THE ENTOMOPHAGOUS FAUNA AND ITS ROLE IN PRESERVING … · THE ENTOMOPHAGOUS. FAUNA AND ITS ROLE IN...

Analele Științifice ale Universității „Al. I. Cuza” Iași, s. Biologie animală, Tom LVI, 2010

THE ENTOMOPHAGOUS FAUNA AND ITS ROLE IN

PRESERVING THE NATURAL BALANCE

Gheorghe MUSTAȚĂ and Mariana MUSTAȚĂ

“Al. I. Cuza” University Iași, Faculty of Biology, Bd. Carol I 20A, 700505 Iași, Romania, [email protected]

Abstract. Based on research effectuated for four decades on the role of entomophagous insects in the limiting of

populations of some insects harmful to crops of cabbage in Romania, we have identified the complexes of

parasitoid insects controlling the populations of some harmful Lepidopterans belonging to the species:

Helicoverpa armigera Hubner, Autographa gamma L., Mamestra brassicae L., Pieris brassicae L., P. rapae L.,

P. napi L. and Plutella xylostella L.We elucidated the trophic relationships characteristic to these biocoenotic

complexes and made the trophic networks self-evident in this respect. We develop the concept of parasitoid

biocoenoses and demonstrate their role in maintaining the balance of nature; we present the effect provoked by

the anthropic impact on the functioning and efficiency of parasitoid biocoenoses as a result of imbalances caused

by human being in the control activity of some harmful insects.

Keywords: pests, parasitoids, hyperparasitoids, predators, entomophages, entomophagous biocoenoses,

parasitoid biocoenoses , biological control, natural balance.

Rezumat. Fauna entomofagă și rolul ei în păstrarea echilibrului natural. Pe baza cercetărilor efectuate timp

de patru decenii privind rolul insectelor entomofage în limitarea populațiilor unor insecte dăunătoare culturilor

de varză din România am identificat complexele de insecte parazitoide care controlează populațiile unor

lepidoptere dăunătoare aparținând speciilor: Helicoverpa armigera Hubner, Autographa gamma L., Mamestra

brassicae L., Pieris brassicae L., P. rapae L., P. napi L. și Plutella xylostella L. Am elucidat relațiile trofice

caracteristice acestor complexe biocenotice și am întocmit rețele trofice edificatoare în acest sens. Dezvoltăm

conceptul de biocenoze parazitoide și demonstrăm rolul acestora în menținerea echilibrului natural; prezentăm

efectul provocat de impactul antropic asupra funcționării și eficienței biocenozelor parazitoide în urma

dezechilibrelor provocate de om în activitatea de combatere a unor insecte dăunătoare.

Cuvinte cheie: dăunători, parazitoizi, hiperparazitoizi, prădători, entomofagi, biocenoze entomofage, biocenoze

parazitoide, control biologic, echilibru natural.

Introduction

Following the evolution of the world we find that insects had a parallel evolution

with the higher plants with flowers. There is no species of flowering plants that do not

become the target of the attack of some phytophagous insects. They attract, by their

presence on the host plants, a series of entomophagous insects (predatory and parasitoids)

that control their populations. As regards the species of parasitoid insects, these can act as

primary, secondary, tertiary and quaternary parasitoids.

In a biocoenotic system of parasitoid type, relationships of cybernetic type are

established ensuring the formation of some self-adjustment mechanisms which do not

allow the exponential development of some species in conformity with the model in Fig.

1.

We have to understand that these complexes of parasitoids that control the

populations of some species injurious to plants do not represent a sum of species

associated by chance, on the contrary they form biocoenotic complexes of particular type -

parasitoid biocoenoses, in which the species in their existence depend on each other and

on the functional whole they make it together. We bring evidence by which we

demonstrate the role of these biocoenoses in the keeping of natural balance, as long as

some anthropic perturbation factors do not act to cause a certain imbalance between

species affecting the integrality of the biocoenotic complex.

