Influence of permethrin, diazinon and ivermectin treatments on insecticideresistance in the horn fly (Diptera : Muscidae)

The history of insecticide resistance in the horn fly, Haematobia irritans, and the relationship between the characteristics of horn fly biology and i nsecticide use on resistance development is discussed. Colonies of suscepti ble horn flies were selected for resistance with six insecticide treatment regimens: continuous single use of permethrin, diazinon and ivermectin; per methrin-diazinon (1:2) mixture; and permethrin-diazinon and permethrin-iver mectin rotation (4-month cycle). Under laboratory conditions, resistance de veloped during generations 21, 31 and 30 to permethrin, diazinon and iverme ctin, respectively. The magnitude of resistance ranged from < 3-fold with i vermectin to 1470-fold with permethrin. Field studies demonstrated that use of a single class of insecticidal ear tag during the horn-fly season resul ted in product failure within 3-4 years for pyrethroids and organophosphate s, respectively. In laboratory studies, use of alternating insecticides or a mixture of insecticides delayed the onset of resistance For up to 12 gene rations and reduced the magnitude of pyrethroid resistance. In field studie s, yearly alternated use of pyrethroids and organophosphates did not slow o r reverse pyrethroid resistance (Barros et al., unpublished data), while a 2-year alternated use with organophosphates resulted in partial reversion o f pyrethroid resistance. When pyrethroid and organophosphate ear tags were used in a mosaic strategy at two different locations, efficacy of products did not change during a 3-year period. (C) 1998 Australian Society for Para sitology. Published by Elsevier Science Ltd. All rights reserved.