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 heliothine genera Helicoverpa, Heliothis, and Chloridea have been introduced to the market and are receiving renewed attention for controlling heliothine pests. Two laboratory assays were used to evaluate comparative activities among the first nuclear polyhedrosis viruses registered in the U.S. and two commercially-available baculovirus products for controlling bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Chloridea virescens (F.). Based on comparisons of LC50s of formulated products from laboratory overlay assays at 7 days, Gemstar was 2.4 and 3.7 fold less active than Elcar against bollworm and tobacco budworm, respectively. Heligen was 2.9 and 7.1 fold more active than Elcar against bollworm and tobacco budworm, respectively. However, once corrected for concentration of polyhedral occlusion bodies, susceptibility of bollworm did not differ to any of the three products tested. Tobacco budworms were more susceptible to Heligen than Gemstar in laboratory overlay assays following correction for differences in concentration of polyhedral occlusion bodies, which might be caused by interrelatedness of the species with the Old World bollworm. No discernable difference in death of bollworms or tobacco budworms was detected among the greatest labeled rate of any formulated microbial insecticide sprayed on leaves of non-Bt cotton (Gossypium hirsutum L.) at 14 days and percentage of pupation at 20 days post-treatment. Although the activity of wild-type baculovirus has changed little during the past four decades, use of the products should be encouraged whenever possible. Potential ecological benefits of preserving beneficial insects and reducing selection for resistance to insecticides should be promoted as long as effectiveness and costs are reasonable.
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Vol. 44 • No. 1