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Gheorghe Mustață & Mariana Mustață

Figure 1. The cybernetic mechanism of self-adjustment, characteristic to some biocoenoses of

parasitoid type.

The structure of some parasitoid biocoenoses and their role in preserving the natural

balance

Jourdheuil (1960) developed the concept of parasitic biocoenosis on the basis of research

effectuated on some parasitoid hymenoptera controlling the populations of some

coleopterans harmful to cruciferous plants.

But we consider that the most appropriate term for such biocoenotic complexes is

that of parasitoid biocoenoses because it is the matter of parasitoids and not of parasites.

The parasitoid biocoenosis is the most suitable frame in which it has to be studied the

endless interrelationships that are established between plants and the phytophagous insects

that attack them and between the phytophagous insects and the parasitoid species that

control their existence. To better understand the concept of parasitoid biocoenosis, we

shall put into discussion the parasitoid complexes controlling the populations of some

insects harmful to crops of cabbage in Romania.

Helicoverpa armigera Hubner, known also under the popular name as the

caterpillar of cotton capsules normally attack the cotton capsules and the maize (the corn

cob). Because the cotton crops in Romania disappeared, and the species has passed on

other plants too, it also attacks the cabbage crops in the south of Romania.

Probably, in cotton crops the species has been maintained below the economic

threshold of damage by chemical treatments so that this pest has not realized an

exponential development. In cabbage crops, the populations of this pest are controlled by

fewer species, and the degree of parasitation is low enough, between 5-10%. We have

identified the species: Trichogramma evanescens Westw., Macrocentrus collaris (Spin.),

Rogas rossicus Kok. and Microplitis rufiventris Kok.

Patriche (2003) mentioned the presence of the species Hyposoter didimator

Thunbg. in the populations of H. armigera.

In the research in Romania there were still cited other species too of primary

parasitoids that have limited the populations of this species in the cotton and maize crops,

namely: Chelonus oculata Panz., Rogas dimidiatus Spin., Barylypa humeralis Brauns,

Rogas testaceus F., etc. (Perju et al., 1988, 1989).

The species Trichogramma evanescens Westw. presents a higher efficiency in

limiting the populations of this pest that parasites sometimes the eggs in proportion of 15-

20%.

As we stated, H. armigera entered in the cabbage crops in the recent decades. It

does not provoke damages in the cabbage crops. The species behaves as if it would has

been introduced recently in Romania. The impression is false and it is determined by the

fact that in the crops of cabbage it was not followed by the complex of parasitoids that

control it in the cotton crops. We can not speak of a complex of parasitoid species to

really limit its populations.

Producer Phytophagous

consumer

Parasitoid II Parasitoid I Parasitoid III

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Figure 2. The trophic network specific for the populations of Autographa gamma L.

H. armigera deserves to be followed in its evolution in order to be surprised the

way in which the complex of parasitoids is reorganized controlling its existence.

Autographa gamma L. is a species of noctuids with a broad spectrum of

polyphagy, which attacks many species of spontaneous and cultivated plants. We have

identified a fairly large number of species of primary parasitoids and in recent decades

also the intervention of some species of secondary parasitoids, but the efficiency of

parasitoids in limiting the populations of A. gamma was low enough (Mustață, 1973;

Mustață et al., 2000).

In Fig. 2 we present the trophic network specific to this biocoenotic complex.

Except those 17 species of primary parasitoids, other three species of secondary

parasitoids appear too; the action of the latter is practically negligible. However, as we

will find in the species Mamestra brassicae L. too, this biocoenotic complex begins to

take shape and become functional, the trophic network could result in reorganization and

it leads to the consolidation of the complex in the next stages.

We should mention the fact that the populations of A. gamma are reduced by the

parasitoid complexes in proportion of 15-20 %. Trichogramma evanescens presents an

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increased efficiency which can achieve percentages of parasitism of eggs of 40-50 %

(Mustață, 1973; Mustață et al., 2000).

