Search

Foliar application of insecticides is the main strategy to manage soybean aphid, Aphis glycines (Hemiptera: Aphididae), in the northcentral United States. Subpopulations of A. glycines have multiple nonsynonymous mutations in the voltage-gated sodium channel (vgsc) genes that are associated with pyrethroid resistance. We explored if fitness costs are associated with phenotypes conferred by vgsc mutations using life table analyses. We predicted that there would be significant differences between pyrethroid susceptibility and field-collected, parthenogenetic isofemale clones with differing, nonsynonymous mutations in vgsc genes.Estimated resistance ratios for the pyrethroid-resistant clones ranged from 3.1 to 37.58 and 5.6 to 53.91 for lambda-cyhalothrin and bifenthrin, respectively. Although life table analyses revealed some biological and demographic parameters to be significantly different among the clonal lines, there was no association between levels of pyrethroid resistance and a decline in fitness. By contrast, one of the most resistant clonal lines (SBA-MN1-2017) had a significantly higher finite rate of increase, intrinsic rate of increase and greater overall fitness compared to the susceptible control and other pyrethroid-resistant clonal lines.Our life history analysis suggests that there are no negative pleotropic effects associated with the pyrethroid resistance in the clonal A. glycines lines used in this study. We discuss the potential impact of these results on efficacies of insecticide resistance management (IRM) and integrated pest management (IPM) plans directed at delaying the spread of pyrethroid-resistant A. glycines.

The green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), is a key insect pest of amaranth in East Africa. Pest management has been restricted to indiscriminate application of insecticides to foliage. Applying systemic insecticides to seeds has been shown to manage aphid infestations in other crop systems. We evaluated two commercially available seed treatments in East Africa, Apron Star (thiamethoxam 20 g/kg + metalaxyl-M 20 g/kg + difenoconazole 2 g/kg) and Menceron (imidacloprid 233 g/L + pencycuron 50 g/L + thiram 107 g/L) for their efficacy against M. persicae and impact on fresh leaf yield with two Amaranthus species, Amaranthus blitum (2 selections), Amaranthus hybridus (4 selections) and untreated control. Two storage periods (24 h and 3 months) with seed treatments were used. Each amaranth selection was treated individually with Apron and Monceren or untreated, and seeds were planted either 24 h or 3 months after treatment. Significant reduction in live aphids was observed with A. blitum and A. hybridus selections grown with seed treatment, at 6, 8 and 10 d after infestation (DAI) when compared with seeds grown without seed treatment. Untreated seeds of A. hybridus (selection 5) had significantly higher number of live aphids up to 243, greater percentage of damaged leaves and leaf damage score up to 84% and 64% respectively when compared with treated seeds of specific amaranth at 10 DAI. No significant difference was noted between seed treatment and storage time. Amaranth seeds treated with Monceren offered more protection against infestations of Myzus persicae than amaranth seeds treated with Apron under high tunnel experiments.

Extreme weather events, like high temperatures and droughts, are predicted to become common with climate change, and may negatively impact plant growth. How honey bees (Apis mellifera L. [Hymenoptera: Apidae]) will respond to this challenge is unclear, especially when collecting pollen, their primary source of protein, lipids, and micro-nutrients. We explored this response with a data set from multiple research projects that measured pollen collected by honey bees during 2015–2017 in which above-average temperatures and a drought occurred in 2017. We summarized the abundance and diversity of pollen collected from July to September in replicated apiaries kept at commercial soybean and corn farms in Iowa, in the Midwestern USA. The most commonly collected pollen was from clover (Trifolium spp. [Fabales: Fabaceae]), which dramatically declined in absolute and relative abundance in July 2017 during a period of high temperatures and drought. Due to an apparent lack of clover, honey bees switched to the more drought-tolerant native species (e.g., Chamaecrista fasciculata [Michx.] Greene [Fabales: Fabaceae], Dalea purpurea Vent. [Fabales: Fabaceae], Solidago spp. [Asterales: Asteraceae]), and several species of Asteraceae. This was especially noticeable in August 2017 when C. fasciculata dominated (87%) and clover disappeared from bee-collected pollen. We discuss the potential implications of climate-induced forage dearth on honey bee nutritional health. We also compare these results to a growing body of literature on the use of native, perennial flowering plants found in Midwestern prairies for the conservation of beneficial insects. We discuss the potential for drought resistant-native plants to potentially promote resilience to climate change for the non-native, managed honey bee colonies in the United States.

As the expansion of solar power spreads through much of the United States, members of the solar industry are working to change how solar energy facilities are designed and presented to the public. This includes the addition of habitat to conserve pollinators. We highlight and discuss ongoing efforts to couple solar energy production with pollinator conservation, noting recent legal definitions of these practices. We summarize key studies from the field of ecology, bee conservation, and our experience working with members of the solar industry (e.g., contribution to legislation defining solar pollinator habitat). Several recently published studies that employed similar practices to those proposed for solar developments reveal features that should be replicated and encouraged by the industry. These results suggest the addition of native, perennial flowering vegetation will promote wild bee conservation and more sustainable honey beekeeping. Going forward, there is a need for oversight and future research to avoid the misapplication of this promising but as of yet untested practice of coupling solar energy production with pollinator-friendly habitat. We conclude with best practices for the implementation of these additions to realize conservation and agricultural benefits.

The soybean aphid (Aphis glycines) is an important pest of soybeans in the Midwestern US. The first aphid resistance genes were identified in the early 21st century and resistant varieties have been commercially available for 10 years, but have been very underutilized. Major seed companies have avoided commercializing aphid resistant soybean varieties for conventional farmers (i.e., not organic), in part because of the discovery of virulent biotypes in North America. The emergence of soybean aphid populations resistant to insecticides creates a greater incentive for the use of host plant resistance. New research on aphid genetics and markers, plant gene expression and in-plant refuges, suggest important avenues for insect resistance management (IRM) which may encourage more widescale commercialization of this valuable pest management tool.

BACKGROUND The profitability of farming varies based on factors such as a crop's market value, input costs and occurrence of resistant pests, all capable of altering the value of pest management tactics in an integrated pest management program. We provide a framework for calculating expected yield and expected net revenue of pest management scenarios, using the soybean aphid (Aphis glycines) as a case study. Foliar insecticide and host‐plant resistance are effective management tactics for preventing yield loss from soybean aphid outbreaks; however, pyrethroid‐resistant aphid populations pose a management challenge for farmers. We evaluated eight scenarios relevant to soybean aphid management in Iowa with varying probabilities of aphid outbreaks and insecticide‐resistant aphids occurring. RESULTS Our equation suggests that insecticide use is profitable when the probability of an aphid outbreak is ≥29%, and soybean production will become more costly with increasing probability of pyrethroid‐resistant aphids. If farmers continue to use pyrethroids, they will not experience financial consequences from pyrethroid‐resistant aphids until the chance of insecticide resistance is 48%. Aphid‐resistant varieties provided consistent yield and offered the highest net revenue under all conditions. CONCLUSION This framework can be used for other crop–pest systems to evaluate the profitability of management tactics and investigate how resistance impacts revenue for farmers. Including the cost of resistance in crop budgets can help farmers and agronomic consultants comprehend these impacts and enhance decision‐making to increase revenue and curb resistance development., We developed a framework to evaluate the profitability of management scenarios across varying probabilities of a pest outbreak occurring and probabilities that the pest is resistant to the management tactic.

Fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is the main pest of maize in Brazil, attacking plants from emergence to reproductive stages. Here, we conducted studies to evaluate the efficacy of two seed treatments (chlorantraniliprole alone and imidacloprid combined with thiodicarb) on Bt and non-Bt maize in laboratory bioassays with distinct FAW strains that are susceptible, selected for resistance to Bt-maize single (Cry1F) or pyramided (Cry1A.105 + Cry2Ab2) events and F1 hybrids of the selected and susceptible strains (heterozygotes), and in the field against a natural infestation. In the laboratory, leaf-discs from seed treated Bt-maize plants at 7 d after emergence (DAE) increased the mortality of FAW resistant, heterozygote, and susceptible strains up to 24.8%, when compared with the respective maize grown without a seed treatment. In the field against natural infestations of FAW, Bt maize with a seed treatment had ~30% less FAW damage than non-Bt maize with the same seed treatment at 7 and 14 DAE. No differences in FAW damage was observed between Bt and non-Bt maize grown with and without a seed treatment at 21 DAE. Maize seeds treated with chlorantraniliprole alone or imidacloprid and thiodicarb combined presented limited protection against early infestations of FAW strains under laboratory and field studies.

Intensified agriculture reduces natural and seminatural habitats and plant diversity, reducing forage available to honey bees (Apis mellifera L. [Hymenoptera: Apidea]). In agricultural landscapes of Iowa, United States, we studied the impact of extrinsic agricultural intensification on the availability of pollen for honey bees by placing colonies next to soybean fields surrounded by either a low or high level of cultivation. The abundance and diversity of pollen returned to a colony were estimated by placing pollen traps on bee colonies during the summer and fall of 2015 and 2016. We observed no difference in abundance and diversity of pollen collected by colonies in either landscape, but abundance varied over time with significantly less collected in September. We explored if the most commonly collected pollen from these landscapes had the capacity to support honey bee immune health by testing if diets consisting of these pollens improved bee resistance to a viral infection. Compared to bees denied pollen, a mixture of pollen from the two most common plant taxa (Trifolium spp. L. [Fabales: Fabaceae] and Chimaechrista fasciculata (Michx.) Greene [Fabales: Fabaceae]) significantly reduced honey bee mortality induced by viral infection. These data suggest that a community of a few common plants was favored by honey bees, and when available, could be valuable for reducing mortality from a viral infection. Our data suggest a late season shortage of pollen may be ameliorated by additions of fall flowering plants, like goldenrod (Solidago spp. L. [Asterales: Asteraceae]) and sunflower (Helianthus, Heliopsis, and Silphium spp. [Asterales: Asteraceae]), as options for enhancing pollen availability and quality for honey bees in agricultural landscapes.

In the last century, a global transformation of Earth’s surface has occurred due to human activity with extensive agriculture replacing natural ecosystems. Concomitant declines in wild and managed bees are occurring, largely due to a lack of floral resources and inadequate nutrition, caused by conversion to monoculture-based farming. Diversified fruit and vegetable farms may provide an enhanced variety of resources through crops and weedy plants, which have potential to sustain human and bee nutrition. We hypothesized fruit and vegetable farms can enhance honey bee (Hymenoptera: Apidae, Apis mellifera Linnaeus) colony growth and nutritional state over a soybean monoculture, as well as support a more diverse wild bee community. We tracked honey bee colony growth, nutritional state, and wild bee abundance, richness, and diversity in both farm types. Honey bees kept at diversified farms had increased colony weight and preoverwintering nutritional state. Regardless of colony location, precipitous declines in colony weight occurred during autumn and thus colonies were not completely buffered from the stressors of living in a matrix dominated with monocultures. Contrary to our hypothesis, wild bee diversity was greater in soybean, specifically in August, a time when fields are in bloom. These differences were largely driven by four common bee species that performed well in soybean. Overall, these results suggest fruit and vegetable farms provide some benefits for honey bees; however, they do not benefit wild bee communities. Thus, incorporation of natural habitat, rather than diversified farming, in these landscapes, may be a better choice for wild bee conservation efforts.

The green peach aphid [Myzus persicae (Sulzer)] is an important pest of amaranth grown for leaf consumption (i.e., leafy amaranth) in the tropics. Aphids reduce the amount of fresh leaf yield of amaranth and the value of leafy amaranth as aphid-infested leaves are not marketable. Our objective was to evaluate Amaranthus species selected by a breeding program in East Africa to develop cultivars for leaf consumption with resistance to M. persicae. We focused on antibiosis to determine whether varieties of Amaranthus spp. could be grown without producing an aphid population. Artificial infestations of aphids were placed on multiple selections of three species of Amaranthus: two selections of A. blitum, four selections of A. hybridus and one selection of A. hypochondriacus. Aphid populations were assessed over a 5-wk period. Evaluations of vegetative yield, leaf damage symptoms, and specific leaf area (SLA) were made of the seven selections at the end of this experiment. Aphid populations assessed 49 d after planting differed significantly (P ≤ 0.001) among the amaranth species and within selections of the same species. The selections of A. blitum had the lowest aphid populations, and A. hybridus had the highest populations. Selections of A. hybridus produced the most marketable leaves (i.e., aphid free). The fresh weight of A. blitum were the lowest of the seven selections, whereas A. hybridus had the greatest fresh leaf weight. Implications of these finding for further promotion of amaranth breeding are discussed related to pest management for leaf production.

Disturbances associated with agricultural intensification reduce our ability to achieve sustainable crop production. These disturbances stem from crop-management tactics and can leave crop fields more vulnerable to insect outbreaks, in part because natural-enemy communities often tend to be more susceptible to disturbance than herbivorous pests. Recent research has explored practices that conserve natural-enemy communities and reduce pest outbreaks, revealing that different components of agroecosystems can influence natural-enemy populations. In this review, we consider a range of disturbances that influence pest control provided by natural enemies and how conservation practices can mitigate or counteract disturbance. We use four case studies to illustrate how conservation and disturbance mitigation increase the potential for biological control and provide co-benefits for the broader agroecosystem. To facilitate the adoption of conservation practices that improve top-down control across significant areas of the landscape, these practices will need to provide multifunctional benefits, but should be implemented with natural enemies explicitly in mind.

