Proc. Indian Acad. Sci. (Anim. Sci.), Vol. 95, No.2, April 1986, pp. 227-236.© Printed in India.

Host specificity of rice green leafhoppers, Nephotettix oirescens(Distant) and N. nigropictus (Stal)"

KASI VISWANATHAN and M B KALODEDirectorate of Rice Research (AICRIP), Hyderabad 500030, India

MS received 21 December 1984; revised 29 March 1985

Abstract. Intensive host range studies comprising of 55 common weeds and eight cultivatedplant species indicated that Nephotettix oirescens could survive and breed only on susceptiblerice variety, while N. niqropictus had a wider host range consisting of rice, sugarcane and fivegraminaceous weeds. N. uirescens preferred rice plant both for settling and egg laying, whileN. niqropictus showed greater preference to Leersia hexandra than others. Both speciesselected the host plants by gustation rather than by vision or olfaction.

Keywords. Host specificity; N. virescens; N. niqropictus; host selection; host range.

1. Introduction

In nature, the feeding privileges of phytophagous insects are restricted by biophysicaland/or biochemical mechanisms. An understanding of the relationship between thehost plant and insect can greatly contribute to develop pest management strategies.

The green leafhoppers, N ephotettix virescens (Distant) and N. niqropictus (Stal) havebecome one of the serious pests ofrice. Besides direct damage, both species can transmitimportant virus diseases. Thousands of hectares of rice were destroyed in 1971 and1972 by tungro virus, transmitted by N. virescens in the Philippines (IRRI 1979).

N. virescens feeds on many grasses and weeds (Alam and Islam 1959; Pathak 1968;Misra and Israel 1970; Rao and Anjaneyulu 1977). Prasada Rao and John (1974)reported that in the absence of rice, N. virescens can thrive on weeds. Alam (1974)recorded Leersia hexandra as the principal host for N. virescens. However, many ofthese studies on host range did not provide sufficient supporting data. Therefore,detailed studies were conducted on the host specificity of N. virescens and N.niqropictus and results are presented in this paper.

2. Materials and methods

2.1 Rearing and maintenance of insects

N ephotettix virescens and N. niqropictus adults were collected from experimental plotsof the All India Coordinated Rice Improvement Project. The species isolated and purecolonies were maintained in the greenhouse on potted plants of susceptible varietyTN 1 in separate cages. Rearing cages were of70 x 62 x 75 em dimension and had glasspanels on one side and the remaining sides were covered with fine nylon wiremesh.

227

228 Kasi Viswanathan and M B Kalode

2.2 Host range

Thirty two species of grasses, nine species of sedges, fourteen species of broad leavedweeds and eight cultivated plants were included for host range study (table 1). Theywere grown separately in pots and young and healthy plants were used forexperimentation. Insect survival tests were conducted by releasing ten first instarnymphs and two pairs of adults per plant separately in suitable mylar film cages. Tenplants each were used as replications in both experiments. Observations on survival

Table 1. List of plant species tested in host range studies

Plant species

WEEDSCyperaceae

Cyperus compressus Linn.e. difformis Linn.e. discans Linn. fe. rotundus Linn.Fimbristylis miliacea VahlFuirena pubescens Kunth.Kyllinga triceps Rottb.Scirpus erectus Poir.Scirpus maritimus Linn.

GramineaeAlloteropsis cimicina Stapf.Aristida hystrix Linn. fBruchiaria ramosa (L.) Stapf.B. reptans (L.) Gard. et C. L. HubbardB. mutica (Forssk) StapfChloris barbata Sw.e. »irqau: Sw.Cymbopogon caesius Stapf.Cynodon dactylon Pers.Dactyloctenium aeqyptam (L.) P. Beauw.Dichanthium aristatum (Poir) C. E. Hubb.Digitaria ci/iaris Pers.Denetra retroflex (Vaul) Pauzr.Echinochloa colonum Link.E. crusqalli Beauv.Eleusine indica Gaertn.Eraqrostis pi/osa Beauv.E. qanqetica Steud.E. tenel/a R. & S.Eraqrostielia brachyphylla Staep.Eriochloa procera Hubbard.lmperata cylindrica Beauv.Leersia hexandra Sw.Oryza officinalis Wall ex Watt.Panicum repens Linn.P. trypheron Schult.Paspalidium flauidum A. Cam.Paspalam distichum Linn.

Plant species

Perot is indicaSpordodus diander Beauv.Tripoqon roxbughianus Bhide.Urochloa panicoides P. Beauv.

AmarantaceaeAI/mania nodiflora R. Br.Amaranthus viridus Linn.Gomphrena globosa Linn.

BoraginaceaeHeliotropium panicutatum Br.

CompositaeEclipta prostrata Linn.Hymentherum tenupalium De,Laqasca mol/is Cav.Tridax procumbons Linn.

