Behavioral Responses of Thrips (Thysanoptera: Thripidae) and Tarnished Plant Bug (Hemiptera: Miridae) to a New Bt Toxin, Cry51Aa2.834_16 in Cotton.

Thrips (Thysanoptera: Thripidae) and tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), are among the most important insect pests of cotton, Gosssypium hirsutum, in the mid-southern United States. These pests are currently managed primarily by insecticides; however, a new Bt toxin, Cry51Aa2.834_16 is under evaluation for control of thrips and tarnished plant bug. Experiments were conducted to evaluate the behavioral response of thrips and tarnished plant bug to Bt Cry51Aa2.834_16. Adult thrips avoided Bt Cry51Aa2.834_16 cotton in field choice tests and in separate field tests of Bt and non-Bt cotton not treated with insecticides. In a greenhouse choice test, approximately twice as many adult thrips and eggs were found on non-Bt compared with Bt Cry51Aa2.834_16 cotton. Similarly, in a field test of nontreated Bt Cry51Aa2.834_16 and non-Bt cotton, 68% of adult thrips collected were found on non-Bt cotton. In cotton that was not sprayed with insecticides, Bt Cry51Aa2.834_16 did not affect the distribution of tarnished plant bug within the canopy, although more square and flower injury was caused by tarnished plant bug in non-Bt cotton. Adult tarnished plant bug exhibited a nonpreference for diet containing lyophilized Bt Cry51Aa2.834_16 leaves and for excised Bt Cry51Aa2.834_16 squares in choice tests with non-Bt squares. The behavioral responses of these pests when exposed to this new Bt toxin will play a key role in the efficacy and potential resistance management strategies if this new technology is incorporated in an overall cotton insect pest management system.

Monitoring Seasonal Distribution of Thrips Vectors of Soybean Vein Necrosis Virus in Alabama Soybeans.

Soybean vein necrosis virus (SVNV), a new virus in the genus Orthotospovirus, has been found in all soybean-growing regions in the United States and Ontario, Canada. Soybean thrips, Neohydatothrips variabilis (Beach) (Thysanoptera: Thripidae), tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), and eastern flower thrips, Frankliniella tritici (Fitch) (Thysanoptera: Thripidae) are reported vectors of this virus, but there are no reports on their distribution in Alabama. A monitoring study was conducted in 2015 and 2016 to determine thrips species composition and abundance in Alabama soybean agroecosystems. Thrips were monitored weekly by collecting them on yellow sticky traps and soybean plant parts including foliage and reproductive structures. All three reported vectors of SVNV were identified in Alabama, with N. variabilis and F. tritici as the predominant species, while F. fusca was not consistently collected from soybean plants. Four additional thrips species were collected, of which Echinothrips americanus (Morgan) (Thysanoptera: Thripidae) was commonly found on soybean at all three locations. Results presented in this study provide new information about seasonal thrips species abundance in soybean agroecosystems in Alabama, and is an important first step to understanding thrips vector species of epidemiological importance in the Southern United States.

Insecticide Resistance Signals Negative Consequences of Widespread Neonicotinoid Use on Multiple Field Crops in the U.S. Cotton Belt.

The intensification of industrial agriculture has been enabled by improved crop varieties, genetically engineered crops, fertilizers, and pesticides. Over the past 15 years, neonicotinoid seed treatments have been adopted worldwide and are used on a large proportion of U.S. field crops. Although neonicotinoids are used widely, little is known about how large-scale deployment affects pest populations over long periods. Here, we report a positive relationship between the deployment of neonicotinoid seed-dressings on multiple crops and the emergence of insecticide resistance in tobacco thrips (Frankliniella fusca), a polyphagous insect herbivore that is an important pest of seedling cotton but not soybean or maize. Using a geospatial approach, we studied the relationship between neonicotinoid resistance measured in 301 F. fusca populations to landscape-scale crop production patterns across nine states in the southeastern U.S. cotton production region, in which soybean, maize and cotton are the dominant crops. Our research linked the spatiotemporal abundance of cotton and soybean production to neonicotinoid resistance in F. fusca that is leading to a dramatic increase in insecticide use in cotton. Results demonstrate that cross-crop resistance selection has important effects on pests and, in turn, drives pesticide use and increases environmental impacts associated with their use.

Thrips Settling, Oviposition and IYSV Distribution on Onion Foliage.

Thrips tabaci Lindeman (Thysanoptera: Thripidae) adult and larval settling and oviposition on onion (Allium cepa L.) foliage were investigated in relation to leaf position and leaf length at prebulb plant growth stages under controlled conditions. In the laboratory, four and six adult females of T. tabaci were released on onion plants at three-leaf stage and six- to eight-leaf stage, respectively, and thrips egg, nymph, and adult count data were collected on each of the three inner most leaves at every 2-cm leaf segment. Thrips settling and oviposition parameters were quantified during the light period on the above ground portion of onion plants from the distal end of the bulb or leaf sheath "neck" through the tips of the foliage. Results from studies confirmed that distribution of thrips adults, nymphs, and eggs were skewed toward the base of the plant. The settling distributions of thrips adults and nymphs differed slightly from the egg distribution in that oviposition occurred all the way to the tip of the leaf while adults and nymphs were typically not observed near the tip. In a field study, the foliage was divided into three equal partitions, i.e., top, middle, basal thirds, and thrips adults by species, primarily Frankliniella fusca (Hinds) and T. tabaci, were collected from each partition to determine if there was a similar bias of all adult thrips toward the base of the plant. The results suggested that adults of different species appear to segregate along leaf length. Finally, thrips oviposition on 2-cm segments and Iris yellow spot virus positive leaf segments were quantified in the field, irrespective of thrips species. Both variables demonstrated a very similar pattern of bias toward the base of the plant and were significantly correlated.