Transmission and effect of sublethal infection of granulosis virus (PbGV) on Pieris brassicae Linn. (Pieridae: Lepidoptera)

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 (F 1 ). The amplification of granulin gene using specific primer also showed the presence of virus in F 1 progenies of sublethally treated P. brassicae larvae, hence confirming vertical transmission.