Mortality of horn fly (Diptera: Muscidae) larvae in bovine during supplemented with loline alkaloids from tall fescue

Larvae of arthropod ectoparasites of livestock, such as the horn fly, Haematobia irritans (L.), may be exposed to acyl-loline alkaloids in dung of ruminant livestock ingesting herbage of the tall fescue (Festuca arundinacea Schreb.)-endophyte association [Neotyphodium coenophialum (Morgan-Jones & W. Gams) Glenn, Bacon & Hanlin comb. nov.]. Biological activity of alkaloid-supplemented bovine dung was assayed by growth, development, and survival of 1st instars of horn fly. An extract from tall fescue seed, containing N-formyl loline (NFL), N-acetyl loline (NAL), and loline (59:21:20 by mass, respectively) caused 100% mortality of horn fly larvae when dung was supplemented at greater than or equal to 100 mu g/g. Probit analysis of data corrected for natural mortality indicated a LD50 of 30 mu g/g (95% fidicial limits: 20-49 mu g/g). When horn fly larvae were introduced to dung supplemented with up to 50 mu M of acyl-loline derivatives, mortality of larvae varied significantly between alkaloids (P < 0.0001). Probit analysis indicated that NFL [LD50:34 mu M (95% fidicial limits: 3-53 mu M)] was more toxic than NAL [LD50: 46 mu M (0-83 mu M)], and that loline hydrochloride was not toxic.