Fred R. Musser

Cold winter temperatures govern the distribution and abundance of many insect species, but refugia that provide microclimates can moderate temperature-driven mortality. Winter temperatures have been implicated in limiting the survival and range of Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae; redbanded stink bug), an economically damaging invasive pest in the southeastern United States, but the role of refugia in overwintering survival of this pest is poorly understood. We conducted 2 studies in successive years to evaluate how leaf litter from hardwoods, pines, and soybeans modulate overwintering site selection and survival of P. guildinii. In the second-year study, we also quantified the buffering effect of the 3 leaf litter types compared to ambient conditions and assessed diapause. In the first-year study, we found that stink bugs preferentially dispersed into leaf litter compared with remaining unsheltered on bare soil; no clear preference among leaf litter types was found. In the second year, however, no clear differences were found among leaf litter types and bare soil. Means of daily minimum temperatures under leaf litter were at least 3.0 ± 0.9 °C (SE) warmer and generally less variable than ambient conditions. While high mortality in both studies illustrates that more work must be done to fully understand overwintering survival, limited survival through potentially lethal conditions in the first-year study nonetheless emphasizes the possibility of populations persisting and rebounding in the following spring. Furthermore, our study highlights the potential for stink bugs to persist in areas with lethal ambient temperatures by dispersing into widely available substrates.

Diamide insecticides, such as chlorantraniliprole, have been widely used to control insect pests by targeting the insect ryanodine receptor (RyR). Due to the efficacious insecticidal activity of diamides, as well as an increasing number of resistance cases, the molecular structure of RyR has been studied in many economically important insects. However, no research has been conducted on diamide resistance and RyR in the soybean looper, Chrysodeixis includens, a significant crop pest. In this study, we found moderate resistance to chlorantraniliprole in a field population from Puerto Rico and sequenced the full‐length cDNA of the C. includens RyR gene, which encodes a 5124 amino acid‐long protein. Genomic analysis revealed that the CincRyR gene consists of 113 exons, one of the largest exon numbers reported for RyR. Alternative splicing sites were detected in the cytosolic region. The protein sequence showed high similarity to other noctuid RyRs. Conserved structural features included the selectivity filter motif critical for ryanodine binding and ion conduction, as well as various domains involved in ion transport. Two mutation sites associated with diamide resistance in other insects were screened but not found in the Puerto Rico field populations or in the susceptible lab strain. Gene expression analysis indicated high expression of RyR in the third instar larval stage, particularly in muscle‐containing tissues. Furthermore, exposure to a sublethal dose of chlorantraniliprole reduced RyR expression levels after 96 h. This study provides a molecular basis for understanding RyR structure and sheds light on potential mechanisms of diamide resistance in C. includens.

The noctuid moth soybean looper (SBL), Chrysodeixis includens (Walker) is an economically important pest of soybeans (Glycine max (L.) Merr.) in the southeastern United States. It has characteristics that are of particular concern for pest mitigation that include a broad host range, the capacity for annual long-distance flight, and resistance in some populations to important pesticides such as pyrethroids and chitin synthesis inhibitor. The biology of SBL in the United States resembles that of the fellow noctuid fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), a major pest of corn and several other crops. FAW exhibits a population structure in that it can be divided into two groups (host strains) that differ in their host preferences but are broadly sympatric and exhibit incomplete reproductive isolation. In this paper, strategies used to characterize the FAW strains were applied to SBL to assess the likelihood of population structure in the United States. Evidence is presented for two SBL strains that were defined phylogenetically and display differences in the proportions of a small set of genetic markers. The populations exhibit evidence of reproductive barriers sufficient to allow persistent asymmetry in the distribution of mitochondrial haplotypes. The identified molecular markers will facilitate studies characterizing the behaviors of these two populations, with relevance to pest mitigation and efforts to prevent further dispersal of the resistance traits.

