An assassin bug, Sycanus leucomesus Walk. (Hem., Reduviidae) fed on nuclear polyhedrosis virus (NPV)‐infected larvae of Spodoptera litura Fabr. (Lep., Noctuidae) inflicted variable effect on its developmental biology. The impact varied with the duration the predators were exposed. The predators that were fed infected prey throughout their lives appeared normal but they had significantly smaller sizes of head capsules and shorter tibial lengths than those fed healthy prey. These individuals had their overall pre‐imaginal survival rate reduced by 10% from 91.25 to 81.25%, pre‐oviposition period prolonged to more than 12 days, longevity reduced by 10 and 19 days in the males and females, respectively, and fecundity reduced to 41%. Even though ingestion of NPV could adversely influence their biology, the predators could serve as disseminators of the pathogen. The predators defecated infective viral polyhedral inclusion bodies (PIBs) ranging from 1.22 to 1.60 × 1010/deposit with an average of 1.42 × 1010. This NPV, when fed to its original host, caused 97% larval mortality within 10 days. Thus in nature, S. leucomesus may suppress the pest population not only by predation but also by dispersing the pathogen.

The effects of pH, sunlight and rearing temperature on infectivity of nucleopolyhedrovirus (SpltNPV) were investigated against larvae of Spodoptera litura (Fabricius). The infectivity of virus increased with increased larval rearing temperature. The LT 50 values were significantly reduced from 24 to 6 days when rearing temperature was increased from 20 to 35 8C. The pH of the substrate significantly affected the infectivity of the virus. The LT 50 values increased to about fourfold when the pH of suspension was raised from 7 to 11. Infectivity of the virus was more adversely affected in alkaline than in acidic suspension. Sunlight also deleteriously affected infectivity of the virus. The LT 50 values increased with the increase in the period of sunlight exposure. A complete viral inactivation occurred after 12 h of direct sunlight exposure.

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