiological state. Such trees having optimal water balance due to strong turgidity of tissues exude oleoresin with high pressure.

The values of the oleoresin exudation pressure have been recorded. The highest of them have been observed by Ph. F. Bourdeau and C.S. Schopmeyer (1958) - up to 14 atm. There exists the method of determining of oleoresin pressure by calculation. It gives values of this effect up to 20 atm. (Ivanov, 1961, p. 98).

Oleoresin exudation pressure causes appearing of oleoresin in wounds already few minutes after breakage a phloem surface. At colonization of trees with expressed oleoresin exudation, one may observe active attempts of bark beetles to overcome a protective response of a tree. The beetles push out exuding oleoresin on a stem surface that results in appearing on the surface pitch tubes. The decrease of oleoresin exudation to zero is crucially important for surviving of bark beetle brood.

It was supposed that resistance in coniferous trees to stem borers is determined by toxic effect of oleoresin, whereas at weakening of trees, toxicity of their oleoresin becomes low, and attacking beetles do not encounter obstacles (Smith, 1961; Isaev, 1967, 1971, pp. 33‑34). The data on composition of turpentine depending on physiological state of trees offered above at considering Nonpreference of host-trees to stem borers do not confirm this supposition. Nevertheless, there is a possibility the changing of oleoresin toxicity at various combinations of terpenoids due to hypothetical synergism of them.

To check this hypothesis, it was conducted a study, in which was compared effect on bark beetles turpentine and oleoresin of healthy and weakened trees of the Norway spruce, Picea excelsa (abies) (Vasechko, 1968a, 1970, 1971a). The oleoresin was extracted from phloem of these trees, the turpentine was distilled from samples of oleoresin. Taking of samples of oleoresin on the trees was accompanied determining of oleoresin exudation pressure, rate of oleoresin exudation by the method of P.A. Polozhentzev (1950), and artificial setting of bark beetles on a stem surface of trees under study and subsequent observation of their destiny. Oleoresin exudation pressure was determined with the method close to that developed by J.D. Hodges et al. (1968). The difference was only in details. It was used thick-wall glass capillary tubes sealed on one end. They were inserted in holed punched in spruce bark on depth of outer bark and phloem. According to the Boyle’s law, values of oleoresin exudation pressure were calculated by as ratios of columns of air and oleoresin in the tubes. The toxicity of oleoresin and turpentine was studied by affection on the beetles and larvae in Petri dishes. The obtained data are presented in the Tables 14.

Table 14. The dependence of characteristics concerned turpentine (toxicity) and oleoresin (pressure and exudation) on susceptibility of the Norway spruce, Picea excelsa (abies) for colonization by Ips typographus. Studies in the Carpathians Mountains, Ukraine

Characteristics of sources of protective products

Toxicity of protective product (turpentine),LC-50 mg/cub.cm

Oleoresin exudation pressure

Rate of oleoresin exudati-on

Sources of protective products and effect of the products on Ips typographus

Physiological state of a tree – a source of oleoresin

1

2

3

4

5

Phloem of a tree felled five days before setting of the beetles, the settled beetles colonized the tree

Weakened

0.5007( 0.0379

0

1

Phloem of a standing tree colonized by I. typographus 20-25 days before taking sample of oleoresin

Weakened

0.4898( 0.0486

0

0

Phloem of a standing tree, the settled beetles died in exuded oleoresin

Healthy

0.2714( 0.0043

6

4

Phloem of a standing tree, a the beginning of natural colonization by I. typographus, the settled beetles also successfully colonized the tree

Weakened

0.2538( 0.0042

0

2

1

2

3

4

5

A mass of oleoresin exuded on a stem surface of standing tree, the settled beetles died in exuded oleoresin

Healthy

0.1995( 0.0058

5

4

Table 15. The toxic effect of Norway spruce turpentine on beetles and larvae of bark beetles Ips typographus and Dendroctonus micans. Studies in the Carpathians Mountains, Ukraine

Sources of turpentine

Insects under study

The number (percentage) of died individuals comparing with check at diverse concentrations of turpentine, mg/cub. cm

The level of reliable difference

0.0907

0.1965

0.3477

0.6273

0.05

0.01

1

2

3

4

5

6

7

8

Phloem of a healthy (standing) tree

Beetles of D. micans

—

-8.28

-5.92

-8.07

14.91

19.56

Larvae of D. micans

-2.54

+1.09

+6.18

—

6.99

9.16

Beetles of I. typographus

—

+15.33

+34.92

+56.92

14.14

18.54

Phloem of weakened (felled) tree

Beetles of D. micans

—

-5.07

+4.78

-1.28

14.91

19.56

Larvae of D. micans

-10.50

-4.09

-2.64

—

6.99

9.16

Beetles of I. typographus

—

+21.50

+59.17

+60.17

14.14

18.54

Oleoresin from egg galleries of D. micans

Larvae of D. micans

-5.82

-3.73

-1.36

—

6.99

9.16

Table 16. The dependence of the number of Ips typographus beetles penetrated into phloem of Picea excelsa (abies) on rate of oleoresin exudation and oleoresin exudation pressure at artificial setting of the beetles on tree stems in the number sixty beetles (six replications) per tree

Numeric scores of oleoresin exudation

Oleoresin exudation pressure, atm.