The north central state of Iowa is heavily dominated by agriculture, with limited nesting and foraging habitat for wild and managed pollinators. This region has been identified as critical for pollinator conservation for bees and non-bee species (e.g., monarch butterfly [Danaus plexippus]). Pollinator sustainability (i.e., wild bee conservation and sustainable beekeeping) relies upon management decisions by beekeepers, farmers, and landowners, but it is unclear if these stakeholders are aware of and use best practices. We present results of surveys administered to Iowan beekeepers, farmers, and landowners after extension programming on best management practices for sustaining honey bees (Apis mellifera) and other pollinators. Results show beekeepers, farmers, and landowners believe implementing pollinator-friendly practices is important. However, knowledge of tools to implement these practices, such as registering apiaries to avoid pesticide drift or cost-share programs for establishing habitat on their land, was very low. These results suggest opportunities exist for connecting beekeepers seeking higher quality apiaries with landowners that have established habitat with added floral resources. Further, we reviewed practices that reconstruct tallgrass prairie with support of federal cost-share funds, specifically CP42 and CP43 of the USDA’s conservation reserve program. Overall, we document strong support and enthusiasm for pollinator-friendly practices in Iowa but note gaps in knowledge of practices that are most effective and what tools are available to implement them. These results suggest a way for pollinator extension programs to address these knowledge gaps in a receptive group of beekeepers, farmers, and landowners.

The frequent use of insecticides to manage soybean aphids, Aphis glycines (Hemiptera: Aphididae), in the United States has contributed to field-evolved resistance. Pyrethroid-resistant aphids have nonsynonymous mutations in the voltage-gated sodium channel (vgsc). We identified a leucine to phenylalanine mutation at position 1014 (L1014F) and a methionine to isoleucine mutation (M918I) of the A. glycines vgsc, both suspected of conferring knockdown resistance (kdr) to lambda-cyhalothrin. We developed molecular markers to identify these mutations in insecticide-resistant aphids. We determined that A. glycines which survived exposure to a diagnostic concentration of lambda-cyhalothrin and bifenthrin via glass-vial bioassays had these mutations, and showed significant changes in the resistance allele frequency between samples collected before and after field application of lambda-cyhalothrin. Thus, a strong association was revealed between aphids with L1014F and M918I vgsc mutations and survival following exposure to pyrethroids. Specifically, the highest survival was observed for aphids with the kdr (L1014F) and heterozygote super-kdr (L1014F + M918I) genotypes following laboratory bioassays and in-field application of lambda-cyhalothrin. These genetic markers could be used as a diagnostic tool for detecting insecticide-resistant A. glycines and monitoring the geographic distribution of pyrethroid resistance. We discuss how generating these types of data could improve our efforts to mitigate the effects of pyrethroid resistance on crop production.

Significance Industrial-scale production of crops through monocultures has resulted in “green deserts” of reduced biodiversity in many areas worldwide. Such simplified landscapes may impact ecosystem services such as pollination. Here, we present a large-scale, longitudinal study of managed honey bee colonies in the context of corn and soybean monocultures. Our results reveal a brief burst of colony growth during soybean bloom, followed by a longer period of forage dearth, resulting in decline in several aspects of honey bee health at both colony and individual levels. We demonstrate this decline is reversible when honey bees have access to native, perennial plants (i.e., prairie). Our results suggest sustainable pollinator management in landscapes dominated by monocultures can be achieved through reintegration of native biodiversity., Intensive agriculture can contribute to pollinator decline, exemplified by alarmingly high annual losses of honey bee colonies in regions dominated by annual crops (e.g., midwestern United States). As more natural or seminatural landscapes are transformed into monocultures, there is growing concern over current and future impacts on pollinators. To forecast how landscape simplification can affect bees, we conducted a replicated, longitudinal assessment of honey bee colony growth and nutritional health in an intensively farmed region where much of the landscape is devoted to production of corn and soybeans. Surprisingly, colonies adjacent to soybean fields surrounded by more cultivated land grew more during midseason than those in areas of lower cultivation. Regardless of the landscape surrounding the colonies, all experienced a precipitous decline in colony weight beginning in August and ended the season with reduced fat stores in individual bees, both predictors of colony overwintering failure. Patterns of forage availability and colony nutritional state suggest that late-season declines were caused by food scarcity during a period of extremely limited forage. To test if habitat enhancements could ameliorate this response, we performed a separate experiment in which colonies provided access to native perennials (i.e., prairie) were rescued from both weight loss and reduced fat stores, suggesting the rapid decline observed in these agricultural landscapes is not inevitable. Overall, these results show that intensively farmed areas can provide a short-term feast that cannot sustain the long-term nutritional health of colonies; reintegration of biodiversity into such landscapes may provide relief from nutritional stress.

Farmers face many choices when selecting seed for soybean (Glycine max (L.) Merr.) production, including highly desired herbicide tolerance traits. Despite the convenience of herbicide tolerance, resistant weeds and technology fees may reduce utility and profitability of these varieties, especially when commodity prices are low. Sporadic outbreaks of soybean aphid (Aphis glycines Matsumura, Hemiptera: Aphididae) that require insecticide use for optimal yield can be a further complication for farmers in Iowa. Soybean aphid-resistant varieties are commercially available, but in limited genetic backgrounds without herbicide tolerance. We hypothesized yield and value of resistance traits will vary based on the environment. We established plots at two locations with different risks of soybean aphid outbreaks and used two planting dates at each location to mimic different yield environments. In 2016 and 2017, we planted four varieties that varied in their susceptibility to soybean aphids and glyphosate, and applied insecticides if aphid populations reached an economic threshold. Regardless of genetic background, aphid-resistant varieties prevented populations from reaching the economic threshold at all environments. We observed no significant difference in yield between resistant and susceptible varieties, revealing this trait is as effective at protecting yield as an insecticide application on susceptible varieties at the high-risk location. We also explored the value of each variety in different environments. Resistant varieties produced greater potential net revenue than susceptible varieties at the high-risk location, while the opposite occurred at the low-risk location. Resistant varieties with herbicide tolerance, if made available, would be the most valuable across all environments.

