Arthropod predator community associated with soybean gall midge, Resseliella maxima (Diptera: Cecidomyiidae), in Minnesotan soybean fields.

The soybean gall midge, Resseliella maxima Gagné (Diptera: Cecidomyiidae), is a pest that injures soybeans in the Midwest United States. Little is known about the natural enemies of R. maxima or the potential for biological control. Therefore, we performed a 2-yr survey in Minnesota to examine the predator community associated with R. maxima infestations. We found that Orius insidiosus (Say) (Heteroptera: Anthocoridae) and Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) were the most common foliar- and ground-foraging predators, respectively. Some of the commonly encountered predator species were tested in laboratory predation experiments. Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) and O. insidiosus represented the foliar-foraging predators tested, and H. axyridis consumed significantly more R. maxima larvae than O. insidiosus. Among the ground-foraging predators, 4 carabids were tested. Poecilus lucublandus (Say) (Coleoptera: Carabidae) and Pt. melanarius consumed significantly more R. maxima larvae than Poecilus chalcites (Say) (Coleoptera: Carabidae) and Bembidion quadrimaculatum oppositum (Say) (Coleoptera: Carabidae). We conclude that Pt. melanarius should receive further attention as a potential biological control agent of R. maxima, due to its high abundance in the soybean fields in this study, temporal overlap with the pest, and high propensity to feed on the pest.

Spatial and temporal dynamics of soybean gall midge (Resseliella maxima) parasitism by Synopeas maximum.

BACKGROUND: Soybean gall midge, Resseliella maxima Gagné (Diptera: Cecidomyiidae), is a pest that impacts soybean yield in the Midwest United States. While biological control using parasitoids may be a promising approach for managing this pest, it is crucial to have a deep understanding of parasitism dynamics to ensure effective implementation. We investigated R. maxima parasitism using a combination of three methods: rearing of field-collected hosts, dissection, and molecular assays. RESULTS: We confirmed parasitism of R. maxima by the recently described wasp Synopeas maximum Awad & Talamas (Hymenoptera: Platygastridae) and used our combinatorial approach to observe the spatial and temporal relationships between R. maxima and its parasitoid in the field. The number of R. maxima adults was greater in symptomatic plants on field edges than the field interior, but such a pattern was inconsistent for parasitism rates. Parasitism rates were generally highest early and late in the season, and lower in the middle of the season when the number of R. maxima was highest. CONCLUSION: In Minnesota, overall season-long parasitism rates of R. maxima were low (< 2%). To facilitate a wider investigation of the biological control of R. maxima, we designed a protocol for high throughput DNA extraction and quantitative polymerase chain reaction (qPCR) that can be used across a broader geography. Further research should evaluate how parasitism rates by Synopeas maximum could be promoted in production fields. © 2023 Society of Chemical Industry.

Lack of Evidence for Fitness Costs in Soybean Aphid (Hemiptera: Aphididae) With Resistance to Pyrethroid Insecticides in the Upper Midwest Region of the United States.

Twenty years after the arrival of soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in the United States, it remains the most economically important arthropod pest of soybean in the Upper Midwest Region. After years of repeated and sustained insecticidal pressures placed on the aphid, resistance to the pyrethroid class of insecticides has been documented in multiple years over a large geographic area. In this study, the fitness of aphid isolates displaying resistant and susceptible phenotypes to λ-cyhalothrin were compared within several experiments over three soybean-growing seasons. Rates of population increase were evaluated on whole plants in the greenhouse, intrinsic rates of increase were calculated from leaf discs in the laboratory, and aphid size and asymmetry were compared through tibial measurements. No evidence of a fitness cost associated with the resistant phenotype was seen in any of our experiments. In contrast, individual resistant isolates occasionally supported significantly higher fitness values than some susceptible isolates. Additionally, a pooled analysis comparing resistant and susceptible phenotypes across years and isolates revealed that, on average, the resistant phenotype had significantly higher fitness values than the susceptible phenotype in most experiments. The lack of reproductive fitness costs associated with the pyrethroid-resistant phenotype raises concerns for longevity of pyrethroid use in soybean aphid management.

