Biological activity of Pakistani isolate SpltNPV-Pak-BNG in second, third and fourth instar larvae of the leafworm Spodoptera litura

Recently, a novel isolate of the baculovirus Spodoptera litura nucleopolyhedrovirus (SpltNPV) has been isolated from Pakistan, which is distinct from the type species SpltNPV-G2 (ICTV). Here, we examined the biological activity of this isolate (SpltNPV-Pak-BNG) in second (L2), third (L3) and fourth instar (L4) larvae of the leafworm S. litura, more specifically to measure biological properties that are relevant for use of this virus for pest control under field conditions. The median lethal dose for L2 and L3 instar larvae was similar, but significantly lower than for L4 larvae. Likewise, the survival time was similar for L2 and L3 larvae (84 h), but was significantly longer for L4 instar larvae (108 h). Thus, in terms of efficacy, S. litura L2 and L3 instar larvae are the preferred targets for S. litura control with SpltNPV-Pak-BNG in field crops in Pakistan. On the basis of our data spray regimes can be designed to control the leafworm in cotton and vegetable crops targeting L2 and L3 larvae.