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Laboratory and field evaluations of the efficacy of a fast-killing baculovirus isolate from Spodoptera frugiperda

Behle, Robert W., Popham, Holly J.R.
Journal of invertebrate pathology 2012 v.109 no.2 pp. 194
Brassica oleracea var. capitata, Spodoptera frugiperda, Spodoptera frugiperda multiple nucleopolyhedrovirus, application rate, bioassays, cabbage, death, encapsulation, half life, insecticidal properties, larvae, leaves, lignin, mortality, solar radiation, viral insecticides
Three biopesticide parameters were evaluated for a fast-killing isolate (3AP2) and a wild-type isolate (Sf3) of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV). Both isolates were evaluated for virus production using in vivo methods, for speed of kill based on bioassay of applications to glasshouse-grown and field-grown plants, and for residual insecticidal activity of unformulated virus and an encapsulating formulation to provide UV protection. Two inoculation rates comparing relative in vivo production of the isolates demonstrated 3AP2 inoculated larvae were significantly smaller than Sf3 inoculated larvae at death. At the lower inoculation rate, Sf3 inoculated larvae produced approximately twofold more occlusion bodies as the 3AP2 inoculated larvae. A model system of applications to cabbage plants and a bioassay to observe mortality of neonate S. frugiperda (J.E. Smith) after feeding on samples of treated leaves was used to evaluate speed of kill and residual insecticidal activity. The LT₅₀ for the 3AP2 isolate was at least 30h less than the LT₅₀ for the Sf3 isolate when applied to either glasshouse-grown or field-grown plants. The spray-dried lignin encapsulating formulation provided similar benefits to both virus isolates when exposed to simulated sunlight in the laboratory and to natural sunlight in the field. For treatment applications to field grown cabbage in June, the half-life for efficacy of unformulated virus was <7.5h compared with a half-life of >26.7h for encapsulated virus. These results demonstrate that improved technologies can be combined to address characteristics which otherwise can limit the commercial potential of microbial-based biological insecticides.