Autodissemination of a Baculovirus for Management of Tobacco Budworms (Lepidoptera: Noctuidae) on Tobacco

An autodissemination technique for control of the tobacco bud worm, Heliothis Virescens (F.), was tested for 2 yr in tobacco fields in Kentucky and North Carolina. We used pheromone-baited traps to attract male moths into contamination stations, where they were forced to crawl through a powder formulation of a baculovirus, Autographa californica nuclear polyhedrosis virus (AcNPV). After they were contaminated with Ac- NPV powder, males escaped back to the field. When males mated with wild females, they transferred some of the AcNPV powder to females, which in turn surface-contaminated their eggs. When larvae chewed through the egg chorion, some of them ingested enough viral polyhedra to become lethally infected. Tests of this autodissemination technique in the field required measurements of contamination rates of males, eggs, and larvae. Because a reliable method for sampling adult females of H. Virescens is not available, their contamination rate could not be directly assessed. Pheromone-baited monitoring traps showed that 0-30% of the males were marked with a fluorescent marking powder, which was used in the AcNPV formulation. Examination by scanning electron microscopy showed that an average of 6.7-7.8% of the eggs collected from AcNPV-treated fields had polyhedra clustered on the upper hemisphere near the micropyle. Light microscope examination showed that an average of 0.7-11.9% of larvae reared from eggs collected in AcNPV-treated fields died from the virus. AcNPV-induced larval mortality peaked at ≈25% at the Kentucky location in 1989. Although the autodissemination technique functioned, it was not economically effective because the AcNPV transmission and subsequent larval mortality were limited. In part, this may have been because the dispersal area of Heliothis moths was large relative to the small experimental plot size and the short distance between fields, resulting in migration of moths and dilution of AcNPV-induced mortality.