In 1952 the Egyptian Ministry of Health regarded the Egyptian house fly, Musca domestica vicina, as developing such serious resistance to the chlorinated hydrocarbon insecticides that they recommended the discontinuance of such materials for general house fly control. A study was made to determine the resistance of house flies from localities where insecticides had been used for several years but where no treatment had been undertaken for at least one fly season. Flies from 11 localities in or near Cairo were tested with topical applications of acetone solutions of DDT, lindane, pyrethrins, and parathion. From the LD-50's computed from 24-hour mortalities, none of the strains tested showed a high degree of resistance.
Six weekly applications of BHC dust containing 1.3 per cent of gamma isomer to breeding places in one village where a similar treatment had previously been effective did not control the flies, and by the seventh week after the initial treatment resistance had increased at least threefold. These results indicate that with the cessation of treatments with chlorinated hydrocarbon insecticides Egyptian house flies lose resistance, but that resistance rapidly increases with reapplications of these materials. It is therefore recommended that other types of insecticide or techniques be employed to control this serious pest.
On assignment from the United States Department of Agriculture, Agricultural Research Service, Entomology Research Branch.