The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is an invasive pest that can cause severe yield loss to soybeans in the northcentral United States. A tactic to counter this pest is the use of aphid-resistant soybean varieties. However, the occurrence of virulent biotypes can alter plant physiology and impair the use of this management strategy. Soybean aphids can alter soybean physiology primarily by two mechanisms, feeding facilitation and the obviation of resistance, favoring subsequent colonization by additional conspecifics. We developed a non-local, differential equation population model, to explore the dynamics of these biological mechanisms on soybean plants co-infested with virulent and avirulent aphids. We then use demographic parameters from laboratory experiments to perform numerical simulations via the model. These simulations successfully mimic various aphid dynamics observed in the field. Our model showed an increase in colonization of virulent aphids increases the likelihood that aphid-resistance is suppressed, subsequently increasing the survival of avirulent aphids, producing an indirect, positive interaction between the biotypes. These results suggest the potential for a "within plant" refuge that could contribute to the sustainable use of aphid resistant soybeans., Comment: 15 pages, 3 figures, 2 tables, Accepted in Journal of Economic Entomology

Populations of wild and managed pollinators are declining in North America, and causes include increases in disease pressure and decreases in flowering resources. Tallgrass prairies can provide floral resources for managed honey bees (Hymenoptera: Apidae, Apis mellifera Linnaeus) and wild bees. Honey bees kept near prairies may compete with wild bees for floral resources, and potentially transfer viral pathogens to wild bees. Measurements of these potential interactions are lacking, especially in the context of native habitat conservation. To address this, we assessed abundance and richness of wild bees in prairies with and without honey bee hives present, and the potential spillover of several honey bee viruses to bumble bees (Hymenoptera: Apidae, Bombus Latrielle). We found no indication that the presence of honey bee hives over 2 yr had a negative effect on population size of wild bee taxa, though a potential longer-term effect remains unknown. All levels of viruses quantified in bumble bees were lower than those observed in honey bees. Higher levels of deformed wing virus and Israeli acute paralysis virus were found in Bombus griseocollis DeGeer (Hymenoptera: Apidae) collected at sites with hives than those without hives. These data suggest that the presence of honey bees in tallgrass prairie could increase wild bee exposure to viruses. Additional studies on cross-species transmission of viruses are needed to inform decisions regarding the cohabitation of managed bees within habitat utilized by wild bees.

Premise Trichomes are hair‐like appendages extending from the plant epidermis. They serve many important biotic roles, including interference with herbivore movement. Characterizing the number, density, and distribution of trichomes can provide valuable insights on plant response to insect infestation and define the extent of plant defense capability. Automated trichome counting would speed up this research but poses several challenges, primarily because of the variability in coloration and the high occlusion of the trichomes. Methods and Results We developed a simplified method for image processing for automated and semi‐automated trichome counting. We illustrate this process using 30 leaves from 10 genotypes of soybean (Glycine max) differing in trichome abundance. We explored various heuristic image‐processing methods including thresholding and graph‐based algorithms to facilitate trichome counting. Of the two automated and two semi‐automated methods for trichome counting tested and with the help of regression analysis, the semi‐automated manually annotated trichome intersection curve method performed best, with an accuracy of close to 90% compared with the manually counted data. Conclusions We address trichome counting challenges including occlusion by combining image processing with human intervention to propose a semi‐automated method for trichome quantification. This provides new opportunities for the rapid and automated identification and quantification of trichomes, which has applications in a wide variety of disciplines.

To study how honey bees utilize forage resources and guide pollination management plans in crops, a multitude of methods have been developed, but most are time consuming, costly, and require specialized skills. Colored pan traps for monitoring activity-density are a simple, efficient, and cost-effective alternative, however, their usefulness for studying honey bees is not well described. We examined if trap color, location within a field, and the presence of managed colonies affected estimates of honey bee activity-density within soybean fields. Soybeans are visited by pollinators but do not require these visits for seed development. Pan traps, especially those colored blue, captured more honey bees when colonies were present. There were no differences in activity-density based on placement of traps within a field nor with increasing distance from colonies. Throughout the season, activity-density in soybeans was constant but tripled after soybean ceased blooming, suggesting spikes in pan trap captures may indicate periods of forage scarcity. Activity-density did not correlate with the population size of worker bees at a site, but did correlate with number of colonies present. We conclude that pan traps can be useful for assessing honey bee activity, particularly for estimating colony presence and identifying times of forage scarcity.

International audience; 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.

Adding habitat within agricultural ecosystems is necessary to reverse declines in pollinator abundance and diversity. Understanding pesticide exposure to pollinator habitat near crop fields is necessary to support risk assessments. Neonicotinoids applied to maize and soybean seeds can be transported from crop fields to adjacent habitat through dust drift during planting and/or through overland runoff or subsurface flow following planting. Pollinators, especially bees (e.g. Apidae) and monarch butterflies (Danaus plexippus), could be exposed to neonicotinoids through ingestion of contaminated plant material (e.g. milkweed leaves). Neonicotinoids have been detected in pollinator-attractive habitats near crop fields; however, the magnitude and seasonal variation of the concentration of these insecticides has not been determined. We quantified concentrations of clothianidin, thiamethoxam, and imidacloprid in soil and forb leaf tissue, including milkweed (Asclepias spp.) located within reconstructed prairies (3–4 years post-establishment) within or adjacent to maize or soybean fields. Samples taken from April through August in 2017 and 2018 were analyzed with liquid chromatography-tandem mass spectrometry; 100% of soil, 80% of vegetation from blooming forbs, and 80% of milkweed leaf tissue samples had at least one neonicotinoid present above the method detection limit (0.07–0.9 ng g-1). The maximum concentrations detected in 2017 or 2018 of clothianidin, thiamethoxam, and imidacloprid in milkweed leaf tissue samples were 6.6, 12.9, and 2.8 ng g-1, respectively. These values are 10 to 130-fold lower than the chronic LC10 values for monarch larvae, indicating it is unlikely that this route of neonicotinoid exposure will cause adverse effects to monarch larvae.

Since the discovery of Aphis glycines Matsumura (Hemiptera: Aphididae) in the United States, the primary management tactic has been foliar insecticides. Alternative management options such as host plant resistance to A. glycines have been developed and their effectiveness proved. However, the use of host plant resistance was complicated by the discovery of multiple, virulent biotypes of A. glycines in the United States that are capable of overcoming single Rag genes, Rag1 and Rag2, as well as a two-gene pyramid of Rag1+Rag2. However, current models predict that the virulent allele frequency of A. glycines decreases in response to the use of pyramided Rag genes, suggesting that pyramids represent a more sustainable use of these traits. Previous research has demonstrated that virulent biotypes can be effectively managed using a three-gene pyramid of Rag1+Rag2+Rag3. Additional Rag-genes have been discovered (Rag4 and Rag5), but whether the incorporation of these genes into novel three-gene pyramids will improve efficacy is not known. We tested single-gene (Rag1 and Rag2) and pyramid cultivars (Rag1+Rag2, Rag1+Rag2+Rag3, Rag1+Rag2+Rag4) to multiple biotypes in laboratory assays. Our results confirm that the Rag1+Rag2+Rag3 pyramid effectively manages all known A. glycines biotypes when compared with cultivars that are overcome by the associated biotype. Our results indicate that Rag1+Rag2+Rag4 would be an effective management option for biotype-1, biotype-2, and biotype-3 A. glycines, but had a negligible impact on biotype-4.

