EFFECTS OF RESIDUES OF DELTAMETHRIN IN CATTLE FECES ON THE DEVELOPMENT AND SURVIVAL OF 3 SPECIES OF DUNG-BREEDING INSECT

Objective To assess the toxicity to insects of drug residues excreted in cattle faeces following treatment with deltamethrin. Design Bioassa ys were performed on one species of dung-breeding fly (Musca vetustiss ima) and two species of dung beetle (Onthophagus binodis and Euonitice llus fulvus). Animals Cattle on properties near Kangaroo Valley, Canbe rra and Gundagai were treated with pour-on formulations of deltamethri n. Untreated animals acted as controls. Procedures Faeces from treated and untreated cattle were inoculated with newly emerged fly larvae or fed to adults of two species of dung beetle. Percentage survival and duration of development provided measures of the toxicity of deltameth rin residues in faeces. Results Residues of deltamethrin were excreted in concentrations sufficient to inhibit survival of larvae of M vetus tissima for 1 to 2 weeks after treatment. Peak concentrations of 0.4mg deltamethrin/kg dry weight of faeces occurred 3 days after treatment and were sufficient to kill adult beetles for at least twice this peri od. With one of two formulations tested, there was evidence of a reduc tion in dung beetle fecundity and an increase in the duration of juven ile development. A model of the effect of deltamethrin on the breeding success of dung beetles in the field suggests that a single treatment , applied when most of the population is in a non-parous condition, ma y cause up to 75% reduction in beetle activity by the end of the seaso n. Multiple treatments at 10 or 21 day intervals may drive local popul ations towards extinction. Conclusion Depending on the time and freque ncy of treatment, the effect of deltamethrin on insects in cattle faec es may range from negligible to catastrophic.