Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 1998
Publication Date: N/A
Interpretive Summary: Horn flies are serious pests of cattle in the United States causing over 850 million dollars in damage annually. In addition, resistance to available chemical pesticides is a growing problem and development of new control technology is needed. A potential target for the development of new control technology is to interfere with nutritional requirements for growth and development of horn fly larvae. Horn fly larval growth and development occurs in cattle dung which contains large populations of bacteria and fungi. These microorganisms interfere with research on the nutritional physiology and toxicology of horn fly larvae by interacting and altering test substances added to the dung making interpretation of results difficult. New research has demonstrated that bacteria and fungi in cattle dung can be controlled by addition of a combination of antibacterial and antifungal agents without affecting the growth and development of horn fly larvae. This finding facilitates interpretation of nutritional and toxicological studies conducted with horn fly larvae which will aid in the development of new control technology.
There is no chemically defined diet available for larval horn flies, Haematobia irritans (L.). Microbial effects on test supplements added to bovine feces must be reduced or controlled; however, effective antifungal agents have not been previously identified. This study tested toxicity of the antifungal agents amphotericin B, clotrimazole, griseofulvin, haloprogin, miconazole, nystatin, and tolnaftate to larval horn flies, eac of which appeared to be potentially useful in bovine fecal medium. The toxicity of ethanol, methanol, dimethylsulfoxide (DMSO) and dimethylformamide (DMF) were also evaluated. DMSO and DMF were incompatible with horn fly larvae at the tested concentrations. Methanol and ethanol were each tolerated to about 2% (vol/wt), but exhibited increasing toxic effects at higher concentrations. Ethanol supplementation up to 2% had a positive effect on larval growth and survival. A combination of streptomycin, nystatin and ethanol were found to be compatible with use in horn fly larval bioassays.