Loss of biodiversity and degradation of ecosystem services from agricultural lands remain important challenges in the United States despite decades of spending on natural resource management. To date, conservation investment has emphasized engineering practices or vegetative strategies centered on monocultural plantings of nonnative plants, largely excluding native species from cropland. In a catchment-scale experiment, we quantified the multiple effects of integrating strips of native prairie species amid corn and soybean crops, with prairie strips arranged to arrest run-off on slopes. Replacing 10% of cropland with prairie strips increased biodiversity and ecosystem services with minimal impacts on crop production. Compared with catchments containing only crops, integrating prairie strips into cropland led to greater catchment-level insect taxa richness (2.6-fold), pollinator abundance (3.5-fold), native bird species richness (2.1-fold), and abundance of bird species of greatest conservation need (2.1-fold). Use of prairie strips also reduced total water runoff from catchments by 37%, resulting in retention of 20 times more soil and 4.3 times more phosphorus. Corn and soybean yields for catchments with prairie strips decreased only by the amount of the area taken out of crop production. Social survey results indicated demand among both farming and nonfarming populations for the environmental outcomes produced by prairie strips. If federal and state policies were aligned to promote prairie strips, the practice would be applicable to 3.9 million ha of cropland in Iowa alone.

Cover crops are beneficial to agroecosystems because they decrease soil erosion and nutrient loss while increasing within-field plant diversity. Greater plant diversity within cropping systems can positively affect beneficial arthropod communities. We hypothesized that increasing plant diversity within annually rotated corn and soybean with the addition of a rye cover crop would positively affect the beneficial ground and canopy-dwelling communities compared with rotated corn and soybean grown without a cover crop. From 2011 through 2013, arthropod communities were measured at two locations in Iowa four times throughout each growing season. Pitfall traps were used to sample ground-dwelling arthropods within the corn and soybean plots and sweep nets were used to measure the beneficial arthropods in soybean canopies. Beneficial arthropods captured were identified to either class, order, or family. In both corn and soybean, community composition and total community activity density and abundance did not differ between plots that included the rye cover crop and plots without the rye cover crop. Most taxa did not significantly respond to the presence of the rye cover crop when analyzed individually, with the exceptions of Carabidae and Gryllidae sampled from soybean pitfall traps. Activity density of Carabidae was significantly greater in soybean plots that included a rye cover crop, while activity density of Gryllidae was significantly reduced in plots with the rye cover crop. Although a rye cover crop may be agronomically beneficial, there may be only limited effects on beneficial arthropods when added within an annual rotation of corn and soybean.

Background Plants are thought to produce ecdysteroids as a means of protection from insect herbivores. Some insects will not feed on plants containing high amounts of phytoecdysteroids, and this response could be limited to monophagous and oligophagous insects. The aim of this study was to determine whether phytoecdysteroids could inhibit feeding in several species of beetles that range from monophagous to polyphagous. Results Here we demonstrate that phytoecdysteroids, including 20-hydroxyecdysone, prevent several beetle species from feeding on preferred host plants, including the polyphagous Japanese beetle Popillia japonica (Scarabaeidae). Phytoecdysteroids prevented feeding damage when sprayed onto soybean plants in no-choice and choice assays in a dose-dependent manner. Laboratory assays indicate that other plants could be protected from Japanese beetle herbivory, including linden, wild grape, elm, Virginia creeper and rose leaves. Additional beetle species tested in the family Chrysomelidae included the oligophagous Cerotoma trifurcata and Diabrotica virgifera virgifera and the monophagous Trirhabda canadensis. All species were prevented from feeding when their preferred host plants were treated with phytoecdysteroids. Conclusion This study demonstrates that beetles, representing polyphagous and monophagous feeding guilds, can be prevented from feeding when phytoecdysteroids are applied to the leaf surface. The phytoecdysteroids could be utilized in pest management towards a variety of beetles, including the more pestiferous polyphagous species, if the compounds are placed on the leaf surface. © 2016 Society of Chemical Industry.

Background Soybean aphid, Aphis glycines, is an invasive insect in North America, considered one of the most important pests of soybean. Their management relies heavily on foliar insecticides, but there is growing effort to expand these tools to include aphid-resistant varieties. We explored if the LC50 and LC25 of lambda-cyhalothrin varied between virulent (resistant to Aphis glycines (Rag) soybeans) and avirulent (susceptible to Rag-genes soybeans) populations of soybean aphid with a leaf-dip bioassay. We also investigated the response to the LC25 of lambda-cyhalothrin on adults (F0) and their progeny (F1) for both avirulent and virulent soybean aphid. Results The LC50 of the virulent aphid population was significantly higher compared with the LC50 of the avirulent population. The LC25 significantly reduced fecundity of the F0 generation of avirulent soybean aphid, but no significant effect was observed for virulent aphids. In addition, the LC25 significantly shortened the adult pre-oviposition period (APOP) and lengthened the total pre-oviposition period (TPOP) of avirulent aphids, while the mean generation time (T) was significantly increased. For the virulent aphid, sublethal exposure significantly lengthened development time of first and third instars, TPOP, and adult longevity. In addition, all demographic parameters of virulent soybean aphid were significantly affected when they were exposed to the LC25 of lambda-cyhalothrin. Conclusion Our results demonstrate lambda-cyhalothrin is less toxic to virulent aphids and exposure to the LC25 can trigger hormesis, which may have implications for the long-term management of this pest with this insecticide as well as with aphid-resistant varieties of soybean. © 2019 Society of Chemical Industry.

Crop rotation alters agroecosystem diversity temporally, and increasing the number of crops in rotation schemes can increase crop yields and reduce reliance on pesticides. We hypothesized that increasing the number of crops in annual rotation schemes would positively affect ground-dwelling beneficial arthropod communities. During 2012 and 2013, pitfall traps were used to measure activity-density and diversity of ground-dwelling communities within three previously established, long-term crop rotation studies located in Wisconsin and Illinois. Rotation schemes sampled included continuous corn, a 2-yr annual rotation of corn and soybean, and a 3-yr annual rotation of corn, soybean, and wheat. Insects captured were identified to family, and non-insect arthropods were identified to class, order, or family, depending upon the taxa. Beneficial arthropods captured included natural enemies, granivores, and detritivores. The beneficial community from continuous corn plots was significantly more diverse compared with the community in the 2-yr rotation, whereas the community in the 3-yr rotation did not differ from either rotation scheme. The activity-density of the total community and any individual taxa did not differ among rotation schemes in either corn or soybean. Crop species within all three rotation schemes were annual crops, and are associated with agricultural practices that make infield habitat subject to anthropogenic disturbances and temporally unstable. Habitat instability and disturbance can limit the effectiveness and retention of beneficial arthropods, including natural enemies, granivores, and detritivores. Increasing non-crop and perennial species within landscapes in conjunction with more diverse rotation schemes may increase the effect of biological control of pests by natural enemies.

