Soybean Aphid Resistance Research Articles

Soybean aphid management and perception of insecticide resistance by farmers

Abstract In the Midwest United States, soybean aphids can cause significant economic losses in soybean production. The repeated use of insecticides within the same family has led to the development of insecticide resistance in soybean aphids. Implementing integrated pest management (IPM) and insecticide-resistance management (IRM) strategies can help farmers reduce the frequency of insecticide applications and delay the evolution of soybean aphid resistance while reducing production costs, maintaining yields, and protecting the environment. Farmers play a crucial role in implementing such practices; therefore, to understand farmers’ practices for management of soybean aphids and their perceptions of insecticide resistance, a survey of soybean farmers in Minnesota and North Dakota was conducted in 2021. Overall, the reported decision-making sources were similar for both farmers who changed and those who did not change their aphid management due to insecticide resistance; these were crop consultants and agricultural retailers. The threshold used by farmers in both groups to determine whether to use a foliar insecticide was lower than the research-based threshold for soybean aphids, and farmers were aware that this could contribute to insecticide resistance. In addition, farmers who changed soybean aphid management were more concerned than farmers who did not change about insecticide resistance and were implementing good practices such as scouting, using labeled application rates, and rotating insecticide modes of action. The results of this research can inform the refinement of IPM and IRM programs as well as extension education efforts.

Registration of 64 soybean germplasm lines with all combinations of five soybean aphid resistance genes in two genetic backgrounds

AbstractSoybean aphid is a serious pest in North America, and infestations can cause economically significant losses. Aphid resistance genes have been identified and mapped with genetic markers, and the deployment of cultivars with pyramids of these genes could offer durable resistance. There is a need, however, for soybean [Glycine max (L.) Merr.] lines with different gene pyramids to be developed and tested to improve our understanding of what combinations provide the most resistance across aphid biotypes. We backcrossed the resistance genes Rag1, Rag2, Rag3, Rag4, and Rag6 into the background of two soybean cultivars, and lines with all 32 combinations of these five genes were developed in each background. These lines, LD19‐APH01–LD19‐APH64 (Reg. no. GP‐459–GP‐522, PI 701410–PI 701473), were evaluated for agronomic traits in the field and lines from one background were evaluated for resistance to four soybean aphid biotypes. There were significant differences among the performance of the backcross lines for agronomic traits; however, yield performance for most of the backcross lines did not significantly differ from the recurrent parent. Those lines with the Rag6 resistance gene and many gene pyramids showed a high level of resistance to all four aphid biotypes. Because these lines have the resistance genes in a mostly uniform background, they will be a useful source of germplasm for researchers studying soybean aphid isolates and the interaction between resistance genes and aphid isolates, as well as for breeders who are developing germplasm with resistance gene pyramids.

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

BackgroundSoybean 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.ResultsAt 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.ConclusionThis 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.

Fine Mapping and Characterization of an Aphid-Resistance Gene in the Soybean Landrace Fangzheng Moshidou.

The soybean aphid poses a severe threat to soybean quality and yield by sucking phloem sap and transmitting plant viruses. An early-maturing and highly resistant soybean landrace, Fangzheng Moshidou, with markedly reduced aphid colonization has been identified by screening of aphid-resistant soybean accessions. In a population derived from the cross of Fangzheng Moshidou with the susceptible cultivar Beifeng 9, resistance was conferred by a single dominant gene. Three linked markers, Satt114, Satt334, and Sct_033, on chromosome 13 were identified by bulked-segregant analysis. Additional simple-sequence repeat and single-nucleotide polymorphism (SNP) markers were developed for gene mapping. The resistance of Fangzheng Moshidou was fine-mapped to the interval between the SNP markers YCSNP20 and YCSNP80, corresponding to 152.8 kb in the Williams 82 assembly 2 genome. This region was near the reported loci Rag2 and Rag5 but did not overlap the interval containing them. A unique haplotype is described for Fangzheng Moshidou that distinguishes it from soybean accessions PI 587972, PI 594879, and PI 567301B in the interval containing Rag2 and Rag5. These results indicate that Fangzheng Moshidou harbors a novel gene at a tightly linked resistance locus, designated as RagFMD. Fourteen candidate genes were annotated in the fine-mapping region, including seven NBS-LRR genes, which are usually considered resistance genes in plant defense. Most of these candidate genes showed variations distinguishing the resistant and susceptible parents and some genes also showed differences in expression between the two parental lines and at several times after aphid infestation. Isolation of RagFMD would advance the study of molecular mechanisms of soybean aphid resistance and contribute to precise selection of resistant soybeans.

