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Crop 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.

Students of speciation debate the role of performance trade-offs across different environments early in speciation. We tested for early performance trade-offs with a host shift experiment using a member of the

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.

Simple Summary Slugs have become more frequent pests of field crops, including soybean. Monitoring slugs during the day is difficult because slugs are nocturnal, so trapping is often used to monitor populations. A variety of traps have been developed, though there are few direct comparisons of the different trap types. The objective of this study was to compare trapping efficiency of two types of slug refuge traps in soybeans. We tested a traditional shingle trap and a modified shingle trap with a water-filled pitfall trap beneath it. The modified shingle traps captured significantly more slugs than the traditional shingle trap, mainly due to the pitfall component (which was significantly cooler than the shingle component). As slug density decreased, this trend was most pronounced, suggesting that the modified shingle trap is a more sensitive sampling tool which may be useful in agronomic slug research. Abstract As more farmers adopt no- or reduced-tillage and/or cover crop land management practices, slugs have become more frequent pests of field crops, including soybean. Monitoring slugs visually is difficult because they are nocturnal, so several trapping methods have been developed, though comparisons of trap types are rare. The objective of this study was to compare trapping efficiency of two types of slug refuge traps in reduced-tillage soybeans following cover crop termination. We tested a traditional shingle trap and a modified shingle trap with a water-filled pitfall trap beneath it. Traps were deployed in 24 pairs in 2018 and 2019 in experimental soybean plots. We counted slug captures weekly over a 5-week time period each year. In 2018, we counted the total number of slugs under each trap type. In 2019, counts were categorized into specific trap components (shingle vs. in/on/under the pitfall). Temperature was also recorded in 2019. The modified shingle traps captured significantly more slugs than the traditional shingle traps, mainly due to the pitfall component. This trend was most pronounced as slug density decreased, suggesting that the modified shingle trap is a more sensitive sampling tool which may be particularly valuable when used for research purposes.

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.

The western bean cutworm (WBC), Striacosta albicosta (Lepidoptera: Noctuidae), can be a severe pest of transgenic corn in the western Plains and Great Lakes regions of North America, including on hybrids expressing the Bacillus thuringiensis (Bt) Cry1F toxin. The level and geographic distribution of Cry1F resistance are not completely known. Neonate S. albicosta from 10 locations between Nebraska and New York state were subjected to dose–response trypsin-activated native Cry1F toxin overlay bioassays. In 2017, the mean estimated lethal concentration causing 50% larval mortality (LC50) ranged from 15.1 to 18.4 µg Cry1F cm−2, and were not significantly different among locations. In 2018, LC50 estimates at Scottsbluff, NE (22.0 µg Cry1F cm−2) and Watertown, NY (21.7 µg Cry1F cm−2) were significantly higher when compared to locations in Michigan (15.8 µg Cry1F cm−2). Significantly lower 14-day larval weight among survivors was correlated with higher Cry1F dose. Results from this study indicate that S. albicosta survivorship on purified Bt Cry1F toxin shows a relatively even distribution across the native and range expansion areas where seasonal field infestations typically occur.

The soybean aphid (Aphis glycines Matsumura) is a major pest of soybean (Glycine max (L.) Merr.) in eastern Asia and in North America. Aphid-resistant soybean cultivars have been developed as a non-chemical management tactic, but viability of this tactic may depend on the availability of diverse resistance sources, including wild soybean (Glycine soja Siebold and Zucc.), in order to counter various resistance-breaking soybean aphid biotypes. In this study, 10 wild soybean accessions were identified as resistant in free-choice screening assays against avirulent soybean aphid biotype 1, and eight of the accessions were advanced for follow-up in two, 20-day-long no-choice assays. Two accessions, PI 65549 and PI 135624, did not differ from resistant check PI 549046 in number of aphids per plant after 10 and 20 days of infestation; accessions 99PI101404B, PI 549035 B, and PI 342618 A had more aphids than PI 549046 by day 20, but fewer aphids than known susceptible accessions. In a second no-choice assay, accessions 99PI81762 and PI 101404 A had fewer aphids than other test accessions but more aphids than PI 549046 by day 20. Because of particularly strong resistance in PI 135624 and PI 65549, these two accessions should be genetically characterized and tested for resistance against virulent soybean aphid biotypes.

