Dieldrin and Diazinon Resistance in Populations of the Australian Sheep Blowfly, Lucilia cuprina, from Sheep-grazing Areas and Rubbish Tips

Abstract

Populations of L. cuprina collected from adjacent sheep-grazing areas and rubbish tips in Victoria (Mansfield and Warrnambool) and New South Wales (Lismore) were tested for resistance to the insecticides diazinon and dieldrin. Populations from sheep-grazing areas had a significantly higher diazinon Rop-l allele frequency than those from adjacent tips with the Victorian populations being more resistant than those from Lismore. Victorian sheep and tip populations had similar gene frequencies at the dieldrin resistance locus, but the Rdl allele frequency was significantly greater in the population at the tip than in the population from the sheep-grazing area at Lismore. The Rdl allele is at a higher frequency in flies from the Lismore area than in Victorian populations. The results at both loci are explained by a balance of selection and gene flow between sheep and tip populations and by selective differences between geographical areas.The exceptionally high frequency of the dieldrin Rdl allele in populations at the Lismore tip may be partially explained by the use of dichlorvos for fly control. Dosage mortality curve and genetic analyses suggest that dichlorvos (an organophosphorus compound) may select at the dieldrin resistance locus. Possible mechanisms for this are discussed.The consequences of genetic differentiation between L. cuprina populations within a region for an autocidal control program are considered.Extra keyword: microdifferentiation.

Frequency-dependent selection at the diazinon resistance locus of the Australian sheep blowfly, Lucilia cuprina

“…It should be noted that the present results do not provide an explanation for the recessiveness of resistance, with respect to viability, observed in egg implant studies on sheep over a considerable concentration range 1984). Irrespective of the facilitation of SS, the RS genotype was significantly more viable in the presence of diazinon.…”

“…However, recent studies in L. cuprina have shown specific fitness differences may occur at concentrations that are sub-lethal for each genotype 1984) questioning both the tenet of fixed fitness sets and the assumption that fitness is determined only by concentration thresholds about which mortality is genotypically dependent (Brown and Pal, 1971). That is, they suggest that the evolution of insecticide resistance may involve soft, rather than hard, selective processes in some circumstances .…”

“…In sheep-grazing areas of Australia susceptible flies are currently rare Hughes, 1981;McKenzie, 1984). Selection for insecticide resistance is concentrated at the larval stage of the life cycle (Whitten et a!., 1980).…”

Diazinon resistance in Lucilia cuprina; mapping of a fitness modifier

“…Therefore, in the case of dieldrin resistance a new chemical was substituted for blowfly control soon after resistance evolved so that resistant homozygotes never constituted more than 20 per cent of the population (Hughes and McKenzie, 1986). Continued use of diazinon after resistance evolved to that insecticide reaching near fixation in some populations McKenzie, 1984). If the general genetical arguments on the conditions necessary for the selection of fitness modifiers (Fisher, 1958;Charlesworth, 1979) are extended to studies on resistance it is apparent that such modifiers can only be at a selective advantage in the presence of the resistance allele.…”

Genetic Architecture and Adaptation: Quantitative Analysis of Sheep and Refuse Tip Populations of the Australian Sheep Blowfly, Lucilia cuprina

“…cuprina may be collected over a considerable geographic range, in proximity to sheep and in adjacent refuse tips (Waterhouse and Paramo nov 1950;Norris 1959;Kitching 1974). While tip populations are often seen as transient there is some evidence that this may not be the case (Foster et al 1975;Rice 1986) particularly as insecticide-resistant genotypes indicate differentiation between adjacent populations as an outcome of a balance between selection and limited gene flow (McKenzie 1983(McKenzie , 1984. This study attempts to elucidate this model of population structure within the framework discussed above.…”