Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2011
Publication Date: 2/2/2012
Citation: Behle, R.W., Popham, H.J. 2012. Laboratory and field evaluations for efficacy of a fast-killing baculovirus isolate from Spodoptera frugiperda. Journal of Invertebrate Pathology. 109:194-200.
Interpretive Summary: Commercial development of baculovirus-based biological insecticides as a "green" technology for pest control has been hindered by their slow speed of kill, short residual activity after application, and high production costs. A recently discovered isolate of the baculovirus pathogen of the fall armyworm is known to kill pest larvae faster than previous isolates in the laboratory experiments. This research demonstrated that in vivo production of this fast-killing isolate was slightly less than wild-type baculovirus, but the faster speed of kill was maintained when applied to plants, and residual activity in the field was greatly extended with an encapsulating formulation. The results show the benefits of combining diverse technologies for three important attributes necessary for the successful development of a microbial-based biological insecticide and are expected to garner additional research and commercial interest.
Technical Abstract: Three biopesticide parameters were evaluated for a fast-killing isolate (3AP2) Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) and a wild-type isolate (Sf3) of the same baculovirus. 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 ultraviolet (UV) protection. Two inoculation rates comparing relative in vivo production of the isolates demonstrated 3AP2 infected larvae to be significantly smaller than Sf3 infected larvae at death. At the lower inoculation rate, Sf3 infected larvae produced approximately two-fold more polyhedra as the 3AP2 infected larvae. A model system of applications to cabbage plants and a bioassay to observe mortality of neonate Spodoptera frugiperda (J. E. Smith) after feeding on samples of treated leaves was used to evaluate speed of kill and residual insecticidal activity. The calculated LT50 for the 3AP2 isolate was at least 30 h less than the LT50 estimate 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 in June to field grown cabbage, the half-life for efficacy of unformulated virus was <7.5 h compared with a half-life of >26.7 for encapsulated virus. These results demonstrate that improved technologies combine easily to address characteristics which otherwise can limit the commercial potential of microbial-based biological insecticides.