Very interesting is the species Copidosoma truncatellum (Dalm.) presenting the

phenomenon of polyembryony. From a single larva of A. gamma parasited by this species,

we have obtained up to 2,500 individuals. In such a prolificacy we would have expected,

that over the generations the presence of this parasitoid in the populations of A. gamma,

be increasingly higher. We did not find that, and we did not find the mechanism that does

not permit the numerical increase of the species C. truncatellum.

Mamestra brassicae L. can be considered the most dangerous pest of cabbage

crops in Romania. Young larvae are gregarious and eat the cabbage leaves. In this period,

many of them can be parasitized by different species. Mature larvae spread on the host

plant and can pass on other plants too, then they get into the interior of the bulb making

large galleries in which faces are stored, what it determines the total compromise of

plants. A number of 3-4 mature larvae can compromise a cabbage bulb of the size of a

child head. The pupation takes place in the ground so that the pupae are somewhat

protected against parasitoids. But there are species which parasite the pupae too.

Figure 3. Trophic network specific to populations of Mamestra brassicae L.

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In our research we obtained a rather large complex of parasitoid species (Fig. 3),

but the parasitation percentage of larvae and pupae was always reduced, between 10-15%,

rarely 20 %.

Besides those 18 species of primary parasitoids, other 7 species of secondary

parasitoids act too. It is interesting the fact that the parasitoid species do not put in danger

the populations of M. brassicae to such an extent to be necessary the intervention of

secondary parasitoids. However, by the presence of the primary parasitoids in the larvae

of M. brassicae some species of secondary parasitoids are attracted too, with a broader

spectrum of polyphagy. If we make a synecological analysis of this complex of

parasitoids, we shall find that the secondary parasitoids act as accidental and subrecedent

species in the complex (Mustață et al., 2000).

The trophic network is quite complex, but it appears to be “coupled” perfectly

functional to be able to limit the multiplication of the species M. brassicae.

We obtained a higher efficiency from the species Trichogramma evanescens in

what regards the parasitation of eggs. But we must mention that in the period 1967-1971

we obtained very low percentages of parasitation of eggs, around 10-15 % (Mustață,

1973), but in the period 1972-1974, and even in recent decades we have obtained from

several cabbage crops attacked by M. brassicae, percentages of parasitation of eggs

comprised between 50-60 % (Mustață et al., 2000). The explanation can be given by the

fact that the species T. evanescens, being a species with a wide spectrum of polyphagy,

can easily pass from one host to another one, making part of the so-called buffer system of

some larger biocoenotic complexes, such as an agrobiocoenosis – the cabbage crop.

It is interesting the situation met in the case of the species of Pieris. We observed

the presence of the species: Pieris brassicae L., P. rapae L., P. napi in the cabbage crops.

These related pest present an impressive number of parasitoids controlling their

populations.

Pieris brassicae is the most harmful species to cabbage crops, but by the way in

which the larvae eat the leaves, in their gregarious phase, provoke the immediate reaction

of the producers who ravage the crops with chemical substances. In the crops where there

was not used chemical substances, we obtained an impressive number of parasitoids, but

rather high degrees of parasitation, 60-70 % and in some crops 80-85 %, which means that

this species is strongly controlled by the complex of parasitoids (Mustață & Andriescu,

1972-1973; Mustață & Costea, 2000; Mustață et al., 2000).

The attack of the species Pieris rapae seems somewhat masked because the eggs

are laid isolated and the larvae also feed isolated, which does not cause a prompt reaction

from the part of producers.

The parasitoid species are common for this species, but their attack depend on

the biomass offered. The biggest biomass can be offered by P. brassicae because the eggs

are laid grouped, and the larvae are gregarious in the first stages.

In Fig. 4 we present the trophic network specific for the populations of Pieris.

Those 23 species of primary parasitoids have a very high efficiency in limiting the

populations of these pests. But what is alarming for the experts in agriculture is the fact

that those 23 species of primary parasitoids are controlled by 16 species of secondary

parasitoids. They have increased in number over the last decades and increased also

significantly their capacity to limit the populations of some primary parasitoids.

