Autodissemination of a beet armyworm (Lepidoptera: Noctuidae) baculovirus under laboratory conditions

Basic aspects of autodissemination of SeMNPV for suppression of Spodoptera exigua (Hubner) were investigated. Talc was the most effective carrier among 6 viral formulations tested. The corrected mean viral-induced mortality for progeny from mating pairs in which only the male was surface-contaminated with viral talc dust was 24.2%. The higher transmission efficiency produced using talc may be attributable to its better adhesion. Egg chorion consumed by a hatching larva averaged 5.7% of the egg surface area. Combined with known dose-mortality value, we estimated that 18 occlusion bodies per egg were required to obtain LD80 for hatching larvae. Scanning electron microscopy revealed that most treated eggs had some observable polyhedra on the chorion. Polyhedra were concentrated on the upper hemisphere of the eggs and along the ridged surfaces of the chorion, particularly at the rosette where they would most likely be ingested during eclosion. SeMNPV produced significantly higher mortality among F-1 progeny from mating pairs with both partners contaminated than from mating pairs with single partners contaminated. Male-contaminated parents were almost as effective in transovum transmission as female-contaminated parents. In serial matings, SeMNPV induced mortality in progeny up to the 4th mating. SeMNPV induced much higher mortality via horizontal transmission among cohorts when hatched larvae from the same egg mass were reared together.