Indian Journal of Experimental Biology Vol. 44, May 2006, pp. 419-421

Cross infectivity of baculovirus, Spilarctia nuclear polyhedrosis virus (SoNPV) against caterpillars obliqua nuclear polyhedrosis virus against of P. xanthorrhoea and S. obliqua. mulberry pest, Porthesia xanthorrhoea Kollar Polyhedral Occlusion Bodies (POBs) of SoNPV were purified from the field infected caterpillars of S. R Varatharajan*, M Ingobi Singh & LReeta** obliqua following the protocol provided by Sudhakar 8 Department of Life Sciences, Manipur University, et al . Different concentrations of the pathogenic Imphal 795 003, India suspension of SoNPV were prepared from the stock solution by diluting appropriately with water and Received 8 November 2005; revised 3 March 2006 counting the POB with conventional 9 Spilarctia obliqua nucleopolyhedrosis virus (SoNPV) has been haemocytometer . There were 6 concentrations and rd found effective against S. obliqua (Walker) as well as Porthesia each one replicated thrice. Thirty larvae (3 instar) xanthorrhoea Kollar. LC50 concentration of S. obliqua SoNPV each of S. obliqua and P. xanthorrhoea were used per 4 4 against S. obliqua and P. xanthorrhoea was 2.5×10 and 3.7×10 treatment separately @ 10 larvae/ replication. The POBs/ml, respectively. LT50 of SoNPV against S. obliqua was 5.73 larvae were individually inoculated with SoNPV by days, while it was 6.98 days for P. xanthorrhoea. Cross infectivity 9,10 of SoNPV against P. xanthorrhoea and ease of its mass production leaf disc method . From each mulberry leaf, circular may make it an ideal biopesticide. disc of 4cm diameter was cut along with the petiole. Keywords: Baculovirus, Microbial control, Mulberry pest, Five μl of respective concentration of SoNPV Nuclear polyhedrosis virus, Porthesia xanthorrhoea, suspension was spread on each leaf disc and on air Spilarctia obliqua drying, each leaf disc was provided to each larva in an Spilarctia obliqua (Walker) (Arctiidae: Lepidoptera) individual culture, which was maintained in a small and Porthesia xanthorrhoea Kollar (Lymantridae: petri plate (8.5cm diam.) under laboratory conditions Lepidoptera) are important pests of mulberry plant1-3. of 29 º± 2ºC and RH 60 ± 5% for 8-12 h. On complete Both the caterpillars are gregarious and active during feeding the leaf disc, larvae under each group of June to September under the climatic conditions of replication were reared on fresh mulberry foliage in Manipur, North-East India. They infest many plants glass jars (16×8 cm) with 10 individuals each. Fresh like pulses, oilseeds, cereals and certain vegetable foliage was provided everyday and observation on 4 their mortality rate was taken daily and the data were crops by virtue of polyphagous habit . It has been 11 processed for LC50 using probit analysis . reported that a single larva of S. obliqua consumes rd about 1200 g of mulberry leaf during its entire larval In order to calculate LT50 of SoNPV, 3 instar larvae period5 as a consequence; S. obliqua can cause a total of S. obliqua and P. xanthorrhoea were inoculated with foliage crop loss of about 4.9%6. Although Oak tasar the polyhedra of SoNPV at their respective LC50 dose culture is predominantly practiced in Manipur, at obtained in the above experiment. Sixty larvae each of present much attention is focused on mulberry in view the two pests were inoculated and reared as per the of the influence of Indo-Japanese project in which the procedure stated above with 20 individuals per Japanese Government has agreed to support to the tune replication. In addition, SoNPV obtained from P. of Rs.450 crore7. Under such condition, more area will xanthorrhoea was once again tested against the be brought under mulberry cultivation, enabling the caterpillars of S. obliqua by inoculating them with 5 minor pests to stabilize their population so as to reach 5×10 POB/ml. This reciprocal inoculation study was still higher density. Therefore, to keep the pests under carried out with the aim to confirm the cross infectivity check, adequate protection using eco-friendly approach of the pathogen, SoNPV. The data thus obtained on becomes imperative. Keeping this in mind, the present time factor versus mortality rate were separately processed for probit analysis11. study was attempted to evaluate the effect of S. obliqua The mortality rate of caterpillars showed a rising ______*Correspondent author. ([email protected]) trend on larval death with increasing dose of ** Present address⎯Regional Tasar Research Station, Central polyhedra, thereby indicating a dose dependent rd Silk Board, Imphal relation. Some of the larvae stopped feeding on the 3 420 INDIAN J EXP BIOL, MAY 2006