If primary parasitoids, by their joint action have succeed to maintain, in most

cabbage crops, these pests below the economical damaging threshold (Mustață, 1973;

Mustață & Costea, 2000; Mustață et al., 2000), their efficiency is much reduced by the

intervention of secondary parasitoids.

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Figure 4. Trophic network specific to populations of Pieris.

The species: Cotesia glomerata, Hyposoter ebeninus and Cotesia rubecula,

which act as euconstant, eudominant species and with the raised ecological index of

significance, are limited in proportion of 35-45 % and in some crops of 60-65 %, what is

something right alarming. Following in time the evolution of this biocoenotic complex we

found that its structure had a complex dynamics.

Professor Mihai Constantineanu has shown since 1929 the contribution of the

species Cotesia glomerata, Hyposoter ebeninus, Pimpla instigator, Aplechthis

compunctor etc. in limiting the populations of Pieris brassicae (Constantineanu et al.,

1957). In our research we found that some species of parasitoids that in the first half of the

twentieth century had a major contribution to reducing the populations of P. brassicae,

now no longer appear, or appear as accessory and incidental species such as the species:

Brachymeria femorata, Hemiteles melanarus, Pimpla instigator, Theronia atalantae etc.

What is more important is the fact that this biocoenotic complex, so much modified, as we

perceive it in this period, controls the populations of Pieris with the same efficiency. The

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reorganization of the trophic network specific to this biomass of parasitoid type appears as

a necessity imposed by the use of chemical weapon of control and the serious imbalances

provoked by the anthropeic impact. It seems to us alarming the increase in recent decades

both the number of secondary parasitoids and the high efficiency of some species in

limiting of some primary parasitoids.

We will show a similar situation in the biocoenotic complex of the species

Plutella xylostella L. and we will try to find some reasonable explanations.

We are not wrong if we say that nature is intelligently structured, and that the

biological adaptation means, in the present case, some reorganization of the whole (of the

trophic network of the complex) so as to meet the new requirements imposed by

environment and especially by the human impact. As regards Plutella xylostella, this is a

cosmopolitan species that is found all over the world meridians where the cabbage is

grown. It is interesting that some populations are capable of migration and can cross large

distances.

In Romania, it presents usually 3 generations in the south and 2 in the north, in

certain years it may have 4 or 5 generations in the south and 3-4 in the north, depending

on temperature. In tropical regions it can reach up to 20 generations per year.

In Romania, P. xylostella is controlled by an impressive complex of parasitoid

species. In the conditions of Moldavia, we were able to identify over 50 parasitoid species

limiting the populations of this pest.

Not only the number of parasitoid species in this biocoenotic complex impresses,

but also the fact that the populations of Plutella xylostella are strongly limited, being kept

below the economic damaging threshold. The degree of parasitation of this pest exceeds,

usually, 50 % and in some crops it may reach up to 90-95 % (Mustață, 1973, 1992;

Mustață & Mustață, 2001). In this situation it is natural to ask ourselves why this species

is still maintained as a pest of cabbage crops. We could find some explanations:

Intervention with chemical substances to control of P. xylostella even in the populations in

which the parasitation degree reaches to 80-90 % (Mustață, 1973, 1992; Mustață &

Mustață, 2001), which represents real ecological crimes. Another explanation would be

that P. xylostella is capable of migration and it passes easily from one culture to another

one and from one area to another.

In Fig. 5 we present the trophic network specific for populations of P. xylostella

and the complex of parasitoids: of those 42 parasitoid species, 24 act as primary

parasitoids and 18 species as secondary parasitoids.

