Abstract
Fitness costs associated with resistance to insecticides have been well documented, usually at normal temperature conditions, in many insect species. In this study, using chlorpyrifos-resistant homozygote (RR) and chlorpyrifos-susceptible homozygote (SS) of resistance ace1 allele of Plutella xylostella (DBM), we confirmed firstly that high temperature experience in pupal stage influenced phenotype of wing venation in insecticide-resistant and insecticide-susceptible Plutella xylostella, and SS DBM showed significantly higher thermal tolerance and lower damages of wing veins under heat stress than RR DBM. As compared to SS DBM, RR DBM displayed significantly lower AChE sensitivity to chlorpyrifos, higher basal GSTs activity and P450 production at 25°C, but higher inhibitions on the enzyme activities and P450 production as well as reduced resistance to chlorpyrifos under heat stress. Furthermore, RR DBM displayed significantly higher basal expressions of hsp69s, hsp72s, hsp20,hsp90,Apaf-1, and caspase-7 at 25°C, but lower induced expressions of hsps and higher induced expressions of Apaf-1,caspase-9, and caspase-7 under heat stress. These results suggest that fitness costs of chlorpyrifos resistance in DBM may partly attribute to excess consumption of energy caused by over production of detoxification enzymes and hsps when the proteins are less demanded at conducive environments but reduced expressions when they are highly demanded by the insects to combat environmental stresses, or to excess expressions of apoptotic genes under heat stress, which results in higher apoptosis. The evolutionary and ecological implications of these findings at global warming are discussed.
Highlights
Resistance is a benefit to pests when they are treated with the agrochemicals, it is known that this resistance may come at a cost of other life-history traits
The activities of the four resistancerelated enzymes were inhibited in all heat treatments in both susceptible homozygote (SS) and RR, but the inhibitions were significantly higher in RR than individual with SS genotype (in SS) (Fig. 2)
Total nine hsp70s, one hsc70, hsp90, and hsp20 were identified from DBM in China, and previous studies indicated that Hsp70 proteins were encoded by a multigene family in some other insect species, such as Drosophila melanogaster (Mou et al 2011) and Anopheles albimanus (Benedict et al 1993)
Summary
Resistance is a benefit to pests when they are treated with the agrochemicals, it is known that this resistance may come at a cost of other life-history traits. This fitness cost associated with resistance to agrochemicals has been well documented in many species (Bourguet et al 2004; Berticat et al 2008) and is believed to be the main constraint for the quick emergence of agrochemical resistance in agro-ecosystems. Perturbed physiological functions caused by excess production of detoxifying enzymes are thought to be partially responsible for fitness costs (Higginson et al 2005; Konopka et al 2012)
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