Selection for and against resistance to insecticides in the absence of insecticide: a case study of malathion resistance in the saw-toothed grain beetle,Oryzaephilus surinamensis(Coleoptera: Silvanidae)

Abstract

In the absence of insecticide there may be intense selection against alleles conferring insecticide resistance, so that these alleles will decline in frequency. On the other hand, selection will act to favour alleles at modifier loci which cause resistance alleles to become coadapted and increase in fitness even in the absence of insecticide. The relative effectiveness of these two processes is of practical importance and theoretical interest. The fate of polymorphism for malathion resistance was studied in the saw-toothed grain beetle, Oryzaephilus surinamensis (Linnaeus). Five to six lines of each of four strains (8401, 8401sel, 8518B and L1040), each polymorphic for resistance phenotypes, were maintained in insecticide-free culture for up to nine generations, over which period the response of individuals to a discriminating dose of 65 mg irr 2 malathion was determined. There was significant reversion to susceptibility in the related strains 8401, 8401sel and 8518B. Assuming resistance to be primarily controlled by a single major locus, resistant homozygote and heterozygote fitnesses in the absence of insecticide were estimated to be 0.92, 0.83 and 0.68, respectively. The initial frequency of the resistant allele was inversely related to the time since last exposure to insecticide, and also to the fitness of the resistant allele. This could be explained by the selection of modifier alleles that reduce the fitness cost of resistance in the absence of insecticide. In strain L1040 the proportion of resistant individuals actually increased over time (after the second generation) in the absence of insecticide. The fitness of the susceptible allele in this case was 0.83. In all strains there was significant variation among lines in relative fitness and initial resistance allele frequency. Analysis of knockdown proportions revealed highly significant variation between generations that is not easily interpreted in genetic terms but is better explained by limitations of the knockdown bioassay.

Use of Mathematical Models to Estimate Characteristics of Pyrethroid Resistance in Tobacco Budworm and Bollworm (Lepidoptera: Noctuidae) Field Populations

“…Restricted relative Þtness estimates in the absence of selection pressure were 0.79 for the resistant homozygote and 0.89 for the heterozygote and were statistically different from zero and unity at the 5% signiÞcance level. These estimates were similar to relative Þtness estimates reported for the saw-toothed grain beetle, Oryzaephilu surinamensis (L.) (Coleoptera: Silvanidae), in the absence of malathion selection pressure (Muggleton 1986, Mason 1998. Muggleton (1986) reported relative Þtness estimates for resistant homozygotes and heterozygotes of 0.82 for both genotypes, assuming resistance was conferred by one dominant allele at one locus.…”

“…Muggleton (1986) reported relative Þtness estimates for resistant homozygotes and heterozygotes of 0.82 for both genotypes, assuming resistance was conferred by one dominant allele at one locus. Mason (1998) reported relative Þtness estimates of 0.92, 0.83, and 0.68 for both genotypes in three experiments under the same assumption. Finally, environmental effects on Þtness in May and June were statistically different from unity at the 5% signiÞcance level in the unrestricted and restricted models, suggesting that tobacco budworms may have been less able to survive the vial test bioassay at the beginning relative to the end of the growing season.…”

Variation in Resistance to Pyrethroids in <I>Helicoverpa armigera</I> From Benin Republic, West Africa

“…Based on antagonistic selective pressures principle that insecticide selection favors resistant individuals and resistance Þtness cost disadvantages them in the absence of insecticides and in accordance with Georghiou et al (1983), Mallet (1989), Bonning and Hemingway (1991), Hemingway et al (1992), Rodriguez et al (1993), Tabashnik (1994), Guillemaud et al (1998), Mason (1998), and Lenormand and Raymond (1998), several strategies can be used in resistance management: 1) Temporal (window strategy) or spatial (mosaic strategy) rotation involves alternation of insecticide selection and no-selection periods. Nevertheless, insecticide rotation efÞciency can encounter the problem of modiÞer gene selection that reduces resistance Þtness costs (Mason 1998).…”

Analogous pleiotropic effects of insecticide resistance genotypes in peach–potato aphids and houseflies

“…However, despite the extensive literature on the subject, there are relatively few empirical studies that confirm that investment in such adaptations exacts a cost (Minkoff and Wilson, 1992;Carriere et al, 1994Carriere et al, , 1995Yamamoto et al, 1995;Chevillon et al, 1997;Alyokhin and Ferro, 1999;Boivin et al, 2001). Some authors have failed to reveal any detrimental effects of insecticide resistance (Follett et al, 1993;Tang et al, 1997Tang et al, , 1999Baker et al, 1998) and some have shown such organisms to be even more successful than their susceptible counterparts in the absence of insecticides (Omer et al, 1992;Bloch and Wool, 1994;White and Bell, 1995;Mason, 1998;Haubruge and Arnaud, 2001). In other studies, some measures of fitness have been negatively affected, others positively (Brewer and Trumble, 1991) and different strains of insect, exhibiting resistance to the same compound, can show opposite associations (Chevillon et al, 1997;Hollingsworth et al, 1997;Oppert et al, 2000).…”