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 d ung of ruminant livestock ingesting herbage of the tall fescue (Festuc a arundinacea Schreb.)-endophyte association [Neotyphodium coenophialu m (Morgan-Jones & W. Gams) Glenn, Bacon & Hanlin comb. nov.]. Biologic al activity of alkaloid-supplemented bovine dung was assayed by growth , development, and survival of 1st instars of horn fly. An extract fro m tall fescue seed, containing N-formyl loline (NFL), N-acetyl loline (NAL), and loline (59:21:20 by mass, respectively) caused 100% mortali ty of horn fly larvae when dung was supplemented at greater than or eq ual to 100 mu g/g. Probit analysis of data corrected for natural morta lity 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 signif icantly between alkaloids (P < 0.0001). Probit analysis indicated that NFL [LD50:34 mu M (95% fidicial limits: 3-53 mu M)] was more toxic th an NAL [LD50: 46 mu M (0-83 mu M)], and that loline hydrochloride was not toxic.