Registration of seven disease‐ and pest‐resistant vegetable soybean germplasm lines

AbstractSoybean [Glycine max (L.) Merr.] germplasm lines LB18‐49 (Reg. no. GP‐448, PI 699118), LB18‐52 (Reg. no. GP‐456, PI 699119), LB18‐57 (Reg. no. GP‐455, PI 699120), LB18‐58 (Reg. no. GP‐454, PI 699487), LB18‐65 (Reg. no. GP‐453, PI 699488), LB18‐67 (Reg. no. GP‐452, PI 699489), and LB18‐75 (Reg. no. GP‐451, PI 699121) are large seeded, non‐genetically modified organism soybean lines ranging in maturity from maturity group (MG) 00 through MG IV. Each line contains a single gene for resistance to soybean aphid or Phytophthora root and stem rot (PRSR). LB18‐49 and LB18‐58 have resistance to soybean aphid biotype 3 (Rag1) provided by LD06‐16721. Soybean aphid resistance to biotype 2 (Rag2) was derived from LD08‐12441 for LB18‐65. LD08‐12582 provided Rag2 resistance for LB18‐52 and LB18‐57. ‘Williams 82’ was the source of the PRSR resistance gene, Rps1k, for LB18‐67 and LB18‐75. Large‐seeded cultivars ‘Tohya’ (MG 00), ‘BeSweet 2001’ (MG II), ‘Gardensoy 24’ (MG II), and ‘Gardensoy 41’ (MG IV) served as recurrent parents with pest‐resistant donor lines to develop large‐seeded, pest‐resistant soybean lines in a range of maturity groups. The combined pest resistance and large seed size, in a range of maturities, will be valuable for breeders developing large‐seeded pest‐resistant cultivars.

Investigation of Metabolic Resistance to Soybean Aphid (Aphis glycines Matsumura) Feeding in Soybean Cultivars.

Simple SummaryThis project examined the interaction between soybean aphids and Ontario-grown soybean cultivars to determine which leaf metabolites were most associated with aphid resistance. Tolerance and resistance were determined by measuring the growth and reproduction of aphids and leaf feeding damage over 10-day and 4-week infestation periods. Chromatographic techniques were used for the analysis of legume-specific plant natural products and isoflavonoids, and high-resolution mass spectrometry was used for the identification of free amino acids in aphid-resistant, tolerant, and susceptible soybean cultivars. There was a low correlation between isoflavonoid leaf concentrations and aphid resistance in the soybean varieties studied; however, the aphid-resistant cultivars were determined to have lower free amino acid concentrations, indicating that lower nutrient quality could be responsible for the resistance observed. Identifying these cultivars is important for managing aphid populations and provides an additional tool for soybean integrated pest management.Soybean aphid (Aphis glycines) is a major soybean (Glycine max) herbivore pest in many soybean growing regions. High numbers of aphids on soybean can cause severe reductions in yield. The management of soybean aphids includes monitoring, insecticide applications when required, and the use of resistant cultivars. Soybean aphid-resistant soybean varieties are associated with genes that confer one or more categories of resistance to soybean aphids, including antibiosis (affects survival, growth, and fecundity), antixenosis (affects behaviour such as feeding), and tolerance (plant can withstand greater damage without economic loss). The genetic resistance of soybean to several herbivores has been associated with isoflavonoid phytoalexins; however, this correlation has not been observed in soybean varieties commonly grown in southern Ontario, Canada. Isoflavonoids in the leaves of 18 cultivars in the early growth stage were analyzed by HPLC and the concentration by fresh weight was used to rate the potential resistance to aphids. Greenhouse and growth cabinet trials determined that the cultivars with greater resistance to aphids were Harosoy 63 and OAC Avatar. The most susceptible cultivar was Maple Arrow, whereas Pagoda and Conrad were more tolerant to aphid feeding damage. Overall, there was a low correlation between the number of aphids per leaf, feeding damage, and leaf isoflavonoid levels. Metabolite profiling by high-resolution LC-MS determined that the most resistant cultivar had on average lower levels of certain free amino acids (Met, Tyr, and His) relative to the most susceptible cultivar. This suggests that within the tested cultivars, nutritional quality stimulates aphid feeding more than isoflavonoids negatively affect aphid feeding or growth. These findings provide a better understanding of soybean host plant resistance and suggest ways to improve soybean resistance to aphid feeding through the breeding or metabolic engineering of leaf metabolites.

