Comparative expression of two detoxification genes by Callosobruchus maculatus in response to dichlorvos and Lippia adoensis essential oil treatments

The cowpea beetle, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae), is a field-to-store pest, which can cause up to 80% damage of cowpea grains within 3months of storage. The control approach consisting of application of synthetic pesticides has become challenging following the increased resistance and toxicity to non-target organisms and the environment. Here, we hypothesized that Lippia adoensis essential oil (EO) (plant-based insecticide) can repress cytochrome P450-dependent mono-oxygenase and glutathione-S-transferase (GST) genes and suppress C. maculatus resistance to dichlorvos (O,O-dimethyl-O-2,2-dichlorovinylphosphate or DDVP). The methods consisted of separately exposing C. maculatus adults to cowpea seeds treated with DDVP and L. adoensis EO. Their physiological and molecular responses were monitored for five generations. Adult mortality of DDVP-treated beetles significantly decreased across generations and negatively correlated with the reproduction parameters (increase in fecundity and adult emergence) and seed damage. Similarly, the decrease in adult susceptibility corresponded with the increase in the expression levels of cytochrome P450 and GST genes (overexpression of genes). However, the adult susceptibility to EO treatments remained consistent across generations and correlated with the down-regulation of targeted genes from the third generation (F-3). These results support our hypotheses and provide a probable molecular basis of resistance to DDVP and susceptibility to L. adoensis EO in C. maculatus. Therefore, L. adoensis EO represents an alternative insecticide that could be employed to enhance the vulnerability of this pest.