Dietary Effects of Methoprene on Lymantria dispar (Lepidoptera: Lymantriidae) Growth and Nuclear Polyhedrosis Virus Yield

Abstract

Gypsy moth, Lymantria dispar L., larvae were treated with the juvenile hormone mimic, methoprene, to determine the effect on yield and virulence of a multi embedded nuclear polyhedrosis virus (LdMNPV) produced in vivo. Methoprene was applied to diet surfaces 15 days after egg hatch and larvae were infected with virus on either day 15, 17, 20, or 25 to pertnit a progressive increase in larval biomass. Larvae were harvested 10 d after virus inoculation and polyhedra were extracted. Methoprene alone prolonged larval development, prevented pupation, and increased mean maximum larval weight by 52% compared with untreated control insects. Larvae treated simultaneously with methoprene and virus weighed significantly less than uninfected larvae treated with methoprene, suggesting that LdMNPV inhibited the response of insects to the morphogenetic effects of methoprene. Larval weight increased and polyhedra production per milligram of tissue decreased on methoprene-treated diets with progressive delay in virus inoculation. Despite a 45% increase in body weight, larvae treated with methoprene and inoculated with virus on day 25 produced the lowest polyhedral occlusion body (OB) yield per milligram of tissue and per insect. Maximum virus yield was achieved from infecting larvae treated with methoprene with LdMNPV on day 17 or 20. These treatments yielded 19% more progeny OBs than the virus alone treatment. Bioassays showed no change in virulence of virus derived from larvae reared on diet treated with methoprene. These results indicate that methoprene can be used as a diet adjuvant for increasing gross production of LdMNPV in vivo.