ConvolulaceaeI pomaea reptans Poir.

EuphorbiaceaeEuphorbia pilulifera Linn.

CentinaceaeEnicostema littorale BI.

LtyhraceaeAmmania baccifera Linn.

PontederiaceaeEuchomia crassipes Solms.

TyphaceaeTypha auqustata Chaub. & Bory.

CULTrVATED PLANTSGramineae

Eleusine coracana Gaertn.Oryza sativa L.Pennisecum typhoideum Rich.Saccharum officinarum Linn.Sorghum vulgare Pers.Triticum aeslivum Linn.Zea mays Linn.

LeguminosaeArachis hypogeae Linn.

Host specificity of rice green leajhoppers 229

were recorded every three days for nymphs and daily for adults. The test was repeatedfor both species by releasing 100 first instar nymphs per plant, when it was foundsuitable for either of the species. The adults thus obtained were reared further on thesame hosts for assessing their longevity and fecundity. The growth-index values werecalculated by dividing the percentage of nymphs reaching adult stage by averagedevelopmental period.

2.3 Suitability and intake offood

Suitability of different plant species as food was assessed by recording the gain in bodyweight of 100 nymphs at five-day intervals. The food intake behaviour on various hostswas studied by caging two pairs of adults per leaf for 24 hr in suitable cages andcollecting the honey dew excreted on a filter paper which was later treated withninhydrin solution. The number of probing marks produced on hosts and non-hostplants was determined by caging a single insect for 6 hr on individual leaves. Theprobing marks were stained by dipping in I %erythrosin solution.

2.4 Preference of the insects for settling and oviposition

These studies were conducted by planting selected test plants at random in a woodenflat containing puddled soil, at a spacing of 10 x 15 em. When the plants wereestablished, 200 five-day old adults were released inside the cages wherein the test plantshad been kept. The settling behaviour of the insects was studied at regular intervals andafter four days the plants were dissected to count the number ofeggs laid. Similarly, thepreference of fourth instar nymphs was also studied.

2.5 Mode offood plant selection

The role of vision was assessed by releasing adults whose eyes were closed with a thinfilm ofdark-coloured nail polish in a cage where the most preferred food plant was keptat a distance of 30 em. The movements of the insects were watched continuously for6 hr.

The importance ofantennae in food selection was studied by releasing adults (whoseantennae were removed) on the non-host plants kept on one side ofa partition cage. Onthe other side of the cage, suitable host plants were kept. After the insects settled onnon-host plants, the partition of the cage was removed and the number of insectssuccessfully reaching host plants was counted. Similar test was conducted with normalinsects.

Role of olfaction was studied by using a five-armed choice chamber. Plant leaveswere inserted into the tubes at varying lengths. Four plants were used at a time and onetube was kept blank. One hundred adults were released in the middle of the chamberand the number of insects reaching various plants and blank was recorded after 3 hr.

3. Results and discussion

3.1 Host range

N. oirescens nymphs could not survive beyond 3 days on any of the test plants exceptrice (table 2).On rice, the nymphal survival was 98 %and the adult longevity was longer

Tab

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Surv

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N.

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ant

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s

Per

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L.98

9516

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·920

5·0

15·5

14·2

108·

0O

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Wal

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22-

40-

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68·

647

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mL

inn.

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5·0

12·4

10-3

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2-9

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13-7

9·8

82·7

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Host specificity of rice green leafhoppers 231

(15,9 to 16·5 days) compared to other plant species. On the other hand, nymphs andadults of N. niqropictus survived on eight plant species for a longer period (7 to 16·3days). Chu et al (1981) reported that ratoon rice, Echinochloa crusqalli, Alopecursaequalis and Leersia hexandra were the best alternate food plants of N. cincticeps(Uhl.). An interesting aspect of the present investigation is that N. virescenscould utilisesuccessfully only the susceptible rice variety (TN 1) in host range tests both with firstinstar nymphs as well as adult insects. The high specialisation of this species(N. virescens) towards rice in the present investigation is contrary to the earlierconclusions made by Prasada Rao and John (1974) that N. virescens can feed on otherplant species including dicotyledons based on the criterion of oviposition. The abovecriterion used by these workers seems to be not appropriate since the green leafhopperadults laid few number of eggs (table 2) even on non-host plants viz. Cyperus rotundus(5),C. difformis (3),E. colonum (5)and E. crusqalli (11).Similarly, Alam (1974) based onfield observations reported hopper burn on Leersia hexandra by N. virescens while inthe present studies it was found to be unsuitable as host to this species.

Since both species laid eggs even on non-host plants under confinement (table 2)andcould survive around two days even under starvation (figure 1) it seems necessary toconsider such aspects while determining the host status of plant species against testinsect.

