Tyler Towles

In the southern United States, thrips are a significant early season pest of cotton. In the United States, in 2022, 98% of cotton acres were infested with thrips, and, of those acres, 45% were treated for thrips. Thrips injury resulted in over $113 million dollars in losses plus control costs to the cotton industry in the United States that year. A new Bacillus thuringiensis trait known as ThryvOn has been commercialized to provide control against thrips. There is ongoing debate about the need for an insecticidal seed treatment to improve thrips control on ThryvOn varieties. Field studies were conducted to determine if the addition of an imidacloprid seed treatment improved efficacy against tobacco thrips and to determine if reduced rates of seed treatments (0, 25, 50, 75, and 100% of the labeled rate) provided benefits for thrips control in ThryvOn cotton. To control for infestation pressure, a complementary greenhouse study was conducted using the same treatments under controlled conditions. Imidacloprid provided only a limited benefit for improved management on ThryvOn cotton in the greenhouse study, but no benefit in the field study. Efforts in pest surveillance should be continued in ThryvOn cotton to allow for foliar applications when warranted based on established thresholds. No conclusions can be drawn about the benefits of an imidacloprid seed treatment for resistance management in ThryvOn cotton from this study, but these data suggest that any benefit would be minimal.

The establishment of invasive species populations can threaten the ecological balance in naïve habitats and impact agricultural production practices. Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) (old-world bollworm, OWBW) and Helicoverpa zea (corn earworm, CEW) were geographically separated prior to the 2013 report of OWBW invasion into South America. Introgression of OWBW-specific cytochrome P450 337B3 (CYP337B3) gene into CEW was repeatedly detected across South America and the Caribbean. Two hybrids were documented from Texas in 2019. In this study, screening insects collected in Olathe, CO, USA, where a failure of pyrethroids to control CEW damage to conventional sweetcorn in 2023 detected 28.6% of insects with the OWBW-specific CYP337B3 marker. Nucleotide sequencing of the CYP337B3 gene identified 73.1% and 26.9% of insects carried CYP337B3v2 and CYP337B3v6 alleles, respectively, and 0.15 overall frequency of CYP337B3 alleles. Based on prior data for distinct phylogeographic origins of CYP337B3v2 and v6 alleles, our results indicate Olathe samples were derived from 2 different introductions: An uncertain source of the v6 allele that was initially reported in West Africa and possibly South American or Caribbean origin of the globally distributed v2 allele. One of the 1618 individuals screened also carried a ribosomal RNA internal transcribed spacer 1 derived from OWBW. Local selection pressures at the Olathe location imposed by repeated pyrethroid exposures are likely attributed to the prevalence of CYP337B3, where control practices hasten the accumulation of phenotypic resistance by adaptive introgression. Pyrethroid and other resistance factors carried by invasive OWBW may continue to impact CEW management tactics across the Americas.

Neonicotinoid insecticide seed treatments are commonly used in rice (Oryza sativa) production to control rice water weevil (Lisorhoptrus oryzophilus). With the use of neonicotinoid seed treatments, there is potential that honey bees (Apis mellifera) could be exposed to neonicotinoids through translocation to the pollen. Studies were conducted in 2015 and 2016 to determine the level of neonicotinoids present in flag leaves, pollen, and grain of rice. Thiamethoxam was applied as a seed treatment and foliar prior to flooding. Clothianidin was applied as a seed treatment and as a foliar at a preflood and postflood timing. Subsamples of flag leaves, pollen, and grain were analyzed for positive neonicotinoid detections and abundance. Thiamethoxam was detected in 8.9% of samples and clothianidin was detected in 1.4% of samples. For both thiamethoxam and clothianidin, more positive samples were observed in flag leaf samples than in pollen or grain. An average of 4.30 ng/g of thiamethoxam was detected in flag leaves from seed-applied thiamethoxam. An average of 1.25 ng/g of clothianidin was found in flag leaves from a preflood application of clothianidin. A survey of honey bees present in rice fields was conducted in Mississippi and Arkansas to determine the abundance of honey bees present in rice fields based on the time of day. Honey bee densities were low in rice, with less than 5% and 3% positive detections observed in Mississippi and Arkansas, respectively. More positive detections and higher densities of honey bees were observed for mid-day sampling than for morning or evening sampling.

