Mortality of horn fly larvae (Diptera : Muscidae) in bovine dung supplemented with ergotamine and N-formyl loline

Dung-dwelling larvae of ectoparasites of livestock such as the horn fly, He matobia irritans (L.), may be exposed to greater than or equal to 1 differe nt alkaloid species in dung from animals ingesting herbage of the tall fesc ue (Festuca arundinacea Schreb.)-endophyte association (Neotyphodium coenop hialum (Morgan-Jones & W. Game) Glenn, Bacon & Hanlin comb. nov.). First-in star horn flies were exposed to bovine dung supplemented with up to 50 mu M each of N-formyl loline and ergotamine tartrate in factorial combination. In the absence of ergotamine tartrate, N-formyl loline caused a linear decl ine in the number of pupae recovered, and probit analysis indicated an LC50 of 36 mu M In the absence of N-formyl loline, significant quadratic respon ses of larvae to ergotamine tartrate were established, and probit analysis indicated a LC50 of 34 mu M. An interaction (P < 0.001) was found between t he 2 alkaloids for larval survival. This interaction showed that ergotamine tartrate moderated the toxicity of N-formyl loline and indicates that a me mbrane-bound receptor may be involved. There was no evidence of carryover o f effects of alkaloids on subsequent stages of development or expressed as abnormalities of pupae or adults. Interactions between alkaloids probably a re involved in ether plant-herbivore relationships of endophyte-infected gr asses.