Change-point analysis of lambda-cyhalothrin efficacy against soybean aphid (Aphis glycines Matsumura): identifying practical resistance from field efficacy trials.

BACKGROUND: Soybean aphid (Aphis glycines Matsumura) remains the most economically important arthropod pest of soybean in the Upper Midwest Region of the USA. Soybean aphid resistance to the pyrethroid insecticides emerged in 2015; however, the reduction in the efficacy of field applications of pyrethroid insecticides has not been quantified. Based on time-series data from insecticide efficacy trials at two locations, a novel approach of continuous two-phase change point-regression models was used to indicate whether a change in percent control had occurred, and to provide an indication of when and to what degree the percent control had changed. RESULTS: At both locations examined in this study, a significant change point for percent control of λ-cyhalothrin was detected in 2014, thus marking the onset of practical resistance in the soybean aphid. Percent control decreased at a rate of 4.30% and 19.90% per year at these locations. By contrast, percent control for chlorpyrifos remained high over time with no significant change point. CONCLUSION: This research demonstrates that retrospective time-series analysis of insecticide efficacy data can identify the onset and magnitude of practical resistance in the field. This further validates and compliments the other lines of evidence related to pyrethroid resistance in soybean aphid. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Meta-Analysis of Soybean Yield Response to Foliar Fungicides Evaluated from 2005 to 2018 in the United States and Canada.

Random-effect meta-analyses were performed on data from 240 field trials conducted between 2005 and 2018 across nine U.S. states and Ontario, Canada, to quantify the yield response of soybean after application of foliar fungicides at beginning pod (R3) stage. Meta-analysis showed that the overall mean yield response when fungicide was used compared with not applying a fungicide was 2.7% (110 kg/ha). Moderator variables were also investigated and included fungicide group, growing season, planting date, and base yield, which all significantly influenced the yield response. There was also evidence that precipitation from the time of planting to the R3 growth stage influenced yield when fungicide was used (P = 0.059). Fungicides containing a premix of active ingredients from multiple groups (either two or three ingredients) increased the yield by 3.0% over not applying a fungicide. The highest and lowest yield responses were observed in 2005 and 2007, respectively. Better yield response to fungicides (a 3.0% increase) occurred when soybean crops were planted not later than 21 May and when total precipitation between planting and the R3 application date was above historic averages. Temperatures during the season did not influence the yield response. Yield response to fungicide was higher (a 4.7% increase) in average yield category (no spray control yield 2,878 to 3,758 kg/ha) and then gradually decreased with increasing base yield. Partial economic analyses indicated that use of foliar fungicides is less likely to be profitable when foliar diseases are absent or at low levels.

Soybean aphid biotype 1 genome: Insights into the invasive biology and adaptive evolution of a major agricultural pest.

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae) is a serious pest of the soybean plant, Glycine max, a major world-wide agricultural crop. We assembled a de novo genome sequence of Ap. glycines Biotype 1, from a culture established shortly after this species invaded North America. 20.4% of the Ap. glycines proteome is duplicated. These in-paralogs are enriched with Gene Ontology (GO) categories mostly related to apoptosis, a possible adaptation to plant chemistry and other environmental stressors. Approximately one-third of these genes show parallel duplication in other aphids. But Ap. gossypii, its closest related species, has the lowest number of these duplicated genes. An Illumina GoldenGate assay of 2380 SNPs was used to determine the world-wide population structure of Ap. Glycines. China and South Korean aphids are the closest to those in North America. China is the likely origin of other Asian aphid populations. The most distantly related aphids to those in North America are from Australia. The diversity of Ap. glycines in North America has decreased over time since its arrival. The genetic diversity of Ap. glycines North American population sampled shortly after its first detection in 2001 up to 2012 does not appear to correlate with geography. However, aphids collected on soybean Rag experimental varieties in Minnesota (MN), Iowa (IA), and Wisconsin (WI), closer to high density Rhamnus cathartica stands, appear to have higher capacity to colonize resistant soybean plants than aphids sampled in Ohio (OH), North Dakota (ND), and South Dakota (SD). Samples from the former states have SNP alleles with high FST values and frequencies, that overlap with genes involved in iron metabolism, a crucial metabolic pathway that may be affected by the Rag-associated soybean plant response. The Ap. glycines Biotype 1 genome will provide needed information for future analyses of mechanisms of aphid virulence and pesticide resistance as well as facilitate comparative analyses between aphids with differing natural history and host plant range.

