Comparative activity of commercial baculovirus formulations against heliothine pests of cotton

Authors: Little, Nathan; Luttrell, Randall; Mullen, Regina; Allen, Clint; Parys, Katherine

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2018
Publication Date: 3/21/2019
Citation: Little, N., Luttrell, R.G., Mullen, R.M., Allen, K.C., Parys, K.A. 2019. Comparative activity of commercial baculovirus formulations against heliothine pests of cotton. Southwestern Entomologist. 44(1):105-115.

Interpretive Summary: New microbial insecticides developed from viral isolates of different species in the genus Helicoverpa have been recently introduced to the market and are receiving increased interest from growers. In this study, we compared new virus-based products to the first microbial insecticide labeled for lepidopteran control, Elcar, which was introduced over 40 years ago. We utilized two separate assay methods to evaluate mortality and pupation rates of bollworm and tobacco budworm larvae exposed to various doses of each microbial insecticide. When exposed to non-Bt cotton leaves sprayed with various microbial insecticides, there was no discernable differences among microbial treatments within insect species. Although it appears that the efficacy of newly-released formulations of viral-based products has not improved since it was originally released in 1975, the use of these products should be promoted given their low cost and the environmental benefits associated with reducing synthetic insecticide use.

Technical Abstract: Nuclear polyhedrosis viruses have been labeled for use as microbial insecticides in agronomically-important crops in the U.S. since the 1970s. New products developed from viral isolates of different species in the genus Helicoverpa (Heliothis) have been introduced to the market and are receiving renewed attention for controlling heliothine pests. Therefore, we evaluated comparative activities among the first NPV registered in the U.S. and two commercially-available baculovirus products for controlling bollworms and tobacco budworms using two separate laboratory assays. Based on formulated product comparison of LC50s from laboratory assays at 7d, Gemstar was 2.4 and 3.7 fold less fold less active than Elcar against bollworms and tobacco budworms, respectively. Heligen was 2.9 and 7.1 fold more active than Elcar against bollworm and tobacco budworm, respectively. However, once corrected for polyhedral occlusion body (POB) concentrations, there was no difference in bollworm susceptibility to any of the three products tested. Tobacco budworm was more susceptible to Heligen than Gemstar in laboratory overlay assays following correction for POB concentration differences, which may be due to the interrelatedness of this species with the old world bollworm. We failed to detect any discernable difference among the highest labeled rate of any formulated microbial insecticides sprayed on non-Bt cotton leaves regarding mortality of bollworms or tobacco budworms at 14 d and percent pupation at 20 d post-treatment. Although the activity of wild-type baculovirus has changed little over the past four decades, the use of these products should be encouraged whenever possible. The potential ecological benefits of preserving beneficial insects and reducing selection for insecticide resistance should be promoted as long as effectiveness and costs are reasonable.