Toxicological studies using DDT and trichlorphon on the house fly Musca domestica L. : A dissertation submitted in partial fulfilment of the requirement for the Degree of Bachelor of Agricultural Science with Honours in the University of Canterbury

Abstract

The preliminary aim was to investigate the possible variation in susceptibility of different body regions, of an insect, to topical applications of DDT. The house fly Musca domestica L. was chosen as the test insect because it is easily reared in the laboratory and has a short, 2 week life cycle. This allowed maximum experimentation to be carried out in the time available. Two strains of the house fl.y were used. One: a DDT susceptible strain (DDT 'S') obtained from Mrs. Foot of the Plant Diseases Division of the D.S.I.R.* at Auckland. The other: a resistant strain (DDT 'R') that had been bred here at Lincoln College for several years, although originally also obtained from the D.S.I.R. in Auckland. The two body regions chosen for topical application were the dorsal pronotum and the ventral abdomen. Fisher (1952) pointed out that mortality differences could be obtained with equal doses of p' DDT applied at different sites on the house fly body. Keiser et al. (1971) showed that one of the greatest differences occurred between the dorsal thorax and abdominal midventer, when working with DDT on Oriental fruit flies and Melon flies. The second part of the experiment was to establish the possibility of a difference in response between the DDT 's' and DDT 'R' strains when trichlorphon was applied to the ventral abdomen. It is known that the main method of house fly resistance to DDT is through the presence of the enzyme DDT dehydrochlorinase in the DDT 'R' flies, and that this enzyme acts by dehydrochlorinating the pp' DDT, converting it into inactive DDB (Sternberg et al .1950). Trichlorphon, itself an active dipteran insecticide, if dehydrochlorinated, is converted into dichlorvos, a much more active insecticidal compound. Thus, if the mechanisms of DDT and trichlorphon dehydrochlorination were simiilar it would be expected that the DDT 'R" strain would be more susceptible than the DDT 's' strain to trichchlorphon due to the further activation to dichlorvos of the trichlorphon in the DDT 'R' strain.