Implementation of a Diagnostic-Concentration Bioassay for Detection of Susceptibility to Pyrethroids in Soybean Aphid (Hemiptera: Aphididae).

Soybean aphid, Aphis glycines Matsumura, remains the most economically damaging arthropod pest of soybean in the midwestern United States and southern Canada. Foliar applications of a limited number of insecticide modes of action have been the primary management tactic, and pyrethroid resistance was documented recently with full concentration-response leaf-dip and glass-vial bioassays. Full concentration-response bioassays can be cumbersome, and a more efficient assessment tool was needed. In this study, we implemented a diagnostic-concentration glass-vial bioassay using bifenthrin and λ-cyhalothrin. Bioassays were conducted with field-collected soybean aphid populations to assess the geographic extent and severity of resistance to pyrethroids. In 2017, 10 of 18 and 11 of 21 field populations tested with bifenthrin and λ-cyhalothrin, respectively, had mean proportion mortalities less than the susceptible laboratory population. In 2018, 17 of 23 and 13 of 23 field populations tested with bifenthrin and λ-cyhalothrin, respectively, had mean proportion mortalities less than the susceptible laboratory population. Populations collected after reported field failures of a pyrethroid insecticide generally had mean proportion mortalities less than the susceptible laboratory population. In both years, there was a strong correlation between chemistries, which suggests cross-resistance between these insecticides. The diagnostic-concentration glass-vial bioassays reported here will provide the foundation for an insecticide resistance monitoring program with the ability to determine practical levels and geographic extent of insecticide resistance.

Efficacy of afidopyropen against soybean aphid (Hemiptera: Aphididae) and toxicity to natural enemies.

BACKGROUND: Soybean aphid, Aphis glycines (Hemiptera: Aphididae), remains the most significant soybean insect pest in the North Central Region of the USA. The sustainability of reliance on only a few insecticide groups for this pest is questionable. We evaluate afidopyropen, a novel pyropene insecticide (Group 9D), for efficacy against A. glycines in field and greenhouse experiments and toxicity to common natural enemies in laboratory experiments. RESULTS: Across 4 site-years of field experiments and a greenhouse experiment, afidopyropen reduced A. glycines populations similar to commonly used broad-spectrum [i.e. lambda-cyhalothrin (Group 3A) and chlorpyrifos (Group 1B)] insecticides and potential selective insecticides [i.e. sulfoxaflor (Group 4C) and flupyradifurone (Group 4D)]. In the greenhouse, however, A. glycines mortality was delayed slightly for afidopyropen compared to the other insecticides. In laboratory experiments with natural enemies of A. glycines, afidopyropen was not toxic to adult or third instar Hippodamia convergens (Coleoptera: Coccinellidae) or adult Orius insidiosus (Hemiptera: Anthocoridae), and was only moderately toxic to Aphelinus certus (Hymenoptera: Aphelinidae). CONCLUSION: Afidopyropen is effective against A. glycines and relatively non-toxic to natural enemies, and appears to be an effective option for integrated pest management and insecticide resistance management programs for A. glycines. © 2019 Society of Chemical Industry.

Impact of Single Gene and Pyramided Aphid-Resistant Soybean on Movement and Spatial Pattern of Soybean Aphid (Hemiptera: Aphididae).

