Do metabolic detoxification enzymes mediate pyrethroid resistance in the southern chinch bug?

Metabolic detoxification is an extremely important biochemical mechanism used by insects to survive xenobiotics produced both by plants (e.g., allelochemicals) and humans (e.g., insecticides). Types of pyrethroids detoxification reaction include oxidation, hydrolysis, and/or conjugation of pyrethroids catalyzed by endogenous enzymes, such as cytochrome P450-dependent monooxygenases (P450s), esterases, and glutathione-S-transferases (GSTs). The southern chinch bug, Blissus insularis Barber, is notorious for severely damaging St. Augustinegrass and rapidly developing insecticide resistance. Since the 1950s, this insect pest has developed resistance to multiple insecticide classes, including the pyrethroids. We hypothesized that the documented insecticide resistance is conferred by enhanced metabolic enzyme activities in this insect pest. To investigate potential biochemical mechanisms, different geographic populations of southern chinch bugs were collected in Florida and assessed for their susceptibility to a commonly used pyrethroid (bifenthrin) by a contact bioassay. Using single chinch bug homogenates, we conducted micro-assays to measure common metabolic enzyme activities (P450s, esterases, and GSTs) in both females and males using model substrates. Results showed gender- and bifenthrin susceptibility-related differences in the metabolic enzyme activities. We also conducted esterase Native PAGE assays to confirm micro-assay results suggesting involvement of hydrolytic enzymes in bifenthrin resistance.