The Noctuid moth soybean looper (SBL), Chrysodeixis includens (Walker), is an economically important pest of soybean (Glycine max (Linnaeus) Merrill). Because it is not known to survive freezing winters, permanent populations in the United States are believed to be limited to the southern regions of Texas and Florida, yet its geographical range of infestations annually extend to Canada. This indicates annual migrations of thousands of kilometers during the spring and summer growing season. This behavior is like that of the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), also a Noctuid that is a major global pest of corn. SBL and FAW are projected to have very similar distributions of permanent populations in North America based on climate suitability modeling and the overlap in the distribution of their preferred host plants (corn and soybean). It therefore seems likely that the two species will display similar migratory behavior in the United States. This was tested by identifying genetic markers in SBL analogous to those successfully used to delineate FAW migratory pathways and comparing the distribution patterns of the markers from the two species. Contrary to expectations, the results indicate substantial differences in migratory behavior that appear to be related to differences in the timing of corn and soybean plantings. These findings underscore the importance of agricultural practices in influencing pest migration patterns, in particular the timing of host availability relative to mean seasonal air transport patterns.

Spotted cucumber beetle, Diabrotica undecimpunctata (Coleoptera: Chrysomelidae), a North American native leaf beetle species also known as southern corn rootworm (SCRW), is a polyphagous pest of various crops including cucurbits (Cucurbitaceae), corn (Zea mays), soybeans (Glycine max), snap beans (Phaseolus vulgaris), peanut (Arachis hypogaea), and sweetpotato (Ipomoea batatas). Larvae are below-ground pests of corn, sorghum (Sorghum spp.), peanut, and sweetpotato. Adult damage impacts cucurbits by damage to seedlings and fruit and transmission of bacterial wilt (causal agent Erwinia tracheiphila) by eastern populations. Adult feeding also damages fresh market beans and occasionally leafy and fruiting vegetables. Damage on many other crops such as field soybeans, dry beans, and sorghum, is often cosmetic and/or inconsequential. Adults overwinter in mild climates and spread seasonally northward, with multiple generations and populations increasing into the late summer. Diverse natural enemies attack all stages, but their ecology and impact are poorly known, particularly below ground. A female-produced sex pheromone and floral volatiles are known attractants, and cucurbitacins (bitter phytochemicals) are feeding stimulants, offering potential selective behavioral control. Management practices are directed against pest complexes, including other below- and above-ground pests, depending on the crop. Chemical controls are soil-applied for protection from root-feeding larvae, systemic seed treatments for early-state crop feeding, and broadcast application in fruiting cucurbits and beans. Action thresholds and monitoring are not well developed. Cultural controls include field and cultivar choice, row covers in high-value crops, and available crop resistance. The wide host range, abundance, and mobility of adults make prediction and monitoring challenging.

Foliar-applied insecticide treatments may be necessary to manage thrips in cotton (Gossypium hirsutum L.) under severe infestations or when at-planting insecticide seed treatments do not provide satisfactory protection. The most common foliar-applied insecticide is acephate. Field observations in Tennessee suggest that the performance of acephate has declined. Thus, the first objective was to perform leaf-dip bioassays to assess if tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), in cotton production regions have evolved resistance to foliar-applied insecticides. A second objective was to assess the performance of commonly applied foliar insecticides for managing thrips in standardized field trials in Arkansas, Tennessee, Mississippi, and Texas. For both objectives, several insecticides were evaluated including acephate, dicrotophos, dimethoate, lambda-cyhalothrin, imidacloprid, and spinetoram. Field trials and bioassays were completed from 2018 to 2021. Dose-response bioassays with acephate were performed on tobacco thrips field populations and a susceptible laboratory population. Bioassay results suggest that tobacco thrips have developed resistance to acephate and other organophosphate insecticides; however, this resistance seems to be most severe in Arkansas, Tennessee, and the Delta region of Mississippi. Resistance to other classes of insecticides were perhaps even more evident in these bioassays. The performance of these insecticides in field trials was variable, with tobacco thrips only showing consistent signs of resistance to lambda-cyhalothrin. However, it is evident that many populations of tobacco thrips are resistant to multiple classes of insecticides. Further research is needed to determine heritability and resistance mechanism(s).