Exploring the Dynamics of Virulent and Avirulent Aphids: A Case for a 'Within Plant' Refuge.

The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is an invasive pest that can cause severe yield loss to soybeans in the North Central United States. A tactic to counter this pest is the use of aphid-resistant soybean varieties. However, the frequency of virulent biotypes that can survive on resistant varieties is expected to increase as more farmers use these varieties. 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 nonlocal, differential equation population model to explore the dynamics of these biological mechanisms on soybean plants coinfested with virulent and avirulent aphids. We then use demographic parameters from laboratory experiments to perform numerical simulations via the model. We used this model to determine that initial conditions are an important factor in the season-long cooccurrence of both biotypes. The initial population of both biotypes above the resistance threshold or avirulent aphid close to resistance threshold and high virulent aphid population results in coexistence of the aphids throughout the season. These simulations successfully mimicked aphid dynamics observed in the field- and laboratory-based microcosms. The model showed an increase in colonization of virulent aphids increases the likelihood that aphid resistance is suppressed, subsequently increasing the survival of avirulent aphids. This interaction produced 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.

Challenges and Prospects of Wild Soybean as a Resistance Source Against Soybean Aphid (Hemiptera: Aphididae)

AbstractCrop wild relatives (CWRs) have high levels of genetic diversity compared to their domesticated descendants. Soybean (Glycine max) has over 20 species of CWRs, most of which are in secondary and tertiary gene pools. Glycine soja, hereafter ‘soja,’ is the only wild relative in the primary gene pool, i.e., species that readily cross with soybean. Soja has many advantageous traits that may be transferrable to soybean, including resistance to insect pests, with particularly strong sources of resistance to the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae). Soybean aphid has been a major soybean pest in the United States and Canada since 2000 and a longstanding pest in East Asia. This paper reviews the challenges of developing soybean with durable resistance to soybean aphid in light of multiple, virulent biotypes in North America and China. It also examines particular challenges in evaluating soja germplasm for soybean aphid resistance and resultant solutions to those challenges. Soja germplasm is widely available, but from our experience, the logistics associated with reliably procuring high-quality soja seed has posed the main challenge in working with this CWR. This review highlights soja accessions identified with strong resistance to soybean aphid and their genetic bases, and it discusses possible strategies for exploiting aphid-resistant soja accessions to improve soybean pest management.

Variation in Soybean Aphid (Hemiptera: Aphididae) Biotypes Within Fields.

Soybean aphid (Aphis glycines Matsumura (Hemiptera: Aphididae)) has been a major pest of soybean in North America since its detection in this continent in 2000 and subsequent spread. Although several aphid resistance genes have been identified, at least four soybean aphid biotypes have been discovered, with three of them being virulent on soybean cultivars with certain soybean aphid resistance genes. These biotypes are known to vary across years and locations, but information on their variation within single fields is limited. An investigation was conducted to study the variation of soybean aphid biotypes within single townships and fields in Minnesota. Screening of 28 soybean aphid isolates collected from seven soybean fields (six soybean fields in Cairo and Wellington Townships of Renville County, MN and one field in Wilmar Township of Kandiyohi County, MN) revealed the existence of multiple known biotypes of soybean aphid within single fields of soybean. We found up to three biotypes of soybean aphid in a single field. Two biotypes were found in five fields while only one field had only a single biotype. Three isolates presented reactions on a panel of resistant and susceptible indicator lines that were different from known biotypes. These results highlight the importance of characterizing soybean aphid biotypes in small geographical areas and utilizing generated knowledge to develop soybean cultivars pyramided with multiple resistance genes. The outcome will be decreased use of insecticides, thereby improving economic and environmental sustainability of soybean production.

Soybean aphid infestation and crop yield in relation to cultivar, foliar insecticide, and insecticidal seed treatment in South Dakota

