Methoprene-nucleopolyhedrosis virus interactions in Hyphantria cunea (Drury).

Supernumerary moults of Hyphantria cunea were induced by incorporating methoprene (Altosid?) in a wheat germ diet. Based on calculated LD50 values, methoprene concentrations of 1, 10, 100 ppm had no adverse effect on the development of nucleopolyhedrosis in preinfected H. cunea larvae. Last-instar lar vae prefed on methoprene-treated diet remained susceptible to a subsequent challenge of a nonoccluded nucleopolyhedrosis virus preparation. Extended prefeeding (14 days) on methoprene diet caused a reduction in percent virus-induced larval mortality and an increase in the LT50 value. Polyhedra, isolated from viral-infected methoprene-treated larvae, were infectious when fed back to other 5th-instar larvae. The potential increased use of insect growth regulators (IGR's) and patho gens for insect control will increase the likelihood of their interfacing with one another under field conditions. Of particular concern is what effect IGR's might have on pathogens acting as natural mortality factors on non target insect species. Presently, little information is available on the inter action of IGR's and natural control agents such as insect pathogens. In this study, the IGR, methoprene (Altosid?), which induces supernumerary moults among lepidopterous larvae having variable numbers of instars (Sehnal, 1976), and a nucleopolyhedrosis virus (NPV), genus Baculovirus, which infects the fall webworm, Hyphantria cunea (Drury), were selected for this study. Objectives related to methoprene-NPV interactions in H. cunea were to determine: 1) what dietary concentrations would methoprene induce supernumerary moults; 2) if methoprene interfered with the NPV infection process; and 3) if exposure to methoprene-treated diet changed larval susceptibility to viral infection.