The number of beetles penetrated into phloem on the replications

Mean

Standard (0 on felled tree)

1

2

3

4

5

6

1

2

3

4

5

6

7

8

9

10

0 (on a felled tree)

0

9

7

4

9

9

—

7.6

—

1 (on a felled tree)

0

0

0

0

10

8

7

4.2

- 3.4

1 (on a standing tree)

0

9

6

8

9

—

—

7.2

-0.2

2 (on a standing tree)

0

5

5

0

7

5

—

4.4

-3.2

3 (on a standing tree)

0

0

0

0

0

0

0

0

-7.6

4 (on a standing tree)

3

0

0

0

0

0

0

0

-7.6

* The valid difference with the standard (a felled tree) equals 3.0.

The data of the Tables 14, 15, and 16 allow drawing the following conclusions:

xiv) There are no differences between susceptible for colonization by bark beetles (weakened) host-trees and resistant (healthy) ones as to toxicity of oleoresin and its turpentine. This is so because the difference between trees of these categories in a respect of the toxicity is not valid. The values of the difference are in the range 0.37‑0.76, whereas the table values khi-quadrate index for P=0.05 are much higher – 3.70 and 3.84.

xv) There is no trend of a decrease of toxicity in these products, when trees affected by stressors. Turpentine from a mass of oleoresin on a stem surface has some higher toxicity that that in phloem.

xvi) There exist a difference in susceptibility of bark beetles Dendroctonus micans and Ips typographus to turpentine. This is so because the values of mortality of Ips typographus beetles grow with an increase of concentration of turpentine. This is an evidence of toxicity of the product. On the other hand, an increase of the concentration does not effect on the rate of mortality neither beetles of Dendroctonus micans, nor its larvae. Hence, within the used range of concentrations, host-tree turpentine is not toxic for Dendroctonus micans that suggests more aggressive status of Dendroctonus micans comparing with that of Ips typographus.

xvii) As to Ips typographus, the resistant (healthy) host-trees differ from susceptible (weakened) ones in their capacity to transport oleoresin to spots of beetle’s attacks. As indices of this ability, it serves oleoresin exudation pressure (in resistant trees, it is higher than atmospheric one) and rate of oleoresin exudation (in resistant trees, it has the numeric scores 3 or 4). The trees with such values of indices oleoresin exudation are inaccessible for penetration of attacking beetles into phloem of host-trees at the limited number of attacked beetles (several dozens).

The same values of oleoresin exudation pressure and rate of oleoresin exudation determine the resistance of Picea excelsa (abies) and P. orientalis Link. for Dendroctonus micans (Vasechko, 1968).

The similar results were obtained at studies of oleoresin characteristics of the Pinus taeda in the context with its resistance to Dendroctonus frontalis (Strom et al., 2002, p. 169), namely: "Multivariate analysis of variance showed that the concentration of 11 oleoresin chemical components did not differ between trees from escape and general populations (P > 0.619), providing evidence against importance of this potential resistance factor... Oleoresin flow, on the other hand, was significantly higher in escape trees - averaging 1.65 times higher that general population trees over the course of 28 months (eight sampling times). This strongly supports the hypothesis that oleoresin flow can impact the host selection process of Dendroctonus frontalis and suggest that increased flow can improve survival under heavy pressure from Dendroctonus frontalis."

The facts of successful colonization by bark beetles of host-trees with high oleoresin exudation do not contradict the conclusion that this physiological phenomenon is indeed CESPPs and that Nonpreference of host-trees operates only in trees having this state. The matter of facts, when a resource of weakened host-trees is less than a food demand of a bark beetle population, aggressive species of these insects are able to colonize by means of the mass attack actually healthy trees in spite of operation in them CESPPs 2.1.1.1.1.3. "Nonpreference to herbivores, Of unknown nature" and potent 2.1.1.2.1.2.1 "Antibiosis to herbivores, Physiological (biochemical), Permanent." Nevertheless, such a success in the end leads to a decrease of density in this population due to overcrowding of the brood.

