Methoprene for control of horn flies: a suppression program on the Island of Molokai, Hawaii.

In an island-wide program, we evaluated methoprene in the drinking water of cattle to suppress a population of Haemalobia irritans (L.) preparatory to the release of sterile males. The treatment resulted in an avg 83% suppression of horn flies and a range of 80–99.8% suppression in various treatment areas. A maximum 92% suppression (avg of 24 flies/animal) was observed when insecticide treatments were applied at locations where methoprene treatments were difficult to maintain. The results indicate that methoprene can be used effectively in a large-scale suppression program; however, the water treatment technique is most efficient and effective for large herds where there is strict control of water sources. In situations with only one or 2 animals or alternate sources of water, use of conventional insecticides appears more effective. Additionally, the study indicates the importance of treating on an area-wide basis; untreated herds in an area undoubtedly reduce the benefits of control measures.