Evaluation of Current Tarnished Plant Bug (Hemiptera: Miridae) Thresholds in Transgenic MON 88702 Cotton Expressing the Bt Cry51Aa2.834_16 Trait

Abstract

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is an important pest of cotton in many areas of the southern United States. An experiment was conducted at two locations in Mississippi during 2016 and 2017 to evaluate action thresholds for tarnished plant bug on a novel Bacillus thuringiensis cotton that expresses the Cry51Aa2.834_16 toxin. Treatments included the current action threshold, a 2× threshold, and treatments where insecticides were only applied during the early season (preflower) or only during late season (during flowering) based on the current action thresholds. These were compared to an untreated control and a weekly insecticide use regime that received weekly insecticide sprays. All treatments were imposed on both Bt Cry1Aa2.834_16 cotton and a nontraited cotton. The Bt Cry1Aa2.834_16 trait reduced the number of tarnished plant bugs and injury, and improved yields compared to nontraited cotton. For all spray treatments except the weekly insecticide use regime, yields were greater for the Bt Cry51Aa2.834_16 cotton than the nontraited cotton. In terms of thresholds, Bt Cry1Aa2.834_16 cotton sprayed based on current action thresholds resulted in similar yields to the weekly insecticide use regime of both cotton types. In contrast, the 2× threshold resulted in lower yields than the current threshold for both cotton types. Though thresholds intermediate to the currently recommended action threshold and the 2× threshold were not tested, these data suggest that currently recommended action thresholds appear appropriate for Bt Cry51Aa2.834_16 cotton. These results suggest that this trait will be an important component of current IPM programs in cotton where tarnished plant bug is an important pest.

Biology, Ecology, and Pest Management of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois) in Southern Row Crops

“…The lack of an effective pheromone has severely limited the utility of ecological studies evaluating the movement of Lygus in the landscape and future research should focus on this aspect of their biology. Transgenic cotton varieties expressing insecticidal proteins have reduced the number of pesticide applications required for control of L. lineolaris in Thryvon cotton (Cry51Aa2.834_16) compared to non-Thryvon cotton [ 161 , 162 ]. Bt cotton expressing these Cry proteins need to be tested further to establish their action thresholds for Lygus management before releasing them to cotton growers for large scale cultivation.…”

“…Initial studies with transformed plants expressing the TIC807 protein reported 35% to 78% mortality of newly eclosed L. hesperus nymphs in the laboratory [ 160 ], but no such studies have been published on L. lineolaris . Field experiments have shown a reduction in the number of sprays needed for L. lineolaris management in Thryvon cotton compared to non-Thryvon cotton [ 161 , 162 ]. Graham and Stewart [ 161 ] observed a reduction of 1.25 insecticide sprays for L. lineolaris in Thryvon cotton compared to a near isogenic non-Thryvon cotton variety when sprays were made based on the current action threshold.…”

“…Additionally, yields of Thryvon cotton were greater than non-Thryvon cotton when neither variety was sprayed for L. lineolaris throughout the year [ 161 ]. A similar study was conducted to compare a 2× threshold to the current threshold and to compare early season benefits to late season benefits [ 162 ]. In that study, fewer small (1st–2nd instar) and large (5th instar) nymphs were observed on unsprayed Thryvon cotton than unsprayed non-Thryvon cotton.…”

“…No differences were observed for medium (3rd instar) nymphs. At the current action threshold (see the Mississippi Insect Control Guide for Agronomic Crops), 1.5 fewer sprays were needed in Thryvon cotton compared to non-Thryvon cotton [ 162 ]. This is similar to the 1.25 reduction in the number of applications observed by Graham and Stewart [ 161 ], and Thryvon technology is expected to reduce foliar insecticide applications by one to two applications per year.…”

“…Yields of unsprayed Thryvon cotton were about double that of unsprayed, non-Thryvon cotton. Additionally, yields of Thryvon cotton were greater than non-Thryvon cotton for all spray regime treatments (threshold, 2× threshold, early season only, and late season only), except for the weekly spray treatment [ 162 ]. Moreover, yields of Thryvon cotton in the threshold, 2× threshold, and late season only spray regimes were greater than yields in Thryvon cotton that was not sprayed for L. lineolaris .…”