DEFINING RESISTANCE TO PYRETHROIDS BY LARVAE OF TOBACCO BUDWORM WITH VIAL BIOASSAY IN TEXAS

摘要

The vial test (VT) for larvae of the tobacco budworm, Heliothis virescens (F.) (TBW), is superior to that for adults. Few LC50s of cypermethrin were determined for field collected larvae from TX. Most LC50s for larvae were determined for a selected resistant strain (PEG87), but this strain is not representative of responses to cypermethrin by those collected from cotton fields across TX. LC50s by VT of a susceptible strain of larvae by tralomethrin, lambda cyhalothrin, bifenthrin, cyfluthrin, cypermethrin, fenvalerate and permethrin ranged from a low of 0.025 to a high of 0.51 mg/vial, respectively, a 20 fold difference. Neonate larvae from one field in the Brazos Valley (BV) showed 10.3% (pretreatment), 25.6%, 19.5%, 44.5% and 26.6% resistance fromfield collected eggs 1-3 d following four applications of cypermethrin based on a discriminating dose of LC81. Neonates did not show high levels of resistance. Average levels of resistance to cypermethrin were 37.0%, 63.5%, 72.0% and 89.0% from 31 Julyto 20 August for first through the fifth instar larvae collected from cotton in the BV. Field collected larval populations increased in resistance as the season progressed.