Table 1⎯Comparative susceptibility of S. obliqua and P. xanthorrhoea to SoNPV rd 2 Target pest (3 instar) Chi-square (X ) Regression equation LC50 & Fiducial limit OBs/ml LT50 4 4 Spilarctia obliqua 29.3 Y = 1.54+0.8x LC50 = 2.5x10 L = 1.9x10 U = 3.2x104 4 3 Porthesia xanthorrhoea 19.7 Y = 3.31+0.4x LC50 = 3.7x10 L= 6.3x10 U= 2.3x105 Spilarctia obliqua 25.9 Y = 9.4(x)-2.2 LT50 L = 5.23 5.73 days U= 6.24 Porthesia xanthorrhoea 30.4 Y = 14.2(x)-6 LT50 L= 6.32 6.98 days U = 7.70

LC50 is expressed in OBs/ml. LT50-in days. L = Lower limit and U = Upper limit LT50 is based on the LC 50 value of SoNPV obtained for the respective species. day and died on the 5th day, but mortality (100%) was Ipomoea cornea23. Now, as an alternate host, P. noticed on 12th day in all the virus inoculated cultures. xanthorrhoea can also be used for SoNPV The LT50 of SoNPV against S. obliqua and P. augmentation by way of rearing the larvae on even xanthorrhoea was 5.73 and 6.98 days, while the LC50 non-mulberry plants due to its polyphagous habit. value was 2.5×104 and 3.7×104 POB/ml, respectively This may, possibly, improve further virulence of the (Table 1). The reciprocal inoculation of S. obliqua virus due to serial passage through heterologous host24. with the SoNPV obtained from P. xanthorrhoea Therefore, in view of safety of SoNPV to silkworm, its indicated its LT50 as 6.45 days with the fiducial limit ease rearing and infectivity to pest species, it is of 5.77 to 7.23 days, X2 = 41.7966 and regression possible to use SoNPV as an effective, eco-friendly value Y=14.170(x)-6. The larvae exhibited symptoms bio-pesticide against S. obliqua and P. xanthorrhoea. of polyhedrosis such as restless movement, shiny This work was carried out during the tenure of the loose cuticle, oozing of haemolymph and eventually DBT project. Authors thank DBT, New Delhi for the hanging upside down with their caudal legs. In financial support and Manipur University for the basic general, baculovirus has very restricted host range and facilities and Central Silk Board for the mostly species specific12, with exception like that of encouragement. Autographa californica NPV which is capable of infecting nearly 30 insect hosts13. Similarly, NPVs of References Anagrapha falcifera, Mamestra brassicae and 1 Anonymous, Handbook on pest and disease control of mulberry and silkworm. (United Nations Economic and Galleria mellonella have also been reported to have 14,15 Social Commission for Asia and the Pacific, Thailand) 1990, many lepidopteran hosts and within the order 87. Lepidoptera16. Such features like specificity and 2 Vineet kumar, Gupta V P, Sarkar A, Babu A M & Datta R K, safety to non-target/beneficial organism,17-18 make Pathogenicity & Polyhedra morphology of Spilarctia obliqua them desirable for pest control programmes19-21. nuclear polyhedrosis virus, Int J Indust. Entomol, 1 (2000) 177. In the present study, the occlusion bodies of 3 Varatharajan R, In vivo production of SoNPV through the rd th SoNPV were also fed to the 3 and 4 instar larvae of caterpillars of Spilarctia obliqua (Walker), (DBT Project- Bombyx mori by surface contaminating22 the mulberry Final Technical Report, Submitted to Department of leaf with SoNPV @ 2×1012 POB/ml. The inoculated Biotechnology, New Delhi) 2004, 30. 4 Singh Y R & Varatharajan R, Infestation level of Spilosoma larvae of B. mori (race ka × Ma) did not show any obliqua (Walker) (Arctiidae: Lepidoptera) on certain crops in symptoms of viral infection, rather all the worms Imphal valley of Manipur, Indian J Agric Sci, 75 (2005) 61. (n=150) entered into cocoon and emerged in to 5 Sharma B & Tara J S, Comparison of consumption and normal adult. Similar treatment of SoNPV did not utilization of mulberry leaves in two moths–Spodoptera littura (Fab.) and Diacrisia obliqua Walker, Indian J affect the Oak tasar silkworm, Antheraea proylei. Entomol, 50 (1988) 336. Since, both the species of silkworms indicated a 6 Shree M P & Manjunatha S, Incidence of Bihar hairy negative response to SoNPV, this viral pesticide could caterpillar (Spilarctia obliqua) in a mulberry garden, Indian J be used for field use particularly in the mulberry Sericult, 37 (1998) 174. 7 Anonymous, Manipur Sericulture project – Revised definite garden. Further, technique to augment the polyhedra overall development and implementation plan, abridged of SoNPV through in vivo method has already been version (Government of Manipur, Manipur State, Imphal) standardized by rearing S. obliqua larvae on the weed 2003, 44. SHORT COMMUNICATION 421

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