Topical treatment of calves with synthetic pyrethroids: effects on the non-target dung fly Neomyia cornicina (Diptera : Muscidae)

Dung from calves treated with synthetic pyrethroids negatively influenced, in varying degrees, survival, reproduction and size of the common dung fly Neomyia cornicina (Fabricius). This was documented in assays where the copr ophagous larvae and adults of N. cornicina were exposed to dung collected f rom calves dosed with topical preparations of deltamethrin, flumethrin, cyf luthrin, and alpha -cypermethrin. Larval mortality was significantly increa sed in dung collected up to at least seven days after treatment with deltam ethrin, alpha -cypermethrin and cyfluthrin. Alpha-cypermethrin caused signi ficant mortality of adults allowed to feed on moist dung. Nulliparous flies fed for six days on dung collected three days after treatment of calves wi th alpha -cypermethrin or deltamethrin showed little or no ovarian developm ent. A tendency for a comparable effect with flumethrin was also observed. A connection between ovarian development and inhibition of feeding was indi cated by the observation of significantly lowered excretion rates in flies exposed to residues of deltamethrin, alpha -cypermethrin and flumethrin. La rvae that survived exposure to dung from calves dosed with deltamethrin, al pha -cypermethrin, or cyfluthrin gave rise to smaller flies. The effect on adult fly size decreased when larvae were exposed to dung collected at long er times after treatment of the calves. Adult fly size was significantly re duced in dung collected up to 14 days (alpha -cypermethrin) or up to 28 day s after treatment (deltamethrin and cyfluthrin). Fluctuating asymmetry of a wing vein character did not reflect the anticipated levels of exposure. Th e study strongly indicated that the use of synthetic pyrethroids affected t he insect dung fauna and that such use may reduce dung decomposition.