Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/1996
Publication Date: N/A
Interpretive Summary: The horn fly is a dung-breeding, blood-sucking pest of cattle that causes economic losses in excess of $876 million annually in milk and meat production in the dairy and beef cattle industries. Insecticides are commonly used to manage the adult flies, but this practice has caused the pest to become resistant to many of the chemicals currently approved for use. As a result, some insecticides now target immature stages of horn flies in cattle dung. Unfortunately, insecticides in cattle dung may harm beneficial insects that develop in dung with horn flies. Some dung-inhabiting insects feed on immature stages of horn flies or make the dung pat unsuitable for fly development such as the dung- burying activity of dung beetles. Ivermectin is currently available to livestock producers for horn fly control and can be purchased as an injectable or pour-on formulation. Ivermectin, in both formulations, is excreted in cattle dung. This study evaluated the effects of the pour-on formulation of ivermectin on the horn fly and two species of beneficial insects associated with cattle dung. Dung, containing ivermectin, controlled the horn fly for up to 6 weeks; whereas, populations of two species of dung- burying beetles were reduced for 1-3 weeks. The results of this study suggest that ivermectin in the pour-on formulation can provide good control of horn flies and should not have a major adverse impact on dung-breeding beneficial insects.
Technical Abstract: Dung from two steers treated with the recommended therapeutic dose of a pour-on formulation of ivermectin was bioassayed with the horn fly Haematobia irritans (L.) and the introduced dung beetles Euoniticellus intermedius (Reiche) and Onthophagus gazella (F.). Emergence of adult horn flies reared on dung from the treated steers was significantly reduced for 5-6 wk when compared with emergence of flies reared on dung from an untreated steer. There were no effects on the mean numbers of brood balls produced by either dung beetle species. However, emergence of adult E. intermedius and O. gazella from brood balls made with dung from the treated steers was reduced for 1-2 wk and 2-3 wk, respectively.