The redbanded stink bug, Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae), is a significant soybean pest in the Americas, inflicting more physical damage on soybean than other native stink bugs. Studies suggest that its heightened impact is attributed to the aggressive digestive properties of its saliva. Despite its agricultural importance, the factors driving its greater ability to degrade plant tissues have remained unexplored in a genomic evolutionary context. In this study, we hypothesized that lineage-specific gene family expansions have increased the copy number of digestive genes expressed in the salivary glands. To investigate this, we annotated a previously published genome assembly of the redbanded stink bug and performed a comparative genomic analysis on 11 hemipteran species and reconstructed patterns of gene duplication, gain, and loss in the redbanded stink bug. We also performed RNA-seq on the redbanded stink bug’s salivary tissues, along with the rest of the body without salivary glands. We identified hundreds of differentially expressed salivary genes, including a subset lost in other stink bug lineages but retained and expressed in the redbanded stink bug’s salivary glands. These genes were significantly enriched with protein families involved in proteolysis, potentially explaining the redbanded stink bug’s heightened damage to soybeans. Contrary to our hypothesis, we found no support for an increased copy number of digestive genes in the salivary glands of the redbanded stink bug. Nonetheless, these results provide insight into the evolution of this important crop pest, establishing a link between its genomic history and its agriculturally important physiology.

For non-native insects that are economically damaging, understanding the drivers of range expansions and contractions is important for forecasting pest pressure. The invasion of the redbanded stink bug, Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae), reached Louisiana, United States, in 2000, after which the northern range limits of this species have fluctuated annually. Low winter temperatures have been implicated as a major driver of this pattern, but the importance of cold temperatures—or other abiotic factors—for the persistence of this pest over large geographic scales are incompletely understood. We coupled occurrence data of P. guildinii with climatic data to investigate trends in P. guildinii presence in relation to winter temperatures and develop species distribution models, forecasting habitat suitability based on current and future climatic scenarios. Our results show that (i) some P. guildinii persisted in locations where ambient temperatures reached −12°C, (ii) overwintering temperatures drive P. guildinii range dynamics, and (iii) with intermediate projections of climatic warming, northward expansion by P. guildinii in North America is likely to be minimal. While the northern extent of P. guildinii’s range may now be largely realized in North America, our results suggest that increased frequency of mild winters could reduce interannual fluctuations of P. guildinii and enable it to become a more consistent economic concern for soybean growers throughout the Midsouth region of the United States.

The establishment of invasive species populations can threaten the ecological balance in naïve habitats and impact agricultural production practices. Helicoverpa armigera (old-world bollworm, OWBW) and H. zea (corn earworm, CEW) were geographically separated prior to the 2013 report of OWBW invasion into South America. Introgression of OWBW-specific cytochrome P450 337B3 (CYP337B3) gene into CEW was repeatedly detected across South America and the Caribbean. Two hybrids were documented from Texas in 2019. In this study, screening insects collected in Olathe, Colorado, USA, where a failure of pyrethroids to control CEW damage to conventional sweetcorn in 2023 detected 28.6% of insects with the OWBW-specific CYP337B3 marker. Nucleotide sequencing of the CYP337B3 gene identified 73.1 and 26.9% of insects carried CYP337B3v2 and CYP337B3v6 alleles, respectively and 0.15 overall frequency of CYP337B3 alleles. Based on prior data for distinct phylogeographic origins of CYP337B3v2 and v6 alleles, our results indicate Olathe samples were derived from two different introductions; An uncertain source of the v6 allele that was initially reported in West Africa and possibly South American or Caribbean origin of the globally distributed v2 allele. One of the 1618 individuals screened also carried a ribosomal RNA internal transcribed spacer 1 (ITS1) derived from OWBW. Local selection pressures at the Olathe location imposed by repeated pyrethroid exposures are likely attributed to the prevalence of CYP337B3, where control practices hasten the accumulation of phenotypic resistance by adaptive introgression. Pyrethroid and other resistance factors carried by invasive OWBW may continue to impact CEW management tactics across the Americas.