Neonicotinoids alone and in combination with pyrethroid insecticides are common in crop production and suppress target herbivores effectively. The goal of this research was to quantify the effects of these insecticides on primary and secondary pests of soybeans and their natural enemies. We examined the effects of neonicotinoids alone applied to soybean seeds (thiamethoxam), neonicotinoids and pyrethroids applied to leaves (imidacloprid + β-cyfluthrin), and a combination of these treatments on arthropod abundance in soybean fields at two locations over two years in eastern South Dakota. Foliar applications of the insecticides suppressed soybean aphids, Aphis glycines Matsumara (Hemiptera: Aphididae), while thrips, (Thysanoptera: Thripidae) increased in numbers following exposure to the neonicotinoid insecticides alone or in combination with the pyrethroid in one of the locations and were significantly correlated with their major predators. Spider mites (Tetranychus urticae Koch) were not significantly affected by treatments. We also noted suppression of several taxa of predators following exposure to the insecticides. While low abundance of arthropods in the first year of the study limits our inferences, we conclude that both insecticide classes effectively suppress the key pest of soybean, soybean aphids, while their impact on secondary pests and on predators is variable. This research provides important contribution to our understanding of target and non-target impacts of insecticides commonly used in crop protection.

The soybean aphid (SA), Aphis glycines Matsumura, is a major pest of soybean in the north-central United States and south-central Canada. It is controlled primarily with insecticides, but the development of aphid-resistant soybean cultivars may provide an alternative management tactic. The viability of this management tactic depends on a diverse set of resistance sources in order to counter various resistance-breaking biotypes of SA, and the identification of new sources of resistance necessitates additional testing of soybean germplasm. The current study used no-choice tests to identify SA resistance in seven early maturing (maturity group I) soybean plant introductions (PIs) that had been advanced from free-choice screening trials. The tests showed PI 437353 and PI 612759 C had an intermediate level of resistance against avirulent SA, whereas PI 437282, PI 437658, PI 437733, PI 548417, and PI 548530 exhibited no significant resistance. Additional research is needed to determine if the source of resistance in PI 437353 and PI 612759 C is due to novel resistant genes, which would help diversify resistance to SA in soybean. Screening and follow-up tests of additional soybean germplasm is warranted in order to ensure the development of durable, SA-resistant cultivars.

Soybean aphid (Aphis glycines Matsumura) is a pest of soybean [Glycine max (L.) Merr] in the Midwestern U.S. and southern Canada. Host plant resistance provides an alternative to insecticides for soybean aphid management. Soybean with Rag1 + Rag2 aphid resistance is available commercially but does not protect against soybean aphid biotype 4 colonization. To find sources of resistance to soybean aphid biotype 4, we turned to soybean’s progenitor Glycine soja (Sieb. and Zucc.). Twenty soja plant introductions (PIs) with previously identified resistance to avirulent soybean aphid biotype 1 were assessed in free-choice tests against biotype 4, followed by a no-choice test for promising PIs. Experiments were repeated using three soybean aphid biotype 4 colonies, collected from separate site-years (Lomira, WI 2013; Volga, SD 2015, 2016). Free-choice tests identified six, three, and eight soja PIs with putative resistance to Lomira13, Volga15, and Volga16 aphid colonies, respectively. No-choice tests identified six, two, and six soja PIs that continued to suppress Lomira13, Volga15, and Volga16 aphids, respectively. PI 65549 and PI 101404A were resistant to each of the three colonies of soybean aphid biotype 4 and may contribute to durable resistance against soybean aphid.

