Enhanced pyrethroid hydrolysis in pyrethroid-resistant larvae of the tobacco budworm, Heliothis virescens (F.)

Abstract

Larvae of Heliothis virescens (F.) collected from the field in the Imperial Valley of California were reared in the laboratory and selected periodically with flucythrinate. At the end of the selection experiment, this Imperial Valley (IV) strain had LD 50 values that were ca. 68, 53, 16, 23, and 2 times higher for flucythrinate, fenvalerate, DDT, carbaryl, and ethyl parathion, than a susceptible American Cyanamid laboratory strain (ACCO). This IV strain was then transferred to LSU, without further selection pressure, where it was found to be ca. 12.2-, 5.4-, and 2.5-fold less susceptible to trans-permethrin, cis-permethrin, and fenvalerate, respectively, when compared with another laboratory strain (LSU lab). Piperonyl butoxide did not synergize trans-permethrin in the IV strain. Conversely, profenofos increased the toxicity of trans-permethrin to levels nearly identical to that for the LSU lab strain. The rates of hydrolysis were ca. 2- to 3-fold higher in the IV strain than in the LSU lab strain for all three pyrethroids. Isoelectric focusing also indicated higher levels of trans-permethrin hydrolytic activity in the IV strain as opposed to the LSU lab strain as well as the presence of an additional peak of activity. These observations suggest that there is both a qualitative and a quantitative difference in the ability of the pyrethroid-resistant IV strain to hydrolyze pyrethroids.