Western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), and northern corn rootworm, Diabrotica barberi Smith & Lawrence, are major pests of corn (Zea mays L.). Corn producing Bacillus thuringiensis (Bt) toxins are widely used to manage Diabrotica spp.; however, Bt resistance by D. v. virgifera has led to high levels of feeding injury in the field. We tested whether field history affected root injury and abundance of adult Diabrotica spp. In 2013 and 2014, four types of cornfields were sampled: 1) recently rotated fields, 2) continuous cornfields, 3) fields with a history of injury to Bt corn (past problem fields), and 4) fields with greater than one node of injury to Bt corn at the time of sampling (current problem fields). Data were collected on field history, root injury, and the abundance of adult Diabrotica spp. from each field. Root injury and the abundance of D. v. virgifera were significantly greater in current problem fields compared to the other field types, while D. barberi were significantly more abundant in recently rotated fields. Root injury and the abundance of D. v. virgifera did not differ among recently rotated fields, continuous cornfields, and past problem fields. Analysis of field history showed that recently rotated fields were characterized by significantly less Bt corn, soil-applied insecticides, and years planted to corn continuously. These results suggest that greater cropping practice diversity can reduce management inputs for Diabrotica spp.; however, its effects on resistance evolution remain undetermined.

Decreased pest pressure is sometimes associated with more diverse agroecosystems, including the addition of a rye cover crop (Secale cereale L.). However, not all pests respond similarly to greater vegetational diversity. Polyphagous pests, such as true armyworm (Mythimna unipuncta Haworth), black cutworm (Agrotis ipsilon Hufnagel), and common stalk borer (Papaipema nebris Guenee), whose host range includes rye have the potential to cause injury to crops following a rye cover crop. The objectives of this study were to compare the abundance of early-season insect pests and injury to corn (Zea mays L.) from fields with and without a rye cover crop on commercial farms. Fields were sampled weekly to quantify adult and larval pests and feeding injury to corn plants from mid-April until corn reached V8 stage, during 2014 and 2015. Measurements within fields were collected along transects that extended perpendicularly from field edges into the interior of cornfields. Adult true armyworm and adult black cutworm were captured around all cornfields, but most lepidopteran larvae captured within cornfields were true armyworm and common stalk borer. Cornfields with a rye cover crop had significantly greater abundance of true armyworm and greater proportion of injured corn. Both true armyworm abundance and feeding injury were significantly greater in the interior of cornfields with rye. Common stalk borer abundance did not differ between cornfields with or without rye cover. Farmers planting corn following a rye cover crop should be aware of the potential for increased presence of true armyworm and for greater injury to corn.

Multiple biotypes of soybean aphid, Aphis glycines, occur in North America adapted for survival (virulence) on soybean, Glycine max, with one or more different resistance to A. glycines (Rag) traits. The degree of genome-wide variance between biotypes and the basis of virulence remains unknown, but the latter is hypothesized to involve secreted effector proteins. Between 167,249 and 217,750 single nucleotide polymorphisms (SNPs) were predicted from whole genome re-sequencing of A. glycines avirulent biotype 1 (B1) and virulent B2, B3 and B4 colony-derived iso-female lines when compared to the draft B1 genome assembly, Ag_bt1_v6.0. Differences in nucleotide diversity indices (π) estimated within 1000 bp sliding windows demonstrated that 226 of 353 (64.0%) regions most differentiated between B1 and ≥ 2 virulent biotypes, representing 0.1% of the 308 Mb assembled genome size, are located on 15 unordered scaffolds. Furthermore, these 226 intervals were coincident and show a significant association with 326 of 508 SNPs with significant locus-by-locus F

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies., This work was supported through the National Socio-Environmental Synthesis Center (SESYNC) National Science Foundation Award DBI-1052875 for the project “Evidence and Decision-Support Tools for Controlling Agricultural Pests with Conservation Interventions” organized by D.S.K. and R.C.-K

The soybean aphid (Aphis glycines Hemiptera: Aphididae) is a major pest of soybean in the Midwest. An unmanaged aphid outbreak has the potential to reduce yield by up to 40 percent. During the summer, aphids rapidly reproduce, resulting in exponential population growth. Foliar-applied insecticides are the most widely used management strategy for protecting yield loss from soybean aphids. Using varieties carrying aphid resistance genes (i.e. Rag) also is an effective means to suppress aphids. However, virulent aphid biotypes can colonize resistant plants. Use of only aphid-resistant plants throughout a landscape could lead to the fixation of virulence in the soybean aphid population. Inclusion of an aphid-susceptible refuge can be an effective strategy to preserve the efficacy of Rag genes. Blended seed mixtures, or refuge-in-a-bag, is an approach used in corn, but is not yet available in soybean. A field experiment was conducted to test whether a refuge-in-a-bag approach can protect yield while maintaining a population of soybean aphids.

Soybean production in the north central United States has relied heavily on the use of foliar and seed applied insecticides to manage Aphis glycines (Hemiptera: Aphididae). An additional management strategy is the use soybean cultivars containing A. glycines resistance genes (Rag). Previous research has demonstrated that Rag cultivars are capable of preventing yield loss equivalent to the use of foliar and seed-applied insecticides. However, the presence of virulent biotypes in North America has raised concern for the durability of Rag genes. A resistance management program that includes a refuge for avirulent biotypes could limit the frequency at which virulent biotypes increase within North America. To what extent such a refuge reduces the effectiveness of aphid-resistant soybean is not clear. We conducted an experiment to determine whether a susceptible refuge mixed into resistant soybean (i.e., interspersed refuge or refuge-in-a-bag) affects the seasonal exposure of aphids, their natural enemies, biological control, and yield protection provided by aphid resistance. We compared three ratios of interspersed refuges (resistant: susceptible; 95:5, 90:10, 75:25) to plots grown with 100% susceptible or resistant soybean. We determined that an interspersed refuge of at least 25% susceptible seed would be necessary to effectively produce avirulent individuals. Interspersed refuges had negligible effects on yield and the natural enemy community. However, there was evidence that they increased the amount of biological control that occurred within a plot. We discuss the compatibility of interspersed refuges for A. glycines management and whether resistance management can prolong the durability of Rag genes.