3.2 Host suitability

Host suitability for N. niqropictus was better on L. hexandra followed by Echinochloacrusqalli, Oryza sativa and E. colonum (table 3). However, Cynodon dactylon, Panicumrepens and Oryza officinalts were less suitable. Though the growth-index value was 1·2for Saccharum officinarum; the fecundity of the surviving insects was poor. Further theinsects which fed on L. hexandra had the highest body weight (figure 2) compared toother host plants. The insects fed on O. sativa and E. crusqalli had almost the sameweight increase after 15days closely followed by E. colonum. However, insects reared or.C. dactylon and P. repens showed lesser increase in body weight.

100...------------, 1("------------,Moist condition

Dry condition

48o96

Moist condition

----

48o

60

a'>E 100 .--------------, ,..------------,:> Dry condition

(f) 60 t\,"20 ",_

(B)After hours

(A)

Figure 1. Survival potential of adults without food. (A) N. »irescens. (B) N. niqropictus,

232 Kasi Viswanathan and M B Kalode

Table 3. Survival and development of N. nigropiclUS on selected plant species

Percentage ofsurvival after Average Average adult

days developmental longevity (days) No. ofperiod eggs Growth

Host plant 3 12 21 (days) Female Male laid index

·Oryza saliva 98 80 50 17-8 2(}5 19·0 174 2-8Oryza officina/is 90 54 6 21·2 I(}O 9·5 16 (}3Echinoch/oa c%num 95 80 52 18·5 19·5 19·0 160 2-8Echinoch/oa crusgalli 100 66 48 17·5 21·0 17'5 189 2·2Leersia hexandra 100 79 65 17·2 21·2 19'5 223 HPanicum repens 66 6 4 21·0 7·0 9·0 38 (}2Saccharum officinarum 90 54 21 18·2 12.5 1(}5 13 1·2Cynodon dacey/on 95 22 6 21·0 1(}5 11·0 21 (}3

·Variety TN I.

4

3

L. hexandra

E. crusgalliQ. sativaE. calanum----~. repens

<::: daetylon

1510After days

0'---_--__"-- ---'5

Figure 2. Extent of body weight gain by N. niqropictus in relation to different host plants.

Data on feeding behaviour showed that N. virescens, caged on host plants ofN. niqropictus, made greater number of punctures (6,6 to 12'2) in an attempt to feed onthese pfants (table 4) and also excreted less honeydew thus confirming the unsuitabilityof these test plant species to N. virescens. On the other hand, N. niqropictusmade relatively less punctures (2·g to 6'4) and deposited more honeydew while feedingon these plant species. Similar observations were reported by Naito and Masaki (1967)for N. cincticeps. Oryza sativa for N. virescens, Echinochloa colonum and Leersiahexandra for N. niqropictus were found to be most suitable hosts for feeding. Therestricted host range in case of N. oirescens could be due to the presence of somedeterrants or absence of certain stimulants needed for normal feeding in the plantspecies tested.

Host specificity of rice green leajhoppers 233

Table 4. Number of probings made by N. virescens and N. niqropictus on the leaf blades ofselected plant species

Plant species

Cynodon dactylonEchinochloa crusqalliEchinochloa colonumLeersia hexandra"Oryza sativa

Average probings/insect/hour

N. oirescens N. niqropictus

Minimum Maximum Mean Minimum Maximum Mean

9·2 14·5 11·6 3·1 7-2 6·47·4 14·0 12-2 2-8 4-6 3·15-7 8'9 7·2 2-0 3-4 2-45·0 7·6 6·6 2·0 3·1 2-82-6 4'1 3-6 3·0 6-1 4·9

"Variety TN 1.

40

~e;"0

a :§(fJ

CJ'CJ'w

80

o

80

40

•

•

•54

•

•

••

• •

4 6After hours

2

o ~. dactylol')• ~. crusgalli ISlo !",. hexondrc §

• Q. sativa IIlDA ~. repens •

o

80

40

--(1)(fJ

Ul

-40~o

Figure 3. Preference for settling and oviposition by N. uirescens on different plants.

234 Kasi Viswanathan and M B Kalode

0 ~.dadylon

• E. crusgalli !II]

80 • C. hexandra mrn0 Q. sativa ~

A ~: repens 0...

60

• • •40 • 40~ • • •z; •0 0 0 0 II 20 -"1:J II ~(]) II 0- A A A A ,I- 0 Lill. .LE...l .LE-1 .,

0 "1:J(])l/l '0l/l

l/lU 0'(]) A c;;;.. rotundus 0'l/lC 0 E. colonurn ~

wH

80 • b;, hexandra unn0 Q sativa ea• f· distichum §

• • 60• •

40 40

6 0

8 0 200 0

--b--A

0 L!..l .LL. L!-J. 00 2 4 6 24 30 48 54

After hours

Figure 4. Preference for settling and oviposition by N. niqropictus on different plants.