In the firs (Abies spp.), the system of oleoresin ducts is absent, but in their phloem, there are numerous little containers with oleoresin (blisters), which excrete oleoresin under pressure, when attacking insects tray to gnaw the phloem.

CESPPs 2.1.1.2.1.2.1. "Antibiosis to herbivores, Physiological (biochemical), Permanent" in stems of the deciduous tree species has been observed by many scholars. In the stony fruit trees (prunes, apricots, cherries, and peaches) and the citrous species, the self-protection is realized by gums – viscid products, analogous to oleoresin in the coniferous species. In the ashes (Fraxinus spp.), the stem borers attacking their stems meet with sap, which dries out quickly on a stem surface turning into mannitol. In mannitol masses, one may find killed beetles or larvae. The poplars protect themselves with a copious sap exudation. The prerequisite of effective self-protection in the deciduous tree species against stem borers is the normal water regime of a tree.

It is important that even very strong inhibitors of insect feeding do not protect trees against stem borers, if these trees are weakened. For example, the birch, Betula verrucosa Ehrh. has very high content protective substances in its bark. It is possible to obtain up to 29 kg of tar from 100 kg of birch bark. Nevertheless, being weakened, birch trees are colonized by numerous species of stem borers.

Strong inhibitors are present in the yew, Taxus baccata L., and in the maiden hair tree, Ginkgo biloba L. Such substances provide the nearly complete immunity all the parts of a tree in these species as to herbivores, when the trees are healthy, but being weakened, they can be attacked by pest insects, in particular by the ambrosia beetle, Xyleborus (Anisandrus) aequalis Reitt. (Stark, 1952, p. 429). Roots the yew tree are colonized by the bark beetle, Hylesinus ater (p.sosna) Payk. (Karpinsky and Strawinsky, 1948, p. 62).

The events at interaction between coniferous trees and bark beetles have been studied well. The review of such data one may find in publications by J. Rudinsky (1962), R.W. Stark (1965) and G.I. Vasechko (1981).

The protective role of oleoresin exudation has been proved also as to other groups of stem borers, namely: the buprestid beetle, Melanophilus californica Van Dyne on Pinus ponderosa by A.S. West (1947, cited in N.P. Naumov, 1963, p. 75‑76), the longhorned beetles (Cerambyx spp.) on the Scots pine (Polozhentsev, 1953), the longhorned beetle, Xylotrechus altaicus Gebl. on the Siberian larch (Rozhkov, 1981).

In conductive tissues in tree’s crown of the coniferous species, oleoresin exudation as a response to damage can be observed from large boughs to twigs of a current season. As to the twigs, the operation of oleoresin exudation is demonstrated by pine bark beetles of the genus Blastophagus (Tomicus). These beetles use pine twigs for imaginal feeding and hibernation. After ceasing of oviposition, these beetles penetrate into a core of twigs on growing pine trees and feed in them. This results in breakdown and fall down of these twigs. In them on a surface of the soil, the beetles hibernate. On an end of these twigs, it presents often a droplet of oleoresin, which has been pushed out of a canal run through by a beetle. These beetles are relatively large in their genus and rather tolerant to oleoresin. Nevertheless, they make a choice among trees, when attacking their shoots for the feeding. They aggregate on trees within forest edges, where trees are weakened by a surplus of sun insolation, and in the stands affected by forest fires. These stressors (excessive insolation or forest fire) reduce oleoresin exudation.

As to minute species of bark beetles, which attack twigs of coniferous trees for oviposition, the complete ceasation of oleoresin exudation is necessary for surviving of their brood.

The bark beetles provide us by the examples of CESPPs 2.1.1.2.1.2.2. "Antibiosis to herbivores, Physiological (biochemical), Delayed." The rate of oleoresin exudation in coniferous trees is very changeable being depending on weather situation. At drought, when the rate is low, bark beetles are able to penetrate into phloem of their host-trees. An onset of wet weather leads to increase of the rate, and affected trees are able to kill or expel penetrated beetles by means of exudation of oleoresin into their galleries. Further, the space around these galleries becomes soaked with oleoresin. This proceeds in a result of conversion of cells in phloem parenchyma neighboring the galleries into the glands, which produce oleoresin. This leads to destruction of fungi inoculated by bark beetles and their brood.

This phenomenon, which is called "resinosis" has been recorded in the spruce (Picea sp.) by F. Schwerdtfeger, 1950, cited in J. Rudinsky et al. (1971), in the pine (Pinus sp.) by R.W. Reid et al. (1967) and the fir (Abies sp.) by A.A. Berryman and M. Ashraf (1970).