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), remains an important pest of soybean, Glycine max (L.) Merr., in areas of the Midwestern United States and southern Canada. Options for managing soybean aphid are currently limited to insecticides and aphid-resistant varieties. Farmers commonly employ a prophylactic treatment of soybean seed with a neonicotinoid insecticide such as thiamethoxam and often a remedial, late-season application of foliar insecticides such as the pyrethroid, λ-cyhalothrin. Environmental concerns about detrimental side effects of neonicotinoids and the substantiation of pyrethroid resistance in field populations of soybean aphid have strengthened the case for planting aphid-resistant soybean cultivars. We conducted a three-year field study in eastern South Dakota, United States, that evaluated commercially-available active substances and enhanced plant materials for soybean aphid management that included a thiamethoxam seed treatment, spray application of λ-cyhalothrin, and an aphid-resistant soybean cultivar containing a pyramid of the Rag1 and Rag2 aphid-resistance genes. Soybean aphid infestations had sustained, economically injurious levels in 2015, but not the other two years. The three management tactics independently reduced soybean aphid population densities. Thiamethoxam and the resistant cultivar suppressed cumulative aphid-days (CAD) in all three years, whereas the λ-cyhalothrin spray decreased CAD in 2015 and 2017. By far, the resistant cultivar had the greatest impact on soybean aphid populations, reducing CAD by 28- to 150-fold year−1, with mean numbers of aphids much less than 100 soybean aphids plant−1. Thiamethoxam seed treatment reduced CAD by 1.7- to 3.5-fold year−1, and λ-cyhalothrin reduced it from 2.0- to 5.6-fold year−1. Soybean yield was not affected by treatments in 2015. Yield was greater for the susceptible than for the resistant cultivar in 2016, and yield was greater for plots without foliar insecticide in 2017. Implications for the use of these management tactics against soybean aphid are discussed.

Aphid resistance is the future for soybean production, and has been since 2004: efforts towards a wider use of host plant resistance in soybean.

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.

Jasmonic Acid-Isoleucine (JA-Ile) Is Involved in the Host-Plant Resistance Mechanism Against the Soybean Aphid (Hemiptera: Aphididae).

Host-plant resistance (HPR) is an important tool for pest management, affording both economic and environmental benefits. The mechanisms of aphid resistance in soybean are not well understood, but likely involve the induction of the jasmonic acid (JA) pathway, and possibly other phytohormone signals involved in plant defense responses. Despite the efficacy of aphid resistance in soybean, virulent aphids have overcome this resistance through mostly unknown mechanisms. Here, we have used metabolomic tools to define the role of plant phytohormones, especially the JA pathway, in regulating interactions between aphid-resistant soybean and virulent aphids. We hypothesized that virulent aphids avoid or suppress the JA pathway to overcome aphid resistance. Our results suggested that aphid-resistant soybean increased accumulation of JA-isoleucine (JA-Ile) only when infested with avirulent aphids; virulent aphids did not cause induction of JA-Ile. Further, applying JA-Ile to aphid-resistant soybean reduced subsequent virulent aphid populations. The concentrations of other phytohormones remained unchanged due to aphid feeding, highlighting the importance of JA-Ile in this interaction. These results increase our knowledge of soybean resistance mechanisms against soybean aphids and contribute to our understanding of aphid virulence mechanisms, which will in turn promote the durability of HPR.

Resistance among selected wild soybean and associated soybean accessions against two virulent colonies of Aphis glycines (Hemiptera: Aphididae)

The soybean aphid (Aphis glycines) is an important pest of soybean (Glycine max). Wild soybean (Glycine soja; also known as ‘soja’) has many useful traits, including some accessions with aphid resistance that may be incorporated into modern soybean cultivars. The objective of this work was to evaluate 76 selected soja accessions and 14 associated soybean accessions for resistance against two virulent colonies of soybean aphid in environmental-chamber experiments. In free-choice tests, soja accessions PI 407175, PI 407190, PI 407206, PI 407240, PI 507624 and PI 562558 were resistant against the Accrue colony, and PI 407191wf and PI 597458 C were resistant against the Volga16 colony. None of the soybean test accessions except the resistant check, PI 437696, showed resistance against either colony in free-choice tests. In no-choice tests, soja accession PI 507624 showed strong resistance against the Accrue colony; whereas PI 407240 and PI 407190 had intermediate aphid levels; PI 597458 C showed strong resistance to Volga16 aphids, and PI 407191wf had an intermediate level of resistance. Based on results from both sets of tests, soja accessions PI 507624 and PI 597458 C may be strong candidates in breeding programs to develop aphid-resistant soybean cultivars.

