FENVALERATE PENETRATION, METABOLISM, AND EXCRETION IN PYRETHROID-SUSCEPTIBLE AND RESISTANT HELIOTHIS-VIRESCENS (LEPIDOPTERA, NOCTUIDAE)

Fenvalerate was significantly less toxic to Heliothis virescens (F.) (PEG 87 strain) third instars than to pyrethroid-susceptible BCIRL-S strain third instars; the resistance ratio estimated from LD90s at 48 h was 79.2. Studies with fenvalerate-C-14 revealed that the toxicity differential had a pharmacokinetic component consisting of slower penetration and faster metabolism of the pyrethroid in PEG 87 larvae as compared with BCIRL-S larvae. Enhanced excretion of fenvalerate equivalents in PEG 87 larvae was of minor importance. However, the interstrain difference in fenvalerate pharmacokinetics was not sufficient to account fully for the difference in toxicity. Nerve insensitivity, which previously has been shown to be present in PEG 87 larvae, most likely was involved.