Soybean, Glycine max (L.) Merr., has been grown as a forage and as an important protein and oil crop for thousands of years. Domestication, breeding improvements and enhanced cropping systems have made soybeans the most cultivated and utilized oilseed crop globally. Soybeans provide a high-quality protein source for livestock and aquaculture, oil for industrial uses and a valued component of human diets. Originating in China and Eastern Asia, today 80–85% of the world’s soybeans, approximately 88 million ha, are grown in the Western Hemisphere. United States soybean breeding and development efforts for over 80 years have transitioned from primarily universities and United States Department of Agriculture (USDA) programs to private company-led investments in commercial cultivar development. Soybean breeders continuously adapt tools and technologies that encompass classical breeding, mutation breeding and marker-assisted selection, biotechnology and transgenic approaches, gene silencing, and genome editing. In addition to breeding technologies, improved agronomics, precision agriculture and digital agriculture have advanced soybean production and profitability. The primary goals of soybean breeding and cropping systems advances include yield improvement, increased seed protein and oil composition and quality, and yield preservation through weed, pathogen, insect pest and abiotic stress resistance and management. This chapter primarily describes the introduction and improvement of soybeans in the United States. Contributing authors describe classical and molecular breeding, biotechnology, biotic and abiotic stress management, and soybean agronomics and cropping systems improvements that maximize soybean productivity, profitability and sustainability to supply a continually increasing world demand for protein and oil for feed, fuel and food.

Soybean aphid, Aphis glycines Matsumura, remains the key insect pest of soybean, Glycine max (L.) Merrill, in the north-central United States. Management of this pest has relied primarily on scouting and application of foliar insecticides based on an economic threshold (ET) of 250 aphids per plant. This review explains why this ET remains valid for soybean aphid management, despite changes in crop value and input costs. In particular, we review how soybean aphid impacts soybean yield, the role of biology and economics in recommendations for soybean aphid management, and the short- and long-term consequences of inappropriately timed insecticide applications. Accepted for publication 13 December 2016.

Since the discovery of the invasive soybean aphid, Aphis glycines Matsumura, in the USA in 2000, populations have expanded throughout the Midwestern USA and Canada. Its negative economic impact on soybean [Glycine max (L.) Merr.] yield provides the impetus to continue investigating the effectiveness of host plant resistance which has been affected by soybean aphid biotypes that overcome soybean plants containing Rag (resistance to A. glycines) genes. In this study, 14 aphid clones collected on soybean and buckthorn (Rhamnus cathartica L.) plants along with four known aphid biotypes (from our stock collection) were evaluated in no-choice assays by quantifying the number of aphids on soybean genotypes with Rag genes and the susceptible cultivar Williams 82. No-choice assays were conducted using detached leaves and whole plants. Inconsistent responses of the biotypes from the stock collection by using detached leaves confirm the efficacy of whole plant assays to accurately differentiate biotypes. None of the biotypes or field clones from Illinois, Indiana and South Dakota overcame the resistance of soybean genotypes LD14-8004 (Rag1) and PI437696. A soybean aphid clone from Wooster, Ohio readily colonized LD14-8002 (Rag2), but did not overcome any of the other resistance genes indicating that it is different from biotypes 3 and 4, which also overcome LD14-8002 (Rag2) and, respectively, LD14-8004 (Rag1) and LD14-8006 (Rag3).

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), infestations of soybean, Glycine max (L.) Merr. (Fabales: Fabaceae), and the associated yield loss have led to a large dependence on insecticidal management in soybean throughout the Midwestern United States. However, several populations of pyrethroid-resistant soybean aphids have recently been found in Iowa, Minnesota, North Dakota and South Dakota, which highlights the importance of alternative management approaches. One such alternative method is host-plant resistance, which uses naturally occurring plant defenses in crop cultivars to reduce the potential for yield loss from a pest population. Current soybean aphid-resistant cultivars do not protect against all soybean aphids due to the presence of virulent biotypes. In particular, soybean aphid biotype 4 is virulent to Rag1 and Rag2 resistance genes both individually and in combination. However, we hypothesized that resistance to biotype 4 may exist in previously identified, but uncharacterized resistant soybean plant introductions (PIs). To test this, we evaluated 51 previously identified but uncharacterized soybean aphid-resistant PIs for their resistance to colonies of soybean aphid biotype 4 collected in separate site-years (Lomira, WI 2013; Volga, SD 2015, 2016). Free-choice tests identified 14 PIs with putative resistance to ‘Lomira13’, two to ‘Volga15’, and eight to ‘Volga16’ soybean aphid colonies. Follow-up, no-choice tests corroborated two to three resistant PIs per colony, and PI 437696, which was resistant to each of the three colonies and could aid in breeding efforts and an integrated approach to soybean aphid management.