Insect herbivores can increase the suitability of host plants for conspecifics by inducing susceptibility. Induced susceptibility can be separated into feeding facilitation, whereby herbivore feeding increases performance of conspecifics regardless of the genotype of the herbivore or plant, and obviation of resistance, whereby feeding by a virulent herbivore increases performance of avirulent conspecifics on resistant plants. Both forms occur between Aphis glycines (Hemiptera: Aphididae) and soybean. In natural and agricultural settings, A. glycines populations can colonize plants for brief periods before emigrating or being removed due to predation or insecticides. It is unclear if induced susceptibility lasts beyond the period when A. glycines are present on the plant. We measured the duration of induced susceptibility in the A. glycines-soybean system within a growth chamber by removing inducer populations after 24 h. We used an A. glycines-resistant soybean infested with an inducer population of either virulent, avirulent, or no aphids. Response populations of either virulent or avirulent aphids were added at three post-infestation times (24, 120, 216 h) and their densities measured 11 days after infestation. Feeding facilitation was lost within 24 h of the removal of avirulent inducer populations, and obviation of resistance diminished over time and was completely lost within 216 h of the removal of the virulent inducer populations. We discuss how these results support a hypothesis that virulence in A. glycines is due to effector proteins secreted by feeding aphids. We suggest that the duration of induced susceptibility may impact the durability of A. glycines resistance in soybean.

Insects trigger plants to release volatile compounds that mediate the interaction with both pest and beneficial insects. Soybean aphids (Aphis glycines) induces soybean (Glycine max) leaves to produce volatiles that attract predators of the aphid. In this research, we describe the use of solid-phase microextraction (SPME) for extraction of volatiles from A. glycines-infested plant. Objectives were to (1) determine if SPME can be used to collect soybean plant volatiles and to (2) use headspace SPME-GC-MS approach to screen compounds associated with A. glycines-infested soybeans, grown in the laboratory and in the field, to identify previously known and potentially novel chemical markers of infestation. A total of 62 plant volatiles were identified, representing 10 chemical classes. 39 compounds had not been found in previous studies of soybean volatile emissions. 3-hexen-1-ol, dimethyl nonatriene, indole, caryophyllene, benzaldehyde, linalool, methyl salicylate (MeSA), benzene ethanol, and farnesene were considered herbivore-induced plant volatiles (HIPVs). For reproductive field-grown soybeans, three compounds were emitted in greater abundance from leaves infested with A. glycines, cis-3-hexen-1-ol acetate, MeSA and farnesene. In summary, SPME can detect the emission of HIPVs from plants infested with insect herbivores.

Observations of virulent Aphis glycines Matsumura populations on resistant soybean in North America occurred prior to the commercial release of Rag genes. Laboratory assays confirmed the presence of four A. glycines biotypes in North America defined by their virulence to the Rag1 and Rag2 genes. Avirulent and virulent biotypes can co-occur and potentially interact on soybean, which may result in induced susceptibility. We conducted a series of experiments to determine if the survival of avirulent biotypes on susceptible and resistant soybean containing the Rag1 or Rag1 + Rag2 genes was affected by the presence of either avirulent or virulent conspecifics. Regardless of virulence to Rag genes, initial feeding by conspecifics increased the survival of subsequent A. glycines populations on both susceptible and resistant soybean. Avirulent populations increased at the same rate as virulent populations if the resistant plants were initially colonized with virulent aphids. These results are the first to demonstrate that virulent A. glycines increase the suitability of resistant soybean for avirulent conspecifics, thus explaining the lack of genetic differentiation observed in North America between A. glycines populations on resistant and susceptible soybean. These results suggest the occurrence of virulence toward Rag genes in North America may be overestimated. In addition this may alter the selection pressure for virulence genes to increase in a population. Therefore, insect resistance management models for A. glycines may need to incorporate induced susceptibility factors to determine the relative durability of resistance genes.

Soybean, Glycine max (L.) Merrill, flowers can be a source of nectar and pollen for honey bees, Apis mellifera L. (Hymenoptera: Apidae), wild social and solitary bees (Hymenoptera: Apoidea), and flower-visiting flies (Diptera). Our objectives were to describe the pollinator community in soybean fields, determine which sampling method is most appropriate for characterizing their abundance and diversity, and gain insight into which pollinator taxa may contact soybean pollen. We compared modified pan traps (i.e., bee bowls), yellow sticky traps, and sweep nets for trapping pollinators in Iowa soybean fields when soybeans were blooming (i.e., reproductive stages R1-R6) during 2011 and 2012. When all trap type captures were combined, we collected 5,368 individuals and at least 50 species. Per trap type, the most pollinators were captured in bee bowls (3,644 individuals, 44 species), yellow sticky traps (1,652 individuals, 32 species), and sweep nets (66 individuals, 10 species). The most abundant species collected include Agapostemon virescens F. and Lasioglossum (Dialictus) species (Hymenoptera: Halictidae), Melissodes bimaculata Lepeletier (Hymenoptera: Apidae), and Toxomerus marginatus Say (Diptera: Syrphidae). To determine if these pollinators were foraging on soybean flowers, we looked for soybean pollen on the most abundant bee species collected that had visible pollen loads. We found soybean pollen alone or intermixed with pollen grains from other plant species on 29 and 38% of the bees examined in 2011 and 2012, respectively. Our data suggest a diverse community of pollinators-composed of mostly native, solitary bees-visit soybean fields and forage on their flowers within Iowa.

The important questions about agriculture, climate, and sustainability have become increasingly complex and require a coordinated, multifaceted approach for developing new knowledge and understanding. A multistate, transdisciplinary project was begun in 2011 to study the potential for both mitigation and adaptation of corn-based cropping systems to climate variations. The team is measuring the baseline as well as change of the system's carbon (C), nitrogen (N), and water footprints, crop productivity, and pest pressure in response to existing and novel production practices. Nine states and 11 institutions are participating in the project, necessitating a well thought out approach to coordinating field data collection pro- cedures at 35 research sites. In addition, the collected data must be brought together in a way that can be stored and used by persons not originally involved in the data collection, necessi- tating robust procedures for linking metadata with the data and clearly delineated rules for use and publication of data from the overall project. In order to improve the ability to compare data across sites and begin to make inferences about soil and cropping system responses to cli- mate across the region, detailed research protocols were developed to standardize the types of measurements taken and the specific details such as depth, time, method, numbers of samples, and minimum data set required from each site. This process required significant time, debate, and commitment of all the investigators involved with field data collection and was also informed by the data needed to run the simulation models and life cycle analyses. Although individual research teams are collecting additional measurements beyond those stated in the standardized protocols, the written protocols are used by the team for the base measurements to be compared across the region. A centralized database was constructed to meet the needs of current researchers on this project as well as for future use for data synthesis and modeling for agricultural, ecosystem, and climate sciences.