Overwintering success is an important determinant of arthropod populations that must be considered as climate change continues to influence the spatiotemporal population dynamics of agricultural pests. Using a long-term monitoring database and biologically relevant overwintering zones, we modeled the annual and seasonal population dynamics of a common pest, Helicoverpa zea (Boddie), based on three overwintering suitability zones throughout North America using four decades of soil temperatures: the southern range (able to persist through winter), transitional zone (uncertain overwintering survivorship), and northern limits (unable to survive winter). Our model indicates H. zea population dynamics are hierarchically structured with continental-level effects that are partitioned into three geographic zones. Seasonal populations were initially detected in the southern range, where they experienced multiple large population peaks. All three zones experienced a final peak between late July (southern range) and mid-August to mid-September (transitional zone and northern limits). The southern range expanded by 3% since 1981 and is projected to increase by twofold by 2099 but the areas of other zones are expected to decrease in the future. These changes suggest larger populations may persist at higher latitudes in the future due to reduced low-temperature lethal events during winter. Because H. zea is a highly migratory pest, predicting when populations accumulate in one region can inform synchronous or lagged population development in other regions. We show the value of combining long-term datasets, remotely sensed data, and laboratory findings to inform forecasting of insect pests.

Neonicotinoids have been implicated as a contributing factor to the observed decreases in honey bee populations. It has been suggested that honey bees can be exposed to seed-treated neonicotinoids through pollen and nectar from treated plants. To investigate the uptake and persistence of neonicotinoids in plant tissue and soil, we conducted seed treatment trials with corn, cotton, and soybean planted in Mississippi, Arkansas, and Tennessee during the 2013 and 2014 growing seasons. Leaf tissue was collected and analyzed beginning shortly after emergence until plants began to flower to better understand how neonicotinoid concentrations change in plant tissues over time. The youngest leaf in the terminal of the plant was sampled as an indicator of the neonicotinoid concentrations within the plant. Soil samples were also collected and analyzed for neonicotinoid concentrations at the first and last sampling dates. The mean clothianidin concentrations in corn treated with Poncho^® 250, 500, and 1250 seed treatments declined by 99.3, 99.3, and 97.8 percent, respectively, as the plants developed from seedlings to reproductive plants. The mean concentration of imidacloprid detected in Aeris^®-treated cotton decreased by 99.6 percent during the sampling period. For cotton seed treated with Avicta^® Duo, the mean concentrations of thiamethoxam and clothianidin in leaf tissue declined by 99.9 and 100 percent, respectively, by the time flowering occurred. There was a 99.9 percent reduction in the mean concentration of thiamethoxam by the time of flowering in leaf tissue from soybean treated with a CruiserMaxx^® seed treatment. Mean clothianidin concentrations completely diminished (®- and Poncho^®/VOTiVO^®-treated soybean plants by the time plants reached reproductive growth. The data for neonicotinoid concentrations in the soil were more variable than leaf tissue samples, and the reduction in neonicotinoid concentrations in leaf tissues did not closely correlate with concentrations in the soil. Our results suggest that neonicotinoid insecticides, when used as seed treatments in these crops, decline rapidly throughout vegetative growth stages. However, the biological impact on target or non-target arthropods was not examined.

Tarnished plant bug, Lygus lineolaris Palisot de Beauvois (Hemiptera: Miridae), has become a primary pest of cotton in the Midsouthern United States. Insect growth regulators such as novaluron are an important part of L. lineolaris management. While novaluron is lethal to nymphs, it does not kill adults, so it has been used when nymphs are the primary stage present. However, cotton yield protection was observed from an application of novaluron when adults were the predominant stage present. To explain this, a series of studies were conducted to examine sublethal impacts of novaluron to L. lineolaris adults. Novaluron ingestion by adults reduced hatch rate and sometimes reduced oviposition rate. Ingestion by either males or females reduced hatch rates, but the reduction was greater from female exposure. Contact exposure of adults with novaluron residues within 1 d of application reduced hatch rate by about 50%, but the impact on oviposition was inconsistent. A field study showed reduced hatch rate from contact exposure to mixed-age natural populations, but the overall net reproductive rate was not reduced. Surface exposure of eggs to novaluron did not reduce hatch rate. Overall, exposure of tarnished plant bug adults to novaluron, regardless of adult age or exposure route, reduced egg viability. However, the impact on oviposition rate and net reproductive rate varied with adult age and exposure route. This understanding of sublethal impacts of novaluron, in addition to lethal impacts on nymphs, should be considered when choosing application times to maximize effects on L. lineolaris populations.