In the conditions of the years 1970-1973 we identified in the populations of P.

xylostella in Moldavia a number of 32 species of primary parasitoids and 4 species of

secondary parasitoids. (Mustață, 1973). In the research effectuated in the period 1967-

1972, we collected from 37 localities in Moldavia 8,246 mature larvae and pupae

(chrysalis) of P. xylostella. 7,239 adults hatched belonging to the pest and to the complex

of parasitoids. A number of 1,212 individuals belonged to the host (P. xylostella) what

represents 14.7 %, the others belonging to no more than 27 species of primary parasitoids.

The degree of parasitation of P. xylostella ranged between 29.40%, the lowest at Valea

Lupului, Iasi, on August 27th and 100% at Vlăsinești, Botosani, on August 4th, 1970

(Mustață, 1979).

The data were published, the paper was found and consulted by some specialists

from Taiwan, from the AVRDC, who were impressed both by the large number of

parasitoids and the degree of parasitation of this pest.

Being invited to a Congress in Tainan, Taiwan, in 1990, the specialists from

there told me that in their cabbage crops only one parasitoid is present, Cotesia plutellae

and it limits the populations of P. xylostella with less than 1%.

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Figure 5. Trophic network specific to populations of Plutella xylostella L.

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At the Congress in Taiwan we presented a trophic network with a number of 26

species of primary parasitoids and four species of secondary parasitoids on the basis of the

research effectuated in Moldavia in the respective period (Mustață, 1992).

In 2001and 2006 we were pointing out the alarming growth of the secondary

parasitoids species and their efficiency in limiting of some primary parasitoids. We were

launching an alarm signal on the fact that some species of primary parasitoids were

strongly limited by secondary parasitoids (Diadegma armillata in proportion of 40.2%

and D. fenestralis 29.8 %) (Mustață et al., 2006).

Returning to Fig. 5, we cannot but remain impressed by the very big number of

secondary parasitoids acting within this biocoenotic complex.

We consider that this complex formed of: the host plant – P. xylostella – primary

parasitoids – secondary parasitoids forms a biocoenosis of parasitoid type, like other

parasitoid complexes of other presented species, functioning as a organization level well

structured and that has a certain dynamics in the reorganization of the trophic network in

time and space.

It is known that maintaining the optimal number of individuals within a species

(population) can be achieved through well defined cybernetic mechanisms of self-

adjustment. The number of individuals in a population expresses the state of prosperity or

its decline.

In the conditions of Romania (in Moldavia, particularly) the species P. xylostella

is strongly limited by the complex of parasitoids and the species of Pieris. In Taiwan and

Southeast Asia where P. xylostella has about 20 generations per year, multiplying itself

similar to aphids, the species becomes an extremely dangerous pest. In this part of the

world the species behaves similar to the species Leptinotarsa decemlineata in Europe,

because it arrived, through migration, or by other routes in this zone without being

accompanied by the entomophagous complex which could limit its populations.

Moreover, starting from the very big complex of parasitoids that control the

populations of Pieris and P. xylostella, we have reached to the conclusion that these

species have their world genetic center (according to N. Vavilov's conception) in this part

of Europe.

What is actually happening?

The complex of species that controls the populations of P. xylostella behaves as a

unitary whole, as a biocoenotic complex, as we were presenting early. By its presence in

the cabbage crops P. xylostella provides an important biomass of larvae and pupae (less of

eggs, which are somewhat hidden in the host plant tissues) for the species of primary

parasitoids. In their dynamics to occupy a certain number of female hosts, the parasitoid

species are found in a close competition. The host being quite small, usually in a host

develops one parasitoid. There are few exceptions when in a host several individuals

develop, as in the case of the species Trichomalopsis and Oomyzus sokolovskii.

In this competition a species or another wins depending on certain factors.

Making a synecological analysis of the parasitoid species acting in certain populations of

P. xylostella, we can find that some species act as eudominant, euconstant species, with a

high ecological significance index, while other species appear as being accessory and

accidental and with a very low ecological significance index. This means that the species

have different contributions in limiting of host populations .The situation can change from

one crop of cabbage to another, from one year to another or from one area to another. The

biocoenotic complex functions normally even if the trophic network structure has other

configurations in time and space. In such complexes we can feel how perfectly the

ecological principle functions – everything depends on everything.

