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LABORATORY EVALUATION OF SELECTED INSECTICIDES ON FIELD-COLLECTED POPULATIONS OF BOLLWORM AND TOBACCO BUDWORM LARVAE-2017-UPDATE

Abstract

During 2017, bollworm (CEW) and tobacco budworm (TBW) larvae and adults were collected from a variety of host crops and evaluated for their susceptibilities to MVP II®, cypermethrin, and spinosad (Tracer®). Results were compared to historical data collected throughout a twenty three-year study period which began in 1995. TBW, in Georgia, have remained susceptible to the effects of Cry1Ac, the Bt protein, found in MVPII®. However, MVPII® LC50s for CEW collected during the past two seasons have been some of the highest recorded. In 2016, MVPII® LC50s for CEW larvae ranged between 19.8-527 ppm, with a mean LC50 of 213 ppm. In 2017, MVPII® LC50s for CEW larvae ranged between 88.4-3941 ppm, with a mean LC50 of 1141 ppm (21-fold higher than MVPII® LC50s recorded during the mid-1990s and 116-fold higher as compared to a susceptible lab colony). Although cypermethrin remained an effective insecticide to control CEW, the 2017 values (ranging between 2.9-9.18 ppm) were among the highest values recorded since 2011. In general, the effectiveness of cypermethrin for the control of TBW larvae has declined. In 2017, the mean LC50 (~194 ppm) for cypermethrin against TBW larvae was 30-fold higher than the LC50s obtained during the mid-1990s and 94-fold higher as compared to a pyrethroid-susceptible lab population. Data obtained from adult vial tests confirmed the larval studies and further indicated that CEW and TBW populations in Georgia were becoming less susceptible to the effects of pyrethroid insecticides. Spinosad (Tracer®) has remained relatively effective against CEW and TBW throughout the study period. Prior to the 2017 season, the LC50s ranged between 0.30-3.92 ppm for CEW and between 0.14-0.84 ppm for TBW. CEW and TBW 2017 LC50s for spinosad (Tracer®) were comparable.

Acknowledgements

UWG Biology Department, Georgia Cotton Commission, Cotton Incorporated

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