The Resistant Soybean-Aphis glycines Interaction: Current Knowledge and Prospects

Soybean aphids (Aphis glycines Matsumura) are invasive insect pests of soybean, and they cause significant yield losses. Resistance to soybean aphids is conferred by Resistance to Aphis glycines (Rag) genes. Since the first discovery of aphid-resistant soybean genotypes in 2004, several studies have attempted to characterize Rag genes from aphid-resistant soybean genotypes. To date, 12 Rag genes and four quantitative trait loci for aphid resistance have been reported on soybean chromosomes 07, 08, 13, 16, and 17. Although candidate genes have been proposed for several discovered Rag loci, additional studies are needed to pinpoint, validate, and further explain the potential mechanisms of Rag gene action. A major challenge to utilizing host plant resistance is the discovery of virulent aphid biotypes that can colonize aphid-resistant soybean. This occurrence suggests the need for additional studies to devise strategies to enhance the effectiveness of aphid-resistant soybean. In this mini review, we discuss current knowledge on the resistant soybean-Aphis glycines interaction, potential mechanisms of Rag gene action, opportunities to discover new Rag genes, and prospects for utilization of host plant resistance to manage soybean aphids. A clearer understanding of host plant resistance to soybean aphids will guide researchers on strategies for developing soybean varieties with more durable aphid resistance, reducing the present challenge of virulent aphid biotypes.

Effects of aphid-resistant soybean on nontarget herbivores in Minnesota

The use of aphid-resistant soybean varieties containing Rag genes can provide an effective pest management strategy against soybean aphid (Aphis glycines Matsumura). However, the compatibility between soybean containing Rag genes and the management of other potential soybean pests (i.e., nontarget herbivores) is poorly understood. Therefore, our goal was to (1) assess the efficacy of pyramided (Rag1+Rag2) aphid-resistant soybean for reduction of soybean aphid populations, and (2) determine if aphid-resistant soybean affects populations of nontarget herbivores under field conditions. To accomplish these goals, field experiments were conducted in southeast Minnesota from 2015 to 2017 for a total of five site-years using whole-plant counts to assess soybean aphid densities and sweep-net sampling to estimate nontarget herbivore densities in plots of near-isoline soybean with Rag1+Rag2 (i.e., resistant) or no Rag genes (i.e., susceptible). Plant genotype (i.e., resistant or susceptible) affected seasonal abundance of soybean aphid, with fewer soybean aphids on aphid-resistant than susceptible soybean. Furthermore, plant genotype affected seasonal abundance of bean leaf beetle (Cerotoma trifurcata Forster), green cloverworm (Hypena scabra Fabricius), and potato leafhopper (Empoasca fabae Harris). Aphid-resistant soybean was associated with increased seasonal abundance of bean leaf beetle and reduced seasonal abundance of potato leafhopper and green cloverworm. The abundance of these herbivores was also associated with seasonal abundance of soybean aphid as a covariate. Results presented here confirm the efficacy of aphid-resistant soybean with Rag1+Rag2 against soybean aphid and show that aphid-resistant soybean can influence the seasonal abundance of nontarget herbivores in soybean. However, the magnitude of impacts of aphid-resistant soybean on nontarget herbivores was relatively small and likely of little-to-no agronomic significance, which suggests compatibility of aphid-resistant soybean with management of other potential pests.

Genetic mapping of soybean aphid biotype 3 and 4 resistance in PI 606390A

The soybean aphid (Aphis glycines Matsumura) is a pest of soybean (Glycine max (L.) Merr.) in many soybean-growing countries of the world, mainly in Asia and North America. While numerous aphid-resistance loci have been mapped, new and virulent aphid biotypes continue to be identified. PI 606390A confers resistance to all four characterized soybean aphid biotypes. The objectives of this study were to identify single nucleotide polymorphism (SNP) markers closely linked to the loci conferring resistance to soybean aphid biotypes 3 and 4. One hundred and eight F6:7 families from a cross between the susceptible experimental line HR09-018 and the resistant PI 606390A plus the two parental lines were screened with aphid biotypes 3 and 4 using greenhouse choice tests. Broad-sense heritability estimates ranged from 0.69 to 0.91. Correlation between biotype 3 and biotype 4 resistance was also moderate (45–55%). A total of 1847 SNP markers were mapped to 22 linkage groups, and loci for resistance to both aphid biotypes were mapped to a 14 cM region on chromosome 18 using composite interval mapping. The locus explained between 26 and 40% of the phenotypic variation suggests the presence of a major locus and additional unidentified minor quantitative trait loci (QTL). A new symbol qRag-G is proposed to designate this new locus that will be useful for the development of durable aphid-resistant soybean cultivars.

Identification and Genetic Characterization of Soybean Accessions Exhibiting Antibiosis and Antixenosis Resistance to Aphis glycines (Hemiptera: Aphididae).