P. xylostella, offering a big biomass by its individuals, attacks the species of

primary parasitoids. These succeed to limit considerably the populations of this pest in the

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conditions of our country putting in real danger its existence. One can say that in certain

cultures of cabbage or smaller lots, P. xylostella may be parasited to 90 % or even 100%,

what constitutes a threat to this species and it could reach to its extinction. But, normally,

this does not happen, because the primary parasitoids, limiting the populations of P.

xylostella, attract by their presence a series of species of secondary parasitoids, which

limits their actions. The number of the species of secondary parasitoids grows in time

depending on the biomass of larvae of primary parasitoids that are offered to them. Thus,

we feel how within this complex comes into operation a cybernetic mechanism assuring

the numerical control of the populations within the biocoenotic complex. It is actually just

the situation we pointed out, being alarmed by the increase of the number of secondary

parasitoids acting in this complex and by the increase of their efficiency.

Our alarming signal has appeared naturally, as we were looking the entire

biocoenotic complex by the angle of human economy, not of nature economy. We were

excited by the big number of primary parasitoids which conjugate their actions in limiting

the populations of P. xylostella in certain cultures, without agriculture to use biological

method to control this pest. No parasitoid insects were reared to be launched in nature to

combat Plutella. If the actions of the primary parasitoids are beneficial to human

economy, the interventions of secondary parasitoids are totally useless or even

compromising. Even in the situation in which we launch in the cabbage crops certain

species of primary parasitoids to combat P. xylostella, their efficiency would be greatly

limited after a few generations.

But, if we look at these relationships by the angle of interests of nature economy,

we discover those mechanisms that can allow the perfect functioning of complex.

Let’s resume the logical thread of the deployment of trophic relationships among

the species of this complex and the reorganization of the trophic network. P. xylostella

acting in the populations of Brassica oleracea can undermine some cultures, especially in

the case of young plants, destroying their buds. In such situations the producer is in

danger. Often it happens that some cultures are compromised by some pests. In Taiwan,

this happens quite often if one does not intervene quickly for control.

Even if some cultures are compromised in certain zones, the situation could be

another in other areas. The saving of the producer could come from the species of primary

parasitoids that enter into operation and act in the populations of P. xylostella. The species

of primary parasitoids conjugate their actions and realize the limitation of the species P.

xylostella below the threshold of economic damage. Thus, a new critical situation appears

within this biocoenotic complex. Brassica oleracea var. capitata was saved, but it is

exposed to risk of extinction the species P. xylostella, which has its role within this

complex, as the existence of this depends on many parasitoid species. For saving the

species P. xylostella from extinction, the secondary parasitoids enter into action. While

the number of species of secondary parasitoids increased, their efficiency also increased.

This seems to be the situation in the cabbage crops in Romania attacked by P. xylostella

and Pieris in the present stage.

To ensure a permanent control of the relationships between species it would be

necessary the existence of buffer system that not to allow the exponential growth of a

species. Analyzing the trophic network of this biocoenotic complex, we discover the

species Oomyzus sokolovskii. This species act both as primary parasitoid and as secondary

parasitoid, what demonstrates that this biocoenosis of parasitoid type is approaching to the

climax state.

O. sokolovskii acts as primary or secondary parasitoid depending on the biomass

of host larvae offered. Thus this species was identified as primary parasitoid of P.

xylostella and as secondary parasitoid of the species Apanteles plutellae and Cotesia

plutellae, species that manifest as being euconstant and eudominant and providing a big

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numbers of larvae that can be parasitized. Having at their disposal the larvae of these

primary parasitoids, the females of O. sokolovskii prefer them more as hosts for their

larvae. And so they limit much their number.

Nature’s economy works in such a way so that within the biocoenotic complexes

do not appear imbalances provoked by the exponential growth of some species.

