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BACKGROUND Insecticide resistance arises at a given location in response to selection acting on novel genotypes or standing variation, or allelic migration. Fitness costs of resistance may slow resistance evolution or result in reversion to susceptibility, but consistent and geographically widespread use of insecticides may provide sufficient selection to offset the fitness costs of resistance. Understanding this relationship is important to the success of insecticide resistance management. We report the existence of fitness costs of neonicotinoid resistance in field‐collected populations of the tobacco thrips (Frankliniella fusca), which increasingly challenge upland cotton production in the southeastern USA. RESULTS: Populations (14 of 15 in 2015; 4 of 5 in 2016) investigated showed a loss of resistance to imidacloprid after multiple generations without exposure to the insecticide. Populations studied in 2016 were each split into two colonies, and one of each pair was repeatedly exposed to imidacloprid. In three of the four populations that lost resistance, imidacloprid‐exposed colonies lost resistance significantly more slowly than did corresponding unexposed colonies. CONCLUSION: For imidacloprid resistance to be broadly increasing in the landscapes of the southeastern USA despite fitness costs of resistance, selection for resistance must be sufficient to overcome the costs. Findings encourage investigation into why costs are overcome in this system, potentially including geographic extent of neonicotinoid use or prevalence of low‐dose exposure. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) is an early-season cotton pest. Seedlings are injured by larvae, which hatch from eggs oviposited into seedlings and feed on developing plant tissue. Better understanding F. fusca oviposition in cotton may improve their management and address new challenges such as resistance to neonicotinoid seed treatments (NSTs). Cotton seedlings exposed to F. fusca were either cleared and stained to determine egg density and location, or dissected and washed to determine larval distribution. Experiments were conducted in the greenhouse with a susceptible population and field with a NST-resistant population. Eggs of both populations were recovered predominantly in cotyledons. Larvae were more uniformly distributed on seedlings. On NST seedlings, oviposition by the susceptible population was reduced and preference shifted to true leaves. NSTs did not alter egg placement by the resistant population. These findings suggest that injury to cotton seedlings is primarily caused by F. fusca emerging on the cotyledons, and then moving to developing leaves. The oviposition shift in NST plants correlates with how systemic NSTs have been reported to concentrate in cotyledons. This can better inform management tactics in cotton, such as well-timed foliar sprays, which, given the current resistance issue, are needed to maintain effective thrips management. [ABSTRACT FROM AUTHOR]

Neonicotinoids are a popular and widely-used class of insecticides whose heavy usage rates and purported negative impacts on bees and other beneficial insects has led to questions about their mobility and accumulation in the environment. Neonicotinoid compounds are currently registered for over 140 different crop uses in the United States, with commercial growers continuing to rely heavily on neonicotinoid insecticides for the control of key insect pests through a combination of in-ground and foliar applications. In 2008, the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) began testing for neonicotinoids in groundwater test wells in the state, reporting detections of one or more neonicotinoids in dozens of shallow groundwater test wells. In 2011, similar detection levels were confirmed in several high-capacity overhead center-pivot irrigation systems in central Wisconsin. The current study was initiated to investigate the spatial extent and magnitude of neonicotinoid contamination in groundwater in and around areas of irrigated commercial agriculture in central Wisconsin. From 2013–2015 a total of 317 samples were collected from 91 unique high-capacity irrigation wells and tested for the presence of thiamethoxam (TMX), a neonicotinoid, using enzyme-linked immunosorbent assays. 67% of all samples were positive for TMX at a concentration above the analytical limit of quantification (0.05 μg/L) and 78% of all wells tested positive at least once. Mean detection was 0.28 μg/L, with a maximum detection of 1.67 μg/L. Five wells had at least one detection exceeding 1.00 μg/L. Furthermore, an analysis of the spatial structure of these well detects suggests that contamination profiles vary across the landscape, with differences in mean detection levels observed from landscape (25 km), to farm (5 km), to individual well (500 m) scales. We also provide an update of DATCP’s neonicotinoid monitoring in Wisconsin’s shallow groundwater test wells and private potable wells for the years 2011–2017. [ABSTRACT FROM AUTHOR]

