The Effects of Sublethal Dose of Nuclear Polyhedrosis Virus on the Development, Fecundity and Progeny of the American Bollworm, Heliothis armigera (Hubner)

Abstract

The results of the bioassay study indicated that the median lethal dose (LD50) of the nuclear polyhedrosis virus (NPV) of the American bollworm, Heliothis armigera (Hubner), was 1.94 x 10³ PIBs/larva and the sublethal dose was 5.187 PIBs/larva. There was no significant difference between those worms infected with a sublethal dose and the healthy control group in terms of larval age, pupal age, and pupal and adult weight. However, there was a significant difference among the two groups at the adult stage. Pupa an adults infected with a sublethal dose of the NPV were shown to be morphologically similar in shape and size to those of the control group. However, it was found that with a sublethal dose pupation decreased by 20% and adult male and female emergence decreased by 38% and 29% respectively. The male and female ratio of pupa and adult of those infected with a sublethal dose and the healthy control group were similar. The sublethal dose of the NPV had considerable effects on the progeny of the American bollworm. It was found that the number of eggs per female decreased 60.13%, egg hatching decreased 33%, and egg interval decreased from 2.60-5.00 to 2.40-3.80 days. In addition, this virus can be transmitted to the progeny 54.54% of the time. The results suggest that a low dosage of NPV had significant effects on the American bollworm and their progeny. These effects are very important in determining the value of this virus as a microbial control agent of H. armigera.