In the moment when in a biocoenotic complex of parasitoid type appears a

serious imbalance among species, it can no longer function normally the cybernetic

mechanism that ensures the evidence of the exponential growth of a species and the

keeping of natural balance. The biocoenotic complex can make in a somewhat extent its

trophic network, but it is not any more perfectly coupled to the mechanism of self-

adjustment and thus some species may have an exponential development. It’s about what

it happens in the populations of M. brassicae and Autographa gamma, where the trophic

network is fairly well defined, but it does not ensure any more the re-establishment of the

balance among the species of the complex. Accepting these truths, we realize that we must

radically change our behavior when trying to achieve the control of a species injurious to

culture plants. We do not work with an isolated species, but with a biocoenotic complex.

The so-called pest control specialists do not see but the pests and the culture plants. For

them there is no predatory species nor parasitoid ones, and they act simplifying the things,

but with serious consequences. Any intervention on chemical or biological path cannot be

done without a competent synecological analysis to identify what are the species in the

respective biocoenotic complex, what are the trophic relationships among the species and

the numerical relationships among them. A control action made without such a

synecological analysis is a blind action and it can turn into a real ecological crime (as we

often met).

We must understand and accept the existence of biocoenoses of parasitoid or

entomophagous type and to change our concept of control of some harmful insects. No

species can live alone. Interpreting biosemiotic the species and the biocoenosis, we can

affirm that the species is a swarm of swarms, which is part of a larger swarm and which is

the biocoenosis (Mustață & Mustață, 2008).We should not believe that we must grow

parasitoid biocoenoses in laboratories to launch them in nature, but we cannot afford to

intervene in such complex biocoenoses without knowing them perfectly from structural

and functional point of view.

This concept opens our eyes to see and understand that we can not intervene in

the control of a species without taking into account the whole of which it belongs

(parasitoid or entomophagous biocoenosis).

Conclusions

In the present paper we proposed ourselves to present the parasitoid complexes

that limit the populations of some species injurious to cabbage crops, that is about the

entomophagous fauna (predatory or parasitoid) and about its role in the keeping of natural

balance.

We have analysed the parasitoid complexes that control the populations of some

species of lepidopterans that attack the cabbage crops in Romania: Pieris brassicae L., P.

rapae L., P. napi L., Plutella xylostella L., Mamestra brassicae L., Autographa gamma L.

and Helicoverpa armigera Hubner. On the basis of the research carried out over four

decades we have accumulated enough data by which to demonstrate that these parasitoid

complexes form true biocoenoses, namely biocoenoses of parasitoid type (or

entomophagous biocoenoses), which have an important role in the keeping of natural

balance.

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As a result of human impact, of the intensive development of agriculture and use

of chemical weapons in the control of harmful insects, serious imbalances have been

produced in nature, and some parasitoid biocoenoses were affected in their function.

On the basis of the experience accumulated and concrete examples provided, we

draw the attention of experts that they do not have the right to intervene to control a pest

without a thorough analysis of the species that act in the respective ecosystem, without

knowing which is the structural-functional state of entomophagous biocoenoses. This

analysis is obligatory, indifferently whether the chemical weapon or biological control are

used.

In this sense we draw the attention that in the control of pests it should move to a

new concept, that of using the entomophagous biocoenoses (parasitoids) not to cause new

imbalances in nature.

Species do not live in isolation. When we intervene in the control of harmful

insects, we do not work only with the respective species and the attacked plant, but we

work with an inextricably biocoenotic complex.

The concept of using the parasitoid or entomophagous biocoenoses to control the

pests and to maintain the natural balance does not mean the rearing in laboratories of such

biocopenotic complexes and their launch in nature (because it is not possible), but truly

scientific knowledge of the biocoenoses in which we intervene, through a competent

synecological analysis to know exactly the structural-functional status of the respective

biocoenotic complex.

In nature no species can live isolated, functioning perfectly the ecological

principle – everything depends on everything.

References

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