Indian Journal of Experimental Biology Vol. 41, April 2003, pp. 379-382 Modified behaviour in nucleopolyhedro virus infected field bean pod borer, Adisura atkinsoni and its impact on assessing the field efficacy of NPV K Narayanan Project Directorate of Biological Control, Hebbal, Bangalore 560 024, India Received 31 October 2002; revised 4 February 2003 When nucleopolyhedro virus of A.atkinsoni was applied at 250 LEtha, there was no significant difference between the viruses treated and control plots with regard to the total number of live larvae feeding outside the pod. However, due to changes in behaviour in NPV infected A. atkinsoni by way of coming out of the pod, there was a significant difference when counts were taken with regard to total number of larvae found feeding inside the pod. Both endosulfan at (0.07%) and virus (125 LEtha) in combination with endosulfan (0.035%) significantly reduced the larval population of A. atkinsoni and Sphaenarches anisodactylus. There was no significant difference between the virus and control plots with regard to percent­ age of pod damage. However, when the yield was assessed based on the seed weight, there was significant difference. Observations on the microbial control of certain insect system, based on the modified behaviour of NPY in­ pests with the nucleopolyhedro virus (NPV) have re­ fected A.atkinsoni has been reported and discussed. vealed that the normal physiology and behavior of the Although number of pod borers are reported to insects may change suddenly, thereby posing some cause damage, the field bean crop, the Indian bean limjtations in determining their effectiveness on par (Dolichos lab lab) variety, Hebbal avarai 3, was se­ with chemical pesticides. For example bacterial verely affected both by A. atkinsoni and plume moth, pathogens like B. thuringiensis; determining its effec­ Sphaenarches anisodactylus, during the period under tiveness and usefulness were not difficult since it has study. Since the NPV of A.atkinsoni was found to be a very quick knock-down effect. But the past experi­ specific and not cross infective to S. anisodactylus, a ence with certain insect viruses especially nucleo field trial was conducted with following treatments polyhedro viruses was erratic about their perform­ viz. virus @ 250 LElha (l LE = larval equivalent ance. This was apparent from the control of cabbage =6x 109 polyhedral occlusion bodies (POB's); virus looper' with its nucleopolyhedro virus. Since the cat­ @ 125 LElha + endosulfan 0.035% and endosulfan erpillars feeds externally on the foliage. But with 0.07% which were randomized and replicated five NPV isolated from internal borer like Heliothis spp., times. The virus for the treatments was propagated in the results were found to be erratic. In some tests it A. atkinsoni larvae, reared on artificial diets. Observa­ was found to be better2 and in some tests it was mar­ tions on infestations were based on the number of 3 ginal . This may be partly due to the improper timing healthy and diseased larvae present. To assess the of virus application against the target insect. It may damage, pod counts were taken. Yield data were re­ partly due to the lack of understanding on insect­ corded based on the basis of seed weight. virus-plant relationship, before and after infection Larval population - There was no significant dif­ involving feeding behaviour while assessing its effi­ ference in virus alone treated plot and control plots cacy. Though the occurrence of a nucleopolyhedro with regard to the number of live larvae of A. atkil1- virus (NPV) of field bean podborer, Adisura alkinsolli soni present on the entire plant surface, including foli­ 4 has been reported in India , no further study has been age, flower and outside the pod (Table 1). However, conducted on the host- pathogen relationship. In the there was a significant difference between endosulfan present paper, the results of the field efficacy of NPY treated at 0.07%, concentration as well as at its re­ of A. atkinsoni on field beans pest management duced dose of 0.035% concentration in combination with virus at 125 LE/ha. As demonstrated in many 2 6 previous tests . and corroborated again herein, the E-mail: kn_pdbc @rediffmail.coI11 Phone: 080-351 1982-40 (0) larval counts which are routinely used to compare Fax: 080-341 1961 chemical insecticide treatments were not good 380 INDIAN 1 EXP SIOL, APRIL 2003 estimate of the effectiveness of a viral biopesticide. geotropism and moved to the top of the plant just This may be due to the inclusion of even living in­ prior to death. Death occurred generally over the fected larvae in the larval population counts. foliage, flower bud or pod after developing typical Eventhough, there