A granulosis virus strain infecting Pieris brassicae (PbGV) was isolated from the dry temperate region of northwestern Himalayas as a potential microbial agent for its management. The effect of different botanicals (having insecticidal action against P. brassicae) on the bioefficacy of PbGV was evaluated under laboratory conditions using leaf disc bioassays on cabbage for improving the insecticidal performance of the PbGV. The synergistic action of different botanical extracts was evident in terms of reduction in LC 50 values against different botanical extracts. Among different extracts, petroleum-ether extract of neem seed kernel (NSK) when combined with PbGV resulted in maximum reduction of LC 50 value (4.39×10 2 occlusion bodies [OBs] ml −1 ) followed by methanolic extract (7.38×10 2 OBs ml −1 ) and aqueous extract (9.36×10 3 OBs ml −1 ) as compared with PbGV alone (1.85×10 4 OBs ml −1 ) for 2nd instar larvae of the test insect. These trends were found analogous in cases of 3rd and 4th instars of P. brassicae with different solvent extracts of NSK. The other botanicals evaluated, viz., Eupatorium and Artemesia, also resulted in reduction of LC 50 values for 2nd, 3rd and 4th instars as compared with PbGV alone when different extracts were combined with virus for bioassays. The studies suggest that the PbGV in combination with botanical pesticides could be more useful as a bio-pesticide against cabbage butterfly (P. brassicae) in IPM programs.
A strain of granulosis virus from Pieris brassicae (Linn.) was isolated and characterized from the dry temperate region of Himachal Pradesh, India situated at an altitude of 2580 m above msl. The pest appears in the region during the summer months (May to September) and overwinters as pupae during the snow covered winter months. Carry over of virus inoculum as sublethal infections, could be an important mechanism for next season epidemics in the region. Effect of sublethal P. brassicae granulovirus infection on its host was therefore studied to understand the transmission mechanism. The third instar larvae were exposed to sublethal viral infection. The surviving larvae showed symptoms of virosis in the pupal and adult stages. The per cent pupation and adult emergence of sublethally infected larvae were significantly reduced and no adult emerged from the abnormal pupae. The mode of transmission of viruses from parents to offspring appeared to be through eggs (transovum). The emerging larvae from the eggs laid by treated females also showed symptoms of virosis. Complete mortality due to viral infection was observed at third instar stage in the offspring (F1). The amplification of granulin gene using specific primer also showed the presence of virus in F1 progenies of sublethally treated P. brassicae larvae, hence confirming vertical transmission.
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