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.