Monitoring for resistance to cypermethrin in budworm (H. Virescens) and bollworm (H. Zea) and to malathion in boll weevil in the brazos river bottom, Texas
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Vial bioassays were conducted during 1999 with adults of budworm, bollworm and boll weevil. Field collected moths were tested for resistance to cypermethrin and boll weevils for resistance to malathion. The frequency and level of resistance to cypermethrin continues to be very high in budworm and the frequency of this resistance is increasing in bollworm. The vial assay was used to monitor for resistance to malathion in boll weevil populations in Burleson County, TX. Differences in boll weevil susceptibility to malathion depending on weevil age or origin (traps or cotton squares) and bioassay temperature were determined. The susceptible strain of boll weevils obtained from the USDA-ARS in Stoneville, Mississippi, was used as an internal control. Mortality caused by malathion was found to be lower in 2-3 day-old weevils emerging from squares when compared with older weevils collected from squares and trapped weevils of unknown age. Altogether, these data suggest that the frequency of pyrethroid use against bollworm should decrease. The increase in tolerance to malathion in boll weevils observed in the laboratory indicates that monitoring for resistance should continue, with special attention to young weevils emerging from squares. These findings need to be confirmed with malathion field efficacy studies.
