Population biology of the saw-toothed grain beetle, Oryzaephilus surinamensis (Coleoptera: Silvanidae), in an experimental model of a fabric treatment

Abstract

AbstractThe response of populations of the saw-toothed grain beetle, Oryzaephilus surinamensis (Linnaeus) (7022/1 strain), to insecticide treatments of different extent and standard concentration was studied over 16 weeks (no more than two generations) in experimental bins containing a wheat bulk and 16 kibbled wheat-filled refuges. Populations comprised initially low frequencies of resistant phenotypes, as would occur in natural populations where resistant alleles had newly arisen. The degree of control achieved was related to the extent of treatment. Distribution of adult beetles was greatly influenced by the effects of insecticide treatment superimposed on intrinsic microhabitat preferences. Live beetles were recovered from all bins, although numbers sampled from wheat bulks of treated bins were 1–6% of that of the untreated bin. More live beetles were sampled from wheat bulks than were recovered from all respective refuges, except in one treated bin. Live beetles were more numerous in refuges in corners and in those furthest from refuges on treated walls. Beetles were more likely to die in refuges in coiners and lower down in the bins or in refuges on treated walls adjacent to untreated walls. Although treatments produced heavy mortality, the frequencies of resistant individuals did not increase significantly. This could either be because treatments were equally successful in eliminating homozygous susceptible and heterozygous individuals, or because selection in favour of resistant individuals was too weak to be detectable, especially if there were negative correlations between viability and fecundity. Significant genetic structuring of refuge subpopulations with respect to the resistance phenotypes was noted and appeared to be related to behavioural preferences for microhabitat.