Abstract
The daily susceptibility rhythm to permethrin and the expression level of the delta class glutathione S-transferase (BgGSTD1) gene were investigated in Blattella germanica. Male cockroaches were exposed to the same concentration of permethrin at different times in a light-dark cycle, and results showed that the highest resistance occurred at night. Furthermore, the circadian rhythmicity of permethrin susceptibility was demonstrated by the highest resistance at subjective night under constant darkness. The mRNA level of the BgGSTD1 gene in the fat body of B. germanica peaked early in the day or subjective day under light-dark or constant dark conditions, whereas enzyme activity of cytosolic GSTs did not reflect the rhythmic pattern as well as BgGSTD1 expression. RNA interference (RNAi) was employed to study the function of BgGSTD1 in the circadian rhythm of permethrin susceptibility in B. germanica. Both BgGSTD1 mRNA level and cytosolic GSTs activity were significantly decreased by dsGSTD1 injection. In addition, survival of B. germanica with silenced BgGSTD1 was significantly decreased at night but not in the day when the cockroaches were exposed to permethrin. Total cytosolic GSTs activity demonstrated that is not the only gene involved in the circadian regulation of the permethrin resistance, although it is one of the major regulators of permethrin resistance.
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