The study of speciation genetics is primarily concerned with identifying the genetic traits that allow divergent selection to overcome the homogenizing effects of gene flow. Felsenstein reviewed this race between gene flow and selection, concluding that speciation with gene flow was unlikely under a “two-allele model” (where two traits were necessary for reproductive isolation) but that divergence could occur quite easily under a “one-allele model.” Despite this finding, much of the sympatric speciation research involving phytophagous insects has relied on a two-trait model, where insects evolve both preferences for and increased performance on novel host plants. Philopatry (a tendency to remain where one was born) is known to occur in phytophagous insects and is a single trait isolation mechanism. However, it is traditionally invoked as simply augmenting reproductive isolation. Species in the Enchenopa binotata complex are believed to have speciated in sympatry. They exhibit host plant prefe­rences, host specific performance advantages and strong philopatry. We experimentally shifted E. binotata to evolutionarily novel host plants. Previous research has demonstrated that the experimental population of insects possesses genetic variation in prefe­rence and performance to the novel host. The degree of philopatry at mating and egg-laying was assayed for the first four years under full choice conditions. Host plant preference and performance was assayed after eight years. Philopatry was an immediate and strong isolating mechanism, while preference for and performance on the novel host lagged. We therefore suggest that philopatry may be a more important mechanism in the early stages of a host shift than previously believed [Current Zoology 59 (5): 658-666, 2013].

The study of speciation genetics is primarily concerned with identifying the genetic traits that allow divergent selection to overcome the homogenizing effects of gene flow. Felsenstein reviewed this race between gene flow and selection, concluding that speciation with gene flow was unlikely under a “two-allele model” (where two traits were necessary for reproductive isolation) but that divergence could occur quite easily under a “one-allele model.” Despite this finding, much of the sympatric speciation research involving phytophagous insects has relied on a two-trait model, where insects evolve both preferences for and increased performance on novel host plants. Philopatry (a tendency to remain where one was born) is known to occur in phytophagous insects and is a single trait isolation mechanism. However, it is traditionally invoked as simply augmenting reproductive isolation. Species in the Enchenopa binotata complex are believed to have speciated in sympatry. They exhibit host plant preferences, host specific performance advantages and strong philopatry. We experimentally shifted E. binotata to evolutionarily novel host plants. Previous research has demonstrated that the experimental population of insects possesses genetic variation in preference and performance to the novel host. The degree of philopatry at mating and egg-laying was assayed for the first four years under full choice conditions. Host plant preference and performance was assayed after eight years. Philopatry was an immediate and strong isolating mechanism, while preference for and performance on the novel host lagged. We therefore suggest that philopatry may be a more important mechanism in the early stages of a host shift than previously believed.

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.

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is the primary pest of soybean, Glycine max L., in the north central region. After more than a decade of research and extension efforts to manage this pest, several consensus management recommendations have been developed for sustainable and profitable soybean production. A summary of integrated pest management (IPM) tactics for soybean aphid are discussed, including cultural, genetic, economic, and chemical controls. To date, sampling and timely foliar insecticides are routinely recommended to protect yield and delay genetic resistance to insecticides. Host plant resistance is a new tool that can regulate populations and reduce the reliance of insecticides to control soybean aphid. A combination of these management tools also will reduce overall production costs and minimize negative environmental effects such as human exposure, and mortality of beneficial insects and other animals.

Resistance to the soybean aphid (Aphis glycines Matsumura) was characterized in segregating populations from crosses of soybean [Glycine max (L.) Merr.] accession PI 71506 to susceptible cultivars, and compared to Rag1 resistance from the cultivar ‘Dowling.’ Two susceptible adapted cultivars were crossed with PI 71506 or Dowling. In no-choice greenhouse assays, resistance corresponded to a single dominant gene model for both the PI 71506-derived and Dowling-derived populations. Segregation of aphid resistance in SD1111RR × PI 71506 F2:3 populations in aphid field-cage trials also fit a single-gene model, as did segregation of aphid resistance in the F2:5 generation. However, other genetic effects may also contribute to aphid resistance from PI 71506. Comparison with Rag1 resistance from Dowling indicated that PI 71506 resistance was weaker than that associated with Rag1, but antixenosis resistance from PI 71506 was effective against an Ohio aphid biotype that has overcome Rag1 resistance.