3.3 Host selection

Results ofmultiple choice tests with N. virescens and N. niqropictus adults are presentedin figures 3 and 4, respectively. As evident from figure 3, N. virescens was able to selectrice plant, the most preferred host, within a few hours after release and also laid a largernumber of eggs on it. The insects did alight on non-hosts, but little time was needed toreject such plants. However, the insects laid some eggs even on non-hosts.

Since a greater number of host plants of N. niqropictus were in the tests with thisspecies, the high preference was not apparent until 24 hr. However, after this periodL. hexandra was found to be the most preferred host by this species. In general, a largernumber of eggs were also noticed on L. hexandra followed by O. sativa (TN 1),E. crusqalli and E. colonum (figure 4). In separate studies nymphs of both species werealso found to locate their suitable hosts within a few hours after release.

Host specificity of rice green leafhoppers 235

It was observed that vision is important only for settling (table 5)and not involved inthe actual selection process. However, in some other insects visual stimuli are involvedin the behavioural responses before alighting. Olfaction also appeared to have nosignificant role in selecting suitable hosts as indicated both in the tests with antennaeremoved insects (table 6) and in choice chamber tests. This is further supported byprobing behaviour studies where the insects made punctures even on non-host plants.Thomas (1972) also found that the beet leafhopper Circulifer tenellus was unable todiscriminate between any preferred and non-preferred species until the feedingoccurred. According to Sogawa (1973) the brown planthopper also seemed to localisethe sucking tissues by random exploratory probings. Therefore, similar to many otherinsects, the host selection by rice green leafhoppers in the present study is ofchemosensory nature and principally by gustatory stimuli.

The foregoing discussion on host specificity suggests a restricted host range ofN. virescens and highly specialised compared to N. niqropictus which seems to beoligophagous. However, further critical studies are necessary in different agro-climaticzones by testing large number of plant species from the local flora to get additionalinformation, particularly for N. virescens being the vector of tungro virus disease.

Table 5. Role of vision in host selection by N. uirescens andN. niqropictus

Percentage of insects settled on host plantshours after release

Insects 3 hr 6 hr 8 hr

N. »irescens"Normal 15 35 89Eyes closed 0 0 0

N. niqropictus'"Normal 21 47 75Eyes closed 0 0 0

Host plants: ·Oryza sativa (TN I) ..Leersia hexandra

Table 6. Role of antennae in host selection by N. virescens and N.niqropictus

Percentage of insects settled

With antennae Without antennae

Insect Host 24 hr 48 hr

N. »irescens ·0. sativa 88 96N. niqropictus L hexandra 71 90

"Variety TN 1.

24 hr

7670

48 hr

9179

236 Kasi Viswanathan and M B Kalode

Acknowledgement

This paper is part of the Ph.D. Thesis submitted by KV. The authors are thankful toDrs S V S Shastry and W H Freeman for encouragement.

References

Alam S 1974 Recent ecological studies in rice insects -leafhoppers and planthoppers, (Mimeo.); InternationalRice Research Conference, 1974, IRRI, April 24, P 3

Alam Z and Islam A 1959 Biology of the rice leafhopper, N ephotettix bipunetatus Fab. in East Pakistan; Pak.J. Sci. Res. 2 20-28 •

Chu Y I, Liou R F and Mu T 1981 Evaluation ofgraminaceous plants as overwintering host plants of greenrice leafhopper iNephotettix cincticeps Uhler); Plant Prot. Bull. Taiwan 23 235-242

IRRI (International Rice Research Institute) 1979 IRRIlong range planning Committee report; Los Banos,Laguna, Philippines 91 p

Naito A and Masaki J 1967 Studies on the feeding behaviour of green rice leafhopper, N ephotettix cincticepsUhler. II. Probing frequency of the adult leafhopper (In Japanese with English summary); Jpn J. Appl.Ent. Zool. II 150-6

Misra B C and Israel P 1970 The leaf and planthopper problems in high yielding varieties of rice; Oryza 7127-30

Pathak M D 1968 Ecology of common insect pests of rice; Annu. Rev. Entomol. 15 257-94Prasada Rao R D V J and John V T 1974 Alternate host of rice tungro virus and its vector; Plant Dis. Reptr. 58

856--60Rao G M and Anjaneyulu A 1977 Alternate host of rice tungro virus and its vectors; IRRN 2 15Sogawa K 1973 Feeding behaviour of the brown planthopper and brown planthopper resistance of indica

rice Mudgo; Bull. No.4, Lab. Appl. Ent. Fac. Agr. Nagoya Univ. p 151Thomas P E 1972 Mode ofexpression ofhost preference by Circulifer tenellus, the vector ofcurly top virus; J.

Eeon. Ent. 65 119--23