Reconstructing prairie vegetation in row crop-dominated agricultural landscapes may contribute to several ecosystem services, including the biological control of insect pests, such as the soybean aphid Aphis glycines Matsumura. The influence of the amount and configuration of reconstructed prairie vegetation on the delivery of ecosystem services was investigated in several small catchments at Neal Smith National Wildlife Refuge in Iowa. Treatments include catchments entirely in row crops under a no-till, corn-soybean (Zea mays L.-Glycine max [L.] Merrill) rotation, catchments with 10% of the land in prairie located at the base, and catchments with 10 or 20% of the land in multiple contour strips of prairie. During 2009 and 2011 growing seasons, we measured abundance and diversity of aphidophagous insect predators in response to treatment and habitat type (i.e., soybean, prairie). In 2011, we further studied the biological control of soybean aphids by artificially infesting uncaged and caged plants to prevent exposure from predators. While aphidophagous predators were more abundant in prairie, populations of key aphid predators did not significantly differ among treatments. Biological control of the soybean aphid did not differ among treatments or with distance from prairie. Our results suggest that prairie strips, in addition to providing soil and water quality benefits, may increase the populations of beneficial insects, but may not directly impact biocontrol. We propose several hypotheses to explain why we did not observe more soybean aphid predation with the increased abundance of aphidophagous predators in catchments containing prairie.

Native plants attractive to beneficial insects may improve the value of buffer strips by increasing biodiversity and enhancing the delivery of insect-derived ecosystem services. In a 2-yr field experiment, we measured the response of insect communities across nine buffers that varied in plant diversity. We constructed buffers with plants commonly found in buffers of USDA-certified organic farms in Iowa (typically a single species), recommended for prairie reconstruction, or recommended for attracting beneficial insects. We hypothesized that the diversity and abundance of beneficial insects will be 1) greatest in buffers composed of diverse plant communities with continuous availability of floral resources, 2) intermediate in buffers with reduced species richness and availability of floral resources, and 3) lowest in buffers composed of a single species. We observed a significant positive relationship between the diversity and abundance of beneficial insects with plant community diversity and the number of flowers. More beneficial insects were collected in buffers composed of species selected for their attractiveness to beneficial insects than a community recommended for prairie restoration. These differences suggest 1) plant communities that dominate existing buffers are not optimal for attracting beneficial insects, 2) adding flowering perennial species could improve buffers as habitat for beneficial insects, 3) buffers can be optimized by intentionally combining the most attractive native species even at modest levels of plant diversity, and 4) plant communities recommended for prairie reconstruction may not contain the optimal species or density of the most attractive species necessary to support beneficial insects from multiple guilds.

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an invasive insect pest of soybean [Glycine max (L.) Merr. (Fabaceae)] in North America, and it has led to extensive insecticide use in northern soybean-growing regions there. Host plant resistance is one potential alternative strategy for managing soybean aphid. Several Rag genes that show antibiosis and antixenosis to soybean aphid have been recently identified in soybean, and field-testing and commercial release of resistant soybean lines have followed. In this article, we review results of field tests with soybean lines containing Rag genes in North America, then present results from a coordinated regional test across several field sites in the north-central USA, and finally discuss prospects for use of Rag genes to manage soybean aphids. Field tests conducted independently at multiple sites showed that soybean aphid populations peaked in late summer on lines with Rag1 or Rag2 and reached economically injurious levels on susceptible lines, whereas lines with a pyramid of Rag1 + Rag2 held soybean aphid populations below economic levels. In the regional test, aphid populations were generally suppressed by lines containing one of the Rag genes. Aphids reached putative economic levels on Rag1 lines for some site years, but yield loss was moderated, indicating that Rag1 may confer tolerance to soybean aphid in addition to antibiosis and antixenosis. Moreover, no yield penalty has been found for lines with Rag1, Rag2, or pyramids. Results suggest that use of aphid-resistant soybean lines with Rag genes may be viable for managing soybean aphids. However, virulent biotypes of soybean aphid were identified before release of aphid-resistant soybean, and thus a strategy for optimal deployment of aphid-resistant soybean is needed to ensure sustainability of this technology.

Natural enemies of the invasive pest Aphis glycines Matsumura can prevent its establishment and population growth. However, current A. glycines management practices include the application of broad-spectrum insecticides that affect pests and natural enemies that are present in the field at the time of application. An alternative is the use of selective insecticides that affect the targeted pest species, although having a reduced impact on the natural enemies. We tested the effects of esfenvalerate, spirotetramat, imidacloprid, and a combination of spirotetramat and imidacloprid on the natural enemies in soybean during the 2009 and 2010 field season. The natural enemy community that was tested differed significantly between 2009 and 2010 (F = 87.41; df = 1, 598; P0.0001). The most abundant natural enemy in 2009 was Harmonia axyridis (Pallas) (56.0%) and in 2010 was Orius insidiosus (Say) (41.0%). During 2009, the abundance of natural enemies did not vary between the broad-spectrum and selective insecticides; however, the abundance of natural enemies was reduced by all insecticide treatments when compared with the untreated control. In 2010, the selective insecticide imidacloprid had more natural enemies than the broad-spectrum insecticide. Although we did not observe a difference in the abundance of the total natural enemy community in 2009, we did observe more H. axyridis in plots treated with spirotetramat. In 2010, we observed more O. insidiosus in plots treated with imidacloprid. We suggest a couple of mechanisms to explain how the varying insecticides have different impacts on separate components of the natural enemy community.

Linolenic acid is a precursor to components in plant defense responses to pests and pathogens. Soybean cultivars with altered seed linolenic acid contents have been developed for improved oil qualities, specifically reduced fatty acid content with increased stability. We examined how three common soybean pests, the soybean cyst nematode (SCN, Heterodera glycines ), brown stem rot (BSR) caused by Cadophora gregata and the soybean aphid (SBA; Aphis glycines ), affect yield and seed linolenic acid percentage of low linolenic acid cultivars. In a micro-plot field experiment, soybean cultivars with varying concentrations of linolenic acid in the seed (ultra-low or low) and resistance to SCN (susceptible or resistant) were grown at a central Iowa research farm. Plots were kept free of pests (control) or artificially infested with a single pest (SCN, BSR or SBA) or the combination of all three pests (multiple pest). The use of resistant cultivars (SCN and BSR) or an insecticide at an economic threshold (SBA) was analyzed to determine the efficacy of current management recommendations for low linolenic acid soybean production. Seed was collected at the end of the season to measure yield and grain composition. All three pests alone or in combination were capable of reducing yield, but only the three pests in combination were capable of affecting seed linolenic acid percentages, increasing linolenic acid percentages by 11.7% in SCN-susceptible cultivars. For all three pests, current management recommendations (resistant cultivars or economic thresholds) provided protection of both yield and grain composition, indicating no changes in management are necessary for altered linolenic acid soybean cultivars.