Abstract
Glucose-aversion is a heritable trait that evolved in a number of German cockroach (Blattella germanica L.) populations in response to strong selection with glucose-containing insecticide baits. However, in the absence of glucose-containing bait, glucose-averse (GA) cockroaches have lower performance than wild-type (WT) cockroaches in several fitness-determining traits. We allocated 48 caged populations initiated with homozygous GA and WT adults to four dietary treatments consisting of either pure rodent chow, rodent chow mixed to yield a content of either 20% glucose or 20% fructose, or a treatment consisting of choice between the 20% glucose- and the 20% fructose-containing food. After 6 months we found significantly higher frequency of WT individuals in populations restricted to the 20% glucose food, and after 12 months all dietary treatments contained significantly more WT individuals than expected. In accompanying experiments, we found lower survival and longer development time of GA nymphs restricted to glucose-containing food. We furthermore found evidence for assortative mating of females with males from their own genotype, with significant differences within WT cockroaches. Our study shows experimental evidence that within heterogeneous populations, WT German cockroaches will over time prevail in abundance over GA individuals, even when glucose is not a dietary component.
Highlights
Efficacious for targeted control[26]
Foods containing glucose above a very low detection limit are rejected by GA cockroaches, protecting them from ingesting the insecticide contained in the bait[28,30]
Development time was significantly longer in GA nymphs that developed on a standard laboratory diet with glucose content below their detection limit[40], this was not the case for nymphs developing on artificial glucose-free diets[41]
Summary
Efficacious for targeted control[26]. many populations have independently evolved physiological resistance mechanisms against the insecticides in baits and some have evolved behavioural mechanisms as well[27,28,29,30,31,32,33,34,35]. In response to persistent anthropogenic selection with glucose-containing baits, populations of the German cockroach have evolved a strong aversion to glucose[28,30]. Foods containing glucose above a very low detection limit are rejected by GA cockroaches, protecting them from ingesting the insecticide contained in the bait[28,30]. Several studies indicate lower fitness of GA than WT cockroaches in the absence of insecticide, which predicts a relative increase in WT frequency over time as an evolutionary response even in the absence of glucose. We compared nymphal survival and development time as well as male mating success and female fecundity between homozygous GA and WT cockroaches to explore possible mechanisms that underlie the evolutionary responses in the experimental populations
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