BACKGROUND: Reports of neonicotinoid seed treatment (NST) failure against Frankliniella fusca in the mid‐south and southeastern USA led to the discovery of widespread resistance in these insect populations. Previous studies of NSTs in other crops have shown the concentration of the insecticide to change over time, which could reduce its efficacy. To understand this temporal effect in cotton with F. fusca, our study examined how plant age alters the effects of NSTs (imidacloprid, imidacloprid + thiodicarb and thiamethoxam) by examining larval establishment at multiple seedling ages during the period of cotton seedling susceptibility to this insect. Additionally, we used F. fusca populations with differing neonicotinoid sensitivity levels to understand how resistance impacts this changing efficacy. RESULTS: Greenhouse studies showed that larval numbers were significantly greater on older NST‐grown cotton seedlings. The population with elevated neonicotinoid resistance had a more rapid increase in larval number on thiamethoxam‐treated plants over time. CONCLUSION: NSTs reduce the number of F. fusca larvae on younger seedlings, but this effect declines as seedlings age. The duration of efficacy is shorter against neonicotinoid‐resistant populations. Neonicotinoid resistance in cotton‐infesting F. fusca populations may be accelerated by this time‐dependent decrease in efficacy, which likely encourages low‐dose exposure to these insecticides. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Detection of neonicotinoid resistance in populations of tobacco thrips, Frankliniella fusca Hinds, throughout the southeastern USA has motivated an examination of alternative insecticides to control problematic infestations on seedling cotton. The objective of this study was to refine understanding of stage-specific mortality and reduced oviposition of several common insecticides (acephate, abamectin, cyantraniliprole, spinetoram, imidacloprid, imidacloprid+thiodicarb, thiamethoxam) on neonicotinoid resistant and susceptible F. fusca populations under laboratory and field conditions. RESULTS Laboratory studies revealed that the average number of eggs per female and larval or adult survivorship responses differed by insecticide and were dependent on the resistance status of the population . In the presence of neonicotinoids, the resistant F. fusca populations exhibited lower mortality and higher egg counts than the susceptible population. In the field study, similar patterns of oviposition suppression were observed, indicating that some insecticides may impact reproductive rate. CONCLUSION This study shows that insecticides have different effects on F. fusca oviposition events, larval and adult mortality that are dependent on neonicotinoid resistance status. Because insecticides tested in this study have varied activity on specific F. fusca life stages (e.g. oviposition suppression, larvicidal activity, adulticidal activity), knowledge of stage-specific activity can be used to improve control and enhance long-term product stewardship. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Over the past two decades, neonicotinoid seed treatments have become the primary method to manage tobacco thrips, Frankliniella fusca Hinds, on seedling cotton. Because this insect is highly polyphagous and the window of insecticide exposure is short, neonicotinoid resistance was expected to pose a minimal risk. However, reports of higher than expected F. fusca seedling damage in seed-treated cotton fields throughout the Mid-South and Southeast US production regions suggested neonicotinoid resistance had developed. To document this change, F. fusca populations from 86 different locations in the eastern United States were assayed in 2014 and 2015 for imidacloprid and thiamethoxam resistance to determine the extent of the issue in the region. RESULTS Approximately 57 and 65% of the F. fusca populations surveyed had reduced imidacloprid and thiamethoxam sensitivity respectively. Survivorship in diagnostic bioassays was significantly different at both the state and regional scales. Multiple-dose bioassays conducted on 37 of the populations documented up to 55- and 39-fold resistance ratios for imidacloprid and thiamethoxam respectively. CONCLUSION Estimates of neonicotinoid resistance indicate an emerging issue for management of F. fusca in the eastern United States. Significant variation in survivorship within states and regions indicated that finer-scale surveys were needed to determine factors (genetic, insecticide use) driving resistance evolution. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Select populations of Colorado potato beetle, Leptinotarsa decemlineata, in Wisconsin have recently become resistant to soil-applied neonicotinoids in potato. Sublethal insecticide concentrations persisting in foliage through the growing season may select for resistance over successive years of use. Over the 2 years of this study, the aim was to document the in-plant insecticide concentrations over time that result from four different types of soil-applied insecticide delivery for thiamethoxam and imidacloprid in potato, and to measure the impact upon L. decemlineata populations following treatments. After plant emergence, insect life stages were counted and plant tissue was assayed weekly for nine consecutive weeks using ELISA. RESULTS Peak concentration of both imidacloprid and thiamethoxam occurred in the first sample week following plant emergence. The average concentration of both insecticides dissipated sharply over time as the plant canopy expanded 50 days after planting in all delivery treatments. Both insecticides were detected at low levels during the later weeks of the study. Among-plant concentrations of both neonicotinoids were highly variable throughout the season. Populations of L. decemlineata continued to develop and reproduce throughout the period of declining insecticide concentrations. CONCLUSION Sublethal, chronic exposure to soil-applied systemic insecticides resulting from these delivery methods may accelerate selection for resistant insects in potato. © 2014 Society of Chemical Industry [ABSTRACT FROM AUTHOR]