The soybean aphid, Aphis glycines Matsumura, is a serious pest of soybean [Glycine max (L.) Merr.] in the USA and Canada, and a sporadic pest of soybean in Asia. Infestations by soybean aphid cause economic loss to soybean through reductions in seed yield and oil concentration. Aphid-resistant soybean lines are needed to supplant insecticides for managing soybean aphid, and resistant lines may be developed from both domesticated and wild soybean lines. Free-choice assays of 42 lines of wild soybean (Glycine soja Siebold and Zucc.) in this study identified line 99PI522233 as resistant to soybean-aphid biotype 1. That line was advanced for follow-up assays with wild soybean lines PI 469399 B, PI 507825, PI 507840 and PI 507843, which had previously been screened as aphid resistant. Line 99PI522233 had significantly fewer soybean aphids than other lines except the resistant check in the second and third weeks of a no-choice assay, but the four other putatively resistant lines did not show resistance in the no-choice assay. Thus, line PI99522233 may be advanced for genetic characterization of its resistance, and it should be tested for resistance against virulent soybean aphid biotypes.

The direct effects of three soybean parentages, each represented by an Aphis glycines-resistant and susceptible isoline, on the fitness and performance of two key predators (Orius insidiosus and Harmonia axyridis) were evaluated in the laboratory. Predators were reared from hatch through adulthood in Petri dishes with cut trifoliolate leaves of the designated soybean variety, using eggs of Ephestia kuehniella as surrogate prey to eliminate prey-mediated effects of the host plant. Preimaginal survival and development, sex ratio, adult longevity, fecundity, and size were compared among treatments and a no-plant control. An additional experiment compared life-history parameters of predators caged with soybean versus Ipomoea hederacea (ivyleaf morning glory). Aphid resistance reduced the adult longevity of H. axyridis, but O. insidiosus was unaffected by resistance traits. However, adult O. insidiosus lived longer on soybeans with Group C base genetics than the other soybean varieties. Other parameters were not affected by soybean base genetics or resistance, but both predators generally performed worse on soybean than on I. hederacea or no-plant controls. The results suggest that soybean varietal selection, particularly with respect to A. glycines-resistance, may directly affect biological control agents. Also, implications of the generally poor suitability of soybean for natural enemies are discussed within the context of current crop production practices.

Learning, defined as changes in behavior that occur due to past experience, has been well documented for nearly 20 species of hymenopterous parasitoids. Few studies, however, have explored the influence of learning on population-level patterns of host use by parasitoids in field populations. Our study explores learning in the parasitoid Aphidius ervi Haliday that attacks pea aphids, Acyrthosiphon pisum (Harris). We used a sequence of laboratory experiments to investigate whether there is a learned component in the selection of red or green aphid color morphs. We then used the results of these experiments to parameterize a model that examines whether learned behaviors can explain the changes in the rates of parasitism observed in field populations in South-central Wisconsin, USA. In the first of two experiments, we measured the sequence of host choice by A. ervi on pea aphid color morphs and analyzed this sequence for patterns in biased host selection. Parasitoids exhibited an inherent preference for green aphid morphs, but this preference was malleable; initial encounters with red aphids led to a greater chance of subsequent orientation towards red aphids than predicted by chance. In a second experiment, we found no evidence that parasitoids specialize on red or green morphs; for the same parasitoids tested in trials separated by 2 h, color preference in the first trial did not predict color preference in the second, as would be expected if they differed in fixed preferences or exhibited long-term (> 2 h) learning. Using data from the two experiments, we parameterized a population dynamics model and found that learning of the magnitude observed in our experiments leads to biased parasitism towards the most common color morph. This bias is sufficient to explain changes in the ratio of aphid color morphs observed in field sites over multiple years. Our study suggests that for even relatively simple organisms, learned behaviors may be important for explaining the population dynamics of their hosts.

