EFFICACY AND VIRULENCE OF Spodoptera littoralis NUCLEOPOLYHEDROVIRUS on S. littoralis LARVAL FEEDING AND SUSCEPTIBILITY

Abstract

Entomopathogenic baculoviruses have long been recognized as vital environmentally safe alternatives to chemical pesticides. A study for investigating the virulence and susceptibility of Spodoptera littoralis larvae to S. littoralis nucleopolyhedrovirus (SpliNPV) isolate was carried out. Bioassay experiments on the 1st and 2nd larval instars using droplet feeding method revealed that polyhedral for 50% or 90% mortality of the 2nd larval instar of S. littoralis was significantly lower compared with the 1st instar. While, the 1st instar was killed faster than the 2nd one especially with the higher concentration. The susceptibility of the infected 2nd instar when feeding on different hosts showed that larvae were more susceptible when feeding on eggplant leaves followed by lettuce leaves, artificial diet and tomato leaves as shown by larval weight and reduction in feeding. The reduction in both larval weight and feeding were significantly higher with 1x107 PIB/ml than 1x104 PIB/ml in the majority of cases. S. littoralis larvae showed more than 2 times of tolerant to the 3rd passage of SpliNPV on the level of LC50 and more than 18 times tolerant on the level of LC90. The tolerant levels of S. littoralis larvae for the 3rd passage of virus was associated with more than 20% increase in time taken for kill with no changes in DNA patterns regarding subsequent passages in S. littoralis larvae using a restriction enzyme EcoRI.