THE CURRENT STATUS OF INSECTICIDE RESISTANCE IN MUSCA-DOMESTICA IN ENGLAND AND WALES AND THE IMPLICATIONS FOR HOUSEFLY CONTROL IN INTENSIVEANIMAL UNITS

Following the 1984-85 housefly (Musca domestica L.) resistance survey, a similar survey was carried out between January 1990 and April 1992 in order to monitor changes in UK housefly resistance. Samples of fly populations were collected from 35 farms throughout England and Wales. Dose-response data were obtained by topical application and feeding t est methods. For both methods the knockdown (KD) after 48 h was used f or all the dose-response comparisons. The ranges of resistance factors for the topical application method were for methomyl, 1.6-20.0 at KD5 0 and 4.5-34.4 at KD95; for azamethiphos, 2.5-58.5 at KD50 and 5.0-260 4 at KD95; for pyrethrins+piperonyl butoxide, 1.2-9.6 at KD50 and 1.6- 14.7 at KD95; and for permethrin, 2.2-118.8 at KD50 and 4.3-200.0 at K D95. The ranges of the resistance factors for the feeding tests were f or methomyl, 1.2-56.1 at KD50 and 3.1-80.0 at KD95, and for azamethiph os, 3.9-125.0 at KD50 and 4.4-380.0 at KD95. The means of resistance f actors for all of the insecticides showed increases over those obtaine d in a previous survey carried out in 1984-85. The significance of the results for housefly control in intensive animal units in the UK is d iscussed.