Host plant resistance may be an effective option to manage soybean aphid, Aphis glycines (Matsumura) (Hemiptera: Aphididae), an important pest on soybean (Glycine max (L.) Merr.) in the U.S. Movement of soybean aphid may be altered by the presence of resistance (i.e., Rag [Resistance to Aphis glycines]) genes in soybean and changes in movement may affect the spatial pattern of a species. This study aims to assess the effects of Rag1 and pyramided Rag1+Rag2 aphid-resistant varieties on movement of soybean aphid under laboratory conditions and to evaluate potential impacts of this movement on spatial pattern of soybean aphid under field conditions. Results from the greenhouse study showed more movement of soybean aphid on both aphid-resistant varieties than the susceptible variety when aphids were placed on unifoliate leaves and no statistically significant difference in movement between Rag1 and pyramided Rag1+Rag2 varieties. When aphids were placed on new growth, movement was greater on pyramided Rag1+Rag2 than the Rag1 and susceptible variety. However, under field conditions, the spatial patterns of soybean aphid in plots with susceptible, Rag1 or pyramided Rag1+Rag2 varieties were aggregated and did not differ among varieties in vegetative and reproductive growth stages. These results are of relevance because they suggest that aspects of soybean aphid management that may be sensitive to changes in spatial pattern of the pest (e.g., natural enemy efficacy and sampling plans) may not be impacted by implementation of varieties with these resistance genes for host plant resistance.

Evidence for Soybean Aphid (Hemiptera: Aphididae) Resistance to Pyrethroid Insecticides in the Upper Midwestern United States.

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a damaging invasive pest of soybean in the upper Midwest. Threshold-based insecticide applications are the primary control method for soybean aphid, but few insecticide groups are available (i.e., pyrethroids, organophosphates, and neonicotinoids). To quantify current levels of soybean aphid susceptibility to pyrethroids in the upper Midwest and monitor for insecticide resistance, leaf-dip bioassays were performed with λ-cyhalothrin in 2013-2015, and glass-vial bioassays were performed with λ-cyhalothrin and bifenthrin in 2015 and 2016. Soybean aphids were collected from 27 population-years in Minnesota and northern Iowa, and were compared with a susceptible laboratory colony with no known insecticide exposure since discovery of soybean aphid in North America in 2000. Field-collected aphids from some locations in leaf-dip and glass-vial bioassays had significantly lower rates of insecticide-induced mortality compared with the laboratory population, although field population susceptibility varied by year. In response to sublethal concentrations of λ-cyhalothrin, adult aphids from some locations required higher concentrations of insecticide to reduce nymph production compared with the laboratory population. The most resistant field population demonstrated 39-fold decreased mortality compared with the laboratory population. The resistance documented in this study, although relatively low for most field populations, indicates that there has been repeated selection pressure for pyrethroid resistance in some soybean aphid populations. Integrated pest management and insecticide resistance management should be practiced to slow further development of soybean aphid resistance to pyrethroids.

Assessing the value and pest management window provided by neonicotinoid seed treatments for management of soybean aphid (Aphis glycines Matsumura) in the Upper Midwestern United States.

BACKGROUND: A 2-year, multi-state study was conducted to assess the benefits of using soybean seed treated with the neonicotinoid thiamethoxam to manage soybean aphid in the upper Midwestern USA and compare this approach with an integrated pest management (IPM) approach that included monitoring soybean aphids and treating with foliar-applied insecticide only when the economic threshold was reached. Concentrations of thiamethoxam in soybean foliage were also quantified throughout the growing season to estimate the pest management window afforded by insecticidal seed treatments. RESULTS: Both the IPM treatment and thiamethoxam-treated seed resulted in significant reductions in cumulative aphid days when soybean aphid populations reached threshold levels. However, only the IPM treatment resulted in significant yield increases. Analysis of soybean foliage from thiamethoxam-treated seeds indicated that tissue concentrations of thiamethoxam were statistically similar to plants grown from untreated seeds beginning at the V2 growth stage, indicating that the period of pest suppression for soybean aphid is likely to be relatively short. CONCLUSION: These data demonstrate that an IPM approach, combining scouting and foliar-applied insecticide where necessary, remains the best option for treatment of soybean aphids, both in terms of protecting the yield potential of the crop and of break-even probability for producers. Furthermore, we found that thiamethoxam concentrations in foliage are unlikely to effectively manage soybean aphids for most of the pests' activity period across the region. © 2017 Society of Chemical Industry.

Multiple Assays Indicate Varying Levels of Cross Resistance in Cry3Bb1-Selected Field Populations of the Western Corn Rootworm to mCry3A, eCry3.1Ab, and Cry34/35Ab1.