Cultivation of aphid-resistant soybean varieties can reduce yield losses caused by soybean aphids. However, discovery of aphid biotypes that are virulent on resistant soybean greatly threatens sustained utilization of host plant resistance to control soybean aphids. The objective of this study was to identify and genetically characterize aphid resistant soybean accessions in a diverse collection of 308 plant introductions in maturity groups (MG) I and II. In large-scale screening experiments conducted in the greenhouse, we identified 12 soybean accessions (10 aphid-resistant and 2 moderately resistant), including nine previously not reported for resistance against soybean aphids. Three accessions (PI 578374, PI 612759C, and PI 603546A) and the Rag3 resistant check (PI 567543C) were susceptible when infested with a high initial aphid level but resistant when infested with a low initial aphid level, a phenomenon termed as density-dependent aphid resistance. Six accessions (PI 054854, PI 378663, PI 578374, PI 612759C, PI 540739, and PI 603546A) conferred antibiosis, five (PI 438031, PI 603337A, PI 612711B, PI 437950, and PI 096162) conferred both antibiosis and antixenosis, while one (PI 417513B) had neither when tested in no-choice and pairwise choice experiments. Molecular genotyping of the 12 accessions using single-nucleotide polymorphism (SNP) markers linked to known aphid resistance (Rag) genes revealed that PI 578374 and PI 540739 did not have any tested marker variants and could potentially carry unreported Rag genes. Genome-wide association analyses for MG I accessions identified genomic regions associated with aphid resistance on chromosomes 10 and 12 for each level of initial aphid colonization.

Genome-Wide Association Mapping of Host-Plant Resistance to Soybean Aphid.

Soybean aphid [ Matsumura (Hemiptera: Aphididae)] is the most damaging insect pest of soybean [ (L.) Merr.] in the Upper Midwest of the United States and is primarily controlled by insecticides. Soybean aphid resistance (i.e., genes) has been documented in some soybean accessions but more sources of resistance are needed. Incorporation of the resistance into marketed varieties has also been slow. Genome-wide association mapping can aid in identifying resistant accessions by correlating phenotypic data with single nucleotide polymorphisms (SNPs) across a genome. Aphid population measures from 2366 soybean accessions were collected from published studies screening cultivated soybean () and wild soybean ( Siebold & Zucc.) with aphids exhibiting Biotype 1, 2, or 3 characteristics. Genotypic data were obtained from the SoySNP50K high-density genotyping array previously used to genotype the USDA Soybean Germplasm Collection. Significant associations between SNPs and soybean aphid counts were found on 18 of the 20 soybean chromosomes. Significant SNPs were found on chromosomes 7, 8, 13, and 16 with known genes. SNPs were also significant on chromosomes 1, 2, 4 to 6, 9 to 12, 14, and 17 to 20 where genes have not yet been mapped, suggesting that many genes remain to be discovered. These SNPs can be used to determine accessions that are likely to have novel aphid resistance traits of value for breeding programs.

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.

Evaluation of Insect Pests on Edamame Varieties in Minnesota.

Edamame, Glycine max (L.) Merrill, consumption continues to rise in the United States. Improved understanding of production threats, including insect pests, could facilitate increasing production of edamame in the north-central United States. Two years of complimentary field and laboratory experiments were performed to assess insect pest populations on commercially available edamame varieties. Fourteen varieties of edamame and four grain-type soybean varieties were tested in the laboratory with soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), and subsets of these varieties were tested in the field with naturally occurring insect populations. In the laboratory, mean aphid densities on the edamame varieties Agate and Chiba Green did not differ from the aphid-resistant grain-type soybean. Among edamame, aphid densities on Agate, Chiba Green, and Kuroshinju were significantly lower than on Hokkaido Black. In both years of the field experiment, aphid densities were significantly lower on the aphid-resistant grain-type compared to all others varieties. In 2016, aphid populations on edamame varieties did not differ from the aphid-susceptible grain-types. However, in 2017 with greater aphid exposure, differences were seen among edamame varieties, and between edamame and aphid-susceptible grain-types. In both years, potato leafhopper, Empoasca fabae (Harris) (Hemiptera: Cicadellidae), densities tended to be higher on edamame varieties compared to grain-types, and varied significantly among edamame varieties. In a laboratory study, differences were seen among varieties in mean density of trichomes, with grain-types generally having more trichomes than edamame. Results of this research will provide a foundation for development of production recommendations for edamame in the north-central United States.