Parental bark beetles of Dendroctonus ponderosae counteract the protective response digging long (up to one meter) egg galleries directed upwards to stem portions with less humidity, or winding egg galleries, that is characteristic particularly for Dendroctonus brevicomis. Such galleries enhance drying of phloem that suppresses the 2.1.1.2.1.2.2. "Antibiosis to herbivores, Physiological (biochemical), Delayed." Then, the oviposition begins.

There is a view that destroying of bark beetles and their brood in phloem is a normal response of host-trees on attacks of these pests. Such a conclusion might be drawn from the report by E. Christiansen (1988), where the discourse is limited by the effect of oleoresin in galleries and resinosis. In reality, the protective response in phloem is characteristic for weakened trees. If the onset of wet weather is delayed or density of attacked beetles is High, even heavy showers do not protect attacked trees from perish. Healthy trees kill or repel attacking bark beetles soon after they begin to bore into phloem responding by means of CESPPs 2.1.1.2.1.2.1. "Antibiosis to herbivores, Physiological (biochemical), Permanent."

In shoots of young pine trees, Antibiosis (2.1.1.2.1.2.1.) has been studied well. Buds of the shoots are often attacked by several species of the pine shoot moth, Rhyacionia (Evetria, Petrova) spp., which deface the trees and decrease their worth. P. Harris (1960) offered a review of literature and own data, which showed clearly that survivorship to adulthood of Rhyacionia buoliana Schiff. was determined by rate of oleoresin exudation on attacked host-trees. C.C. Brooks and J.M.B. Brown (1936) paid attention on protective behavior of the young larvae, which evaded from very resinous buds, and lined a silk web, which prevented oleoresin flow from oozing into the mine. A.D. Voute and J.F.G.M. Walenkamp (1946) reported that the larvae developed successfully in mines done in buds on cut shoots, but disappeared from buds on living Scots pines. It is important their observation that hot and dry weather decreases turgor pressure in pine tissues, which in turn decreases rate of oleoresin exudation; just in the period of such weather situation, Rhyacionia buoliana is successful in colonization of host-trees.

Experiments and observations by P. Harris (1960) added new data. It occurred to be the larvae can remove droplets of oleoresin oozing from their mines in the buds, if these droplets are small. Manipulating by their moth parts, the larvae make small beads of oleoresin and spread them on the silk tent outside of the bud. Also, to prevent of sticking, the larvae treat droplets of oleoresin with their saliva that promotes the crystallization of oleoresin.

The survivorship on diverse species of the pine was different, and it depended on either their potency to exude oleoresin or its properties. The properties concerned a capacity of the larvae to neutralize oleoresin. The Corsican pine, Pinus nigra Arn. having larger resin ducts and the greater exudation than Pinus silvestris is more resistant than the latter, so that a potency of great exudation corresponds resistance of pine species to the pine shoot moths.

The lodgepole pine, Pinus contorta Dougl. has rate of oleoresin the same as Pinus nigra, but the survivorship on the former is higher that is explained by capacity of its oleoresin to loss stickiness easily under effect of the saliva.

Duration of the development of the larvae decreased at drought, when exudation was minimal. Outbreaks of pine shoot moths arise in areas, where drought is common

In Russia, the view as to the crucial role of oleoresin exudation in host-plant resistance to the pine shoot moths has been shored by L.T. Krushev (1957, 1973, p. 10).

It is almost impossible to find the pine shoot moths on the Crimean pine, Pinus pallasiana Lamb. in any plantation established in south Ukraine, the Low-Dnieper area. Contrary, Pinus silvestris in this area are damaged heavily by these species, when growing in pure composition or jointly with Pinus pallasiana. The latter species should be considered as a host-tree for the moths, because they lay their eggs on buds of this species, but young larvae are unable to penetrate into thick cover of its buds or die under effect of abundant oleoresin flow. This fact was stated by M.M. Padiy (1969). This is a remarkable fact – Pinus pallasiana is attractive for oviposition likely other host-plants, but it has the developed CESPPs 2.1.1.2.1. "Antibiosis to herbivores" and, therefore, is resistant. It might be independetly to further survivorship of a brood, oviposition is a criterion for demarcation of a host-tree from a nonhost-tree species.

Z.S. Golovyanko (1909, 1949) was probably the first scholar, who studied a self-protection of pines against grubs of the cockchafer, Melolontha spp. He found out that in the conditions of abundant supplying by moisture, roots of pines pushed out of attacking grubs by copious exudation. Some young larvae in a result of such response occurred to be dead. On the other hand, at water deficiency in