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Pathogenicity of Spodoptera Litura Nuclear Polyhedrosis Virus to S. Litura F. Larvae and its Impact on Sycanus Leucomesus W
Thesis Abstract:
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 108 PIBs/larva. Bioassay results showed that LD50, LD90, and LD99 were 5.50 x 104, 5.26 x 108, and 9.26 x 1011 PIBs/larva, respectively. The regression equation, Y = 3.47 + 0.32X, indicated that an increase of larval mortality was due to an increase in viral doses. The lethal time (LT) of the doses was eight, six, and five days, respectively, with a regression equation of Y = 13.59-9.41 X.
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 with 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 1010 PIBs. The infectivity of the defecated NPV was comparable with that of the virus isolated directly from S. litura larvae. Both isolates could cause 96 percent larval mortality.
