interactions between entomopathogenic fungus, metarhizium anisopliae and sublethal doses of spinosad for control of house fly, musca domestica

background: metarhizium anisopliae strain iran 437c is one of the most virulent fungal isolates against house fly, musca domestica . the objective of this study was to determine the interaction of this isolate with sublethal doses of spino­sad against housefly. methods: in adult bioassay, conidia of entomopathogenic fungus were applied as inoculated bait at 10 5 and 10 7 spore per gram and spinosad at 0.5, 1 and 1.5 µg (a.i.) per gram bait. in larval bioassay, conidia were applied as combina­tion of spore with larval bedding at 10 6 and 10 8 spore per gram and spinosad at sublethals of 0.002, 0.004 and 0.006 µg (ai) per gram medium. results: adult mortality was 48% and 72% for fungus alone but ranged from 66–87% and 89–95% in combination treat­ments of 10 5 and 10 7 spore/g with sublethal doses of spinosad respectively. the interaction between 10 5 spore/g with sublethals exhibited synergistic effect, but in combination of 10 7 spore in spite of higher mortality, the interac­tion was additive. there was significant difference in lt 50 among various treatments. lt 50 values in all combination treat­ments were smaller than lt 50 values in alone ones. larval mortality was 36% and 69% for fungus alone but ranged from 58%–78% and 81%–100% in combination treatments of 10 6 and 10 8 spore/g medium with sublethals of spino­sad respectively. the interaction was synergistic in all combination treatments of larvae. conclusion: the interaction between m. anispliae and spinosad indicated a synergetic effect that increased the house fly mortality as well as reduced the lethal time.