was no significant difference wilt symptoms as in the case of any other virus between the virus alone treated and control plots with infected lepidopterous larvae. This phenomenon regard to the number of live larvae of A. atkinsoni exhibited by the NPV-infected A.atkinsoni which present outside the pod on the plant surface, nearly 32 necessitated to make further obsevation on the number to 48% diseased incidence of NPV was noticed in of larvae present inside the pod. For this total number virus alone treated and virus plus insecticides treated of A. atkinsoni larvae present inside the ten pods plots. It is well known that insects exhibit a variety of selected at random per replication was made. physiological, morphological and behavioural re­ Evidently, it was found that all the treatments were sponses to infection, which can affect both pathogen significantly superior to control (Table 2). and host fitness. Normal behaviour of certain insects It is evident from the present field observation as may change suddenly when they become infected well as from the study of Govindan8 that A. atkinsoni with a virus disease. A classical example is that of the larva mostly behaves as a true internal pod borer, larvae of nun-moth Lymantria l11 onacha, which gather unlike that of Heliothis larva. Hence, significant effect at the top of the trees in groups when infected with the of virus was well pronounced in the present experi­ "wipfelkrankheit virus" (tree top disease virus)7. ment when it was assessed based on the larvae present Further, it was observed that under field condition, the inside the pod instead of outside taking into consid­ virus infected A.atkinsoni larvae showed negative eration of its change in feeding behaviour after the infection by NPV. Similar change in the feeding be­ Table I - Effect of NPY, NPY plus insecticide combination and haviour of cabbage moth, Mamestra brassicae by way insecticide alone on (A. atkinsoni & S. anisodactyills) total live of becoming restless and dispersing more widely than larvae and apparently healthy population count of A. atkinsoni 9 healthy has been reported by Entwistle • Such behav­ and S. anisodactyills ioural modification may have been arisen to benefit Treatments Adisura atkinsol1i S.anisodactylus either the host or the pathogen. This behaviour Total Apparently exposes the infected insects to predators and other live healthy larvae larvae dispersed agents. This dispersal behaviour by infected insects allows for a wider distribution of pathogens7. TI NPY @ 250 LElha 9.25 6.06 5.65 For instance, Helicoverpa armigera and Spodoptera (0.94) (0.75) (0.65) T2 NPY @ 125 LE + 4.00 3.93 litura larvae go to higher elevation for the sake of Endosulfan 0.035% (0.54) (0.54) (0.30) oxygen requirement as a result of being infected with TJ Endosulfan 0.07% 5.45 4.93 0.10 their respective NPVs'o. Further, the low level of (0.72) (0.69) (-9.30) A. atkinsoni incidence observed in virus plus endosulfan T4 Control 11.15 11 .06 4.70 (1.0 I) ( 1.02) (0.65) treated plot may be due to their combined effect, since (Figures in parantheses are transformed values) the virus infected larvae of A. atkinsoni started showing C. D. (P=0.015) 0. 17 0.14 0.14 the classical change in their behavioural abnormality Table 2 - Effect of NPY, NPY plus insecticides combinations and insecticide alone on the live larval population of Adisllra atkinsoni in side and outside the pod and pod damage Treatments Mean larvae/eod Total outside Pod damage Outside the pod Inside the pod + inside (%) TI NPY @ 250 LE/ha 0.24 0.70 0.46 38.53 (0.44) (0.85) (0.67) (38.28) T2 NPY @ 125 LE/hu+ 0.14 0.52 0.38 25.83 Endosulfan 0.035% (0.26) (0.75) (0.60) (30.13) TJ Endosulfan 0.07% 0.02 0.36 0.34 31 .60 (0.20) (0.59) (0.57) (32.66) T4 Control 0.30 1.68 1.38 48.64 (0.52) ( 1.22) (1.14) (40.60) (Figures in parantheses arc transformed values) C.D. (P=0.05) 0.22 0.24 0.22 2.83 NOTES 381 by way of coming out from the pod and thereby pre­ Table 3 - Effect of NPV, NPV + insecticide combination and dispose themselves to the contact effect of endosulfan insecticide alone on grain yield during its subsequent treatments. There are reports Treatments Grain yield g/plant that chemical insecticide (here endosulfan) weakens b T J NPV @ 250 LEtha 51.30 a the host tolerance to facilitate viral infection and simi­ T 2 NPV @ 125 LE +Endosulfan 0.035% I 36.26 larly there are also report that viral infection weakens T3 Endosulfan 0.07% 142.98a c the tolerance of the insect or predispose to insecti­ T 4 Controi 11.70 cides II. Further the study on the combined action of In a vertical column means followed by similar letters are not , 12 NPV of Mythimna separata with endosulfan and different statistically (P = 0.05) by L.S.D.