On 19 August 2022, a soybean looper insecticide efficacy trial was conducted at Delta Research and Extension Center in Stoneville, Mississippi to evaluate the performance of 5 insecticides compared to an untreated check. Field studies were implemented as a randomized complete block with 4 replications. Field studies were implemented as a randomized complete block with 4 replications. All plots received applications with a MUDMASTER, 4WD Multi-Purpose Sprayer, (Bowman manufacturing, Newport, AR) equipped with a compressed air high clearance mounted multi-boom calibrated to deliver 10 gallons per acre at 50 PSI using TX-6 Hollow Cone nozzles (2 nozzles per row) (TeeJet Technologies, Glendale, IL). Soybean loopers were sampled 5, 10, 12, and 19 DAT by taking 25 sweeps with per plot with a 38.1-cm diameter sweep net. Percent defoliation in each plot was visually estimated at 19 DAT. Data were analyzed using ANOVA and means were separated using Fisher’s protected LSD (P ≤ 0.05).

On 29 Mar 2022, an at-planting insecticide seed treatment trial was planted at the Delta Research and Extension Center in Stoneville, Mississippi to evaluate commonly used corn insecticide seed treatments at varying rates for stand uniformity and southern corn rootworm efficacy. Plot sizes were 4 rows wide by 40 feet in length on 40 inch centers. Field studies were implemented as a randomized complete block with 4 replications. Stand counts were measured and stunted plant estimates were conducted at 13 and 28 days after emergence (DAE). At each sample date, all plants and all stunted plants on the center 2 rows were counted in each plot. These values were converted to plants per acre. Grain yield was determined by harvesting the center 2 rows of each plot with a small plot combine. Yields were adjusted to 15% moisture content and converted to bu/acre. Data were subjected to ANOVA and means separated according to Fisher’s protected least significant difference.

On 29 Apr 2022, an at-planting insecticide seed treatment trial was planted at the Delta Research and Extension Center in Stoneville, Mississippi to evaluate the impact of commonly used insecticide seed treatments on soybean stand establishment. All treatments, except the untreated check, included at least one fungicide product in addition to the insecticide component. The same fungicide was not used for all treatments because commercial premixes of insecticide and fungicide products were used in some cases. Plot sizes were 4 rows wide by 40 feet in length on 40-inch centers. Field studies were implemented as a randomized complete block with 4 replications. Stand counts were conducted 8 and 23 days after emergence (DAE). At each sample date, all plants on the center 2 rows of each plot were counted. These were converted to total plant stand per acre. Data were subjected to ANOVA and means were separated according to Fisher’s protected least significant difference (FPLSD).

Redbanded stink bug is the most problematic pest within the stink bug complex in soybean production in Mississippi. A trial was conducted at Mississippi State University’s Delta Research and Extension Center in Stoneville, Mississippi, to evaluate the performance of selected insecticides against redbanded stink bug. Plot size was 4 rows by 40 feet long on 40-inch rows in a randomized complete block design with 4 replications. Insecticide treatments were applied on 13 Sep with a Mudmaster high-clearance sprayer with TX-6 hollow cone tips calibrated to 10 GPA at 60 PSI. Insect numbers were taken at 3, 6, 10, 14, and 37 DAT by taking 25 sweeps per plot. Data were analyzed with SAS 9.4 using ANOVA, and a Fisher’s Protected LSD test to separate means (P < 0.05).