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A range of insecticides were tested on a resistant strain of bed-bugs (Cimex lectularius L.) from Israel. Resistance was restricted to organophosphorus compounds. Only some of the phosphorothioate compounds were involved, but there was no simple indication of the resistance mechanism on basis of structure of the compounds.Nine malathion analogues were tested on the bed-bugs, and relative levels of resistance to them compared with insect strains specifically resistant to malathion. Distinct differences in the bed-bug spectrum suggested that a carboxyesterase was not solely responsible for resistance. This was further supported by the ineffectiveness of triphenylphosphate against malathion-resistance in the bugs.The F1 progeny from reciprocal mass crosses were tested with malathion. Their response, in both cases, resembled the susceptible type, indicating a recessive autosomal character, a result unique in organophosphorus-resistance. Tests on F2 and backcrosses indicated that a single gene was responsible. Results using fenchlorphos were quite similar and probably the same gene (and mechanism) is involved.

Tissue distribution, elimination, and metabolism of intraperitoneally administered photoheptachlor was studied in male rabbits. Biological half-life of the compound at 0.8 mg/kg dose level was about 70 days. The radioactivity was excreted almost exclusively in urine. Analyses of the urine extracts revealed that all the radioactivity was in the form of four metabolites, none of which corresponded to the parent compound. Gas chromatography-mass spectrometry analysis of one of the metabolites indicates that this metabolite arises by oxidative dechlorination of photoheptachlor and is eliminated both in free and conjugated form. Tissue distribution indicated that maximal amounts of the radiocarbon were present in visceral fat and the residues declined with the passage of time.The observation that cyclodiene insecticides undergo isomerization (Rosen et al., 1966) has resulted in numerous reports which show that these photoconversions are fairly common and take place not only under laboratory conditions but also in simulated and natural environments

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