Minnesota populations of Diabrotica virgifera virgifera LeConte, the western corn rootworm, surviving Cry3Bb1-expressing corn in the field and western corn rootworm populations assumed to be susceptible to all Bt proteins were evaluated for susceptibility to Cry3Bb1, mCry3A, eCry3.1Ab, and Cry34/35Ab1 in diet assays and three different plant-based assays. Rootworm populations originating from Cry3Bb1 fields and that consistently experienced greater than expected damage had increased survival and larval growth compared to control populations assayed on Cry3Bb1 as well as mCry3a and eCry3.1Ab. Cross resistance was documented between Cry3Bb1 and both mCry3A and eCry3.1Ab as single toxins. Despite very high resistance ratios in some comparisons, cross resistance was not complete and also varied with the population being evaluated, the trait measured, and the susceptible rootworm population used for comparison. Regardless of resistance and cross resistance, all proteins, even Cry3Bb1, retained some efficacy in terms of either reducing rootworm larval growth, protecting plants from damage, or both, for all rootworm populations evaluated. For one Cry3Bb1-selected population, a resistance ratio of 9.1-fold was found to Cry34/35Ab1 when evaluating EC 50 values relative to a susceptible control population; however, resistance to Cry34/35Ab1 was not evident in all assays in this population. The United States Environmental Protection Agency recently suggested eliminating diet assays as part of the Bt resistance monitoring process. However, given the variability of responses of western corn rootworm populations to different proteins in different assays, both plant and diet assays are needed as options for detecting and fully characterizing resistance.

Non-target impacts of soybean rust fungicides on the fungal entomopathogens of soybean aphid.

Soybean aphid, Aphis glycines, has caused serious economic damage to soybean across the North Central US since its introduction to North America in 2000. The management of another invasive soybean pest, Asian soybean rust, Phakopsora pachyrhizi, using foliar fungicide applications has the potential to impact soybean aphid populations by suppressing beneficial fungal entomopathogens. In 2005 and 2006, we applied recommended soybean rust fungicide treatments, consisting of strobilurin and triazole fungicides, to small soybean plots in two locations to assess if such applications might suppress aphid fungal epizootics. In Lamberton, MN, in 2005, during the epizootic, fungicide-treated plots averaged 2.0+/-0.7% (mean+/-SE) disease prevalence while untreated plots averaged 14.2+/-5.6%. In 2007, we applied strobilurin and strobilurin-triazole mix fungicides to single-plant microplots either before or after release of Pandora neoaphidis, the most commonly observed aphid pathogen in 2005 and 2006. Treatments that contained a mixture of two active ingredients significantly lowered peak and cumulative aphid disease prevalence in both early and late reproductive stage soybeans indicating that fungicide mixtures used to manage soybean rust can negatively impact an aphid-specific fungal pathogen. However, no consistent soybean aphid population response was observed in these studies of low levels of aphid fungal infection.

Probability of cost-effective management of soybean aphid (Hemiptera: Aphididae) in North America.

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is one of the most damaging pests of soybean, Glycine max (L.) Merrill, in the midwestern United States and Canada. We compared three soybean aphid management techniques in three midwestern states (Iowa, Michigan, and Minnesota) for a 3-yr period (2005-2007). Management techniques included an untreated control, an insecticidal seed treatment, an insecticide fungicide tank-mix applied at flowering (i.e., a prophylactic treatment), and an integrated pest management (IPM) treatment (i.e., an insecticide applied based on a weekly scouting and an economic threshold). In 2005 and 2007, multiple locations experienced aphid population levels that exceeded the economic threshold, resulting in the application of the IPM treatment. Regardless of the timing of the application, all insecticide treatments reduced aphid populations compared with the untreated, and all treatments protected yield as compared with the untreated. Treatment efficacy and cost data were combined to compute the probability of a positive economic return. The IPM treatment had the highest probability of cost effectiveness, compared with the prophylactic tank-mix of fungicide and insecticide. The probability of surpassing the gain threshold was highest in the IPM treatment, regardless of the scouting cost assigned to the treatment (ranging from $0.00 to $19.76/ha). Our study further confirms that a single insecticide application can enhance the profitability of soybean production at risk of a soybean aphid outbreak if used within an IPM based system.