Affectivity of Spodoptera littoralis nucleopolyhedrovirus (SpliNPV) against first and second instar larvae of the cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Preliminary bioassays were conducted to determine the virus activity against the 1st and 2nd instar larvae of the cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae). First instar larvae were more susceptible to the virus than the second instar larvae. Mortality response of the larvae was greater at the highest concentration of the virus than at lowest concentrations. The lethal concentration that killed 95% of the tested larvae (LC95%) was 2.32 x 106. The obtained mortality rates of S. littoralis first instar (1st) larvae were 0, 15.15, 16.77, 43.57, 82.44 and 96.94%, for the tested concentrations of control (2 x 102, 2 x 103, 2 x 104, 2 x 105 and 2 x 106 PIB/ml). However, second instar (2nd) larvae were less susceptible to the virus than the first instar larvae with the mortality rate of 0, 4, 9.39, 25.33, 43.24, and 71.63%, for the same tested concentrations, respectively. In control treatment, no mortality was recorded. The high concentration levels caused a high rate of mortality. The same trend of mortality is similar to those found by other studies. Key words: Biological control, virus, SpliMNPV, Noctuidae, cotton leafworm, Spodoptera littoralis.