Author : James Rubinsin Kotulai

Summary : Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is a pest of many agriculture and forestry crops in several parts of the world, including Malaysia. One of the natural enemies responsible for regulating field population of S. litura is a nuclear polyhedrosis virus (NPV). In this study, the S. litura NPV was tested for its actual pathogenicity to S. litura larvae using eight viral doses ranging from 60 to 6 x 10 (superscript 8) PIBs/larva. Bioassay results showed that LD (subscript 50), LD (subscript 90), and LD (subscript 99) was 5.50 x 10 (superscipt 4), 5.26 x 10 (superscript 8) and 9.26 x 10 (superscript 11) PIBs/larva, respectively. The regression equation, Y = 3.47 + 0.32X, indicates that an increase of larval mortality was due an increase in viral doses. The LT of the doses was eight, six, and five days, respectively, with a regression equation of Y = 13.59-9.41X. The NPV impact on the predator Sycanus leucomesus Walker (Hemiptera: Reduviidae) was studied by providing either healthy or NPV-infected prey. The survival rate of the predator that fed on infected prey was critical during the first instar. However, the developmental time was not affected even though the length of tibia and width of head capsule were significantly reduced. The preoviposition period of the female predator fed infected prey was 12 days longer and the fecundity rate was reduced by 41 percent. The longevity of adults was also significantly shortened. A single deposit of S. leucomesus excreta contained 1.42 x 10 (superscript 10) PIBs. The infectivity of the defecated NPV was comparable to that of the virus isolated directly from S. litura larvae. Both isolates could cause 96 larval mortality.