One of the oldest questions in ecology is how species diversity in any given trophic level is related to the availability of essential resources that limit biomass (e.g. water, nutrients, light or prey). Researchers have tried to understand this relationship by focusing either on how diversity is influenced by the availability of resources, or alternatively, how resource abundance is influenced by species diversity. These contrasting perspectives have led to a seeming paradox '... is species diversity the cause or the consequence of resources that limit community biomass?' Here we present results of an experiment that show it is possible for species diversity and resource density to exhibit reciprocal causal relationships in the same ecological system. Using a guild of ladybeetle predators and their aphid prey, we manipulated the number of predator species in field enclosures to examine how predator diversity impacts prey population size. At the same time, we manipulated the abundance of aphid prey in discrete habitat patches within each enclosure to determine how smaller-scale spatial variation in resource abundance affects the number of co-occurring predator species. We found that the number of ladybeetle species added to enclosures had a significant impact on aphid population dynamics because interference competition among the predators reduced per capita rates of predation and, in turn, the overall efficiency of the predator guild. At the same time, spatial variation in aphid abundance among smaller habitat patches generated variation in the observed richness of ladybeetles because more species occurred in patches where predators aggregated in response to high aphid density. The results of our experiment demonstrate that it is possible for species diversity to simultaneously be a cause and a consequence of resource density in the same ecological system, and they shed light on how this might occur for groups of mobile consumers that exhibit rapid responses to spatial and temporal variation in their prey.

Peristenus digoneutis Loan (Hymenoptera: Braconidae) was introduced to the US for biological control of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), and has since spread through much of the northeast. The purpose of this study was to determine if P. digoneutis and a native congener, Peristenus pallipes (Curtis), parasitize L. lineolaris in strawberry (where it is a key pest), and what factors relate to parasitism levels. During 1997–1999 we monitored parasitism on 17 strawberry farms in 14 counties in eastern and western New York State. We found that in eastern NY (where P. digoneutis has been established since the early 1990s), overall mean parasitism was 19.7% (ranging from 0 to 70%), mostly by P. digoneutis. Mean parasitism was significantly lower (12.3%, ranging from 0 to 58%) in western NY (where P. digoneutis was first recorded in 1999), and was mostly by P. pallipes. P. pallipes parasitism was significantly lower in eastern than western NY, suggesting the potential for competitive interaction with P. digoneutis. The insecticide regime of a farm was an important factor influencing parasitism rate, which was 5- to 6.5-fold higher on organic or casually sprayed farms than on intensely treated farms, though pest density under these three regimes was not significantly different. L. lineolaris density, and parasitism rate in nearby alfalfa and abandoned fields were also significant factors for parasitism in strawberry.

The soybean aphid (Aphis glycines Matsumura) is a threat to soybean production in the Midwestern United States. Varieties containing the Rag1 soybean aphid resistance gene have been released with limited success in reducing aphid populations. Furthermore, virulent biotypes occur within North America and challenge the durability of single-gene resistance. Pyramiding resistance genes has the potential to improve aphid population suppression and increase resistance gene durability. Our goal was to determine if a pyramid could provide improved aphid population suppression across awide range of environments. We conducted a small-plot field experiment across seven states and three years. We compared soybean near-isolines for the Rag1 or Rag2 gene, and a pyramid line containing both genes for their ability to decrease aphid pressure and protect yield compared with a susceptible line. These lines were evaluated both with and without a neonicitinoid seed treatment. All aphid-resistant lines significantly decreased aphid pressure at all locations but one. The pyramid line experienced lower aphid pressure than both single-gene lines at eight of 23 location-years. Soybean aphids significantly reduced soybean yield for the susceptible line by 14% and for both single-gene lines by 5%; however, no significant yield decrease was observed for the pyramid line. The neonicitinoid seed treatment reduced plant exposure to aphids across all soybean lines, but did not provide significant yield protection for any of the lines. These results demonstrate that pyramiding resistance genes can provide sufficient and consistent yield protection from soybean aphid in North America.

Larvae of closely related parasitoid taxa often lack morphological differences that can be used for species level identification. Determining the parasitoid species present in a host population may require rearing, often a time-consuming process. To monitor field parasitism rates by several species of Peristenus wasps (Hymenoptera: Braconidae) that are natural enemies of Lygus (Heteroptera: Miridae), we have developed a two-step molecular approach. Polymerase chain reaction (PCR) of the COI gene with wasp-targeting primers is performed on DNA extracted from a Lygus nymph and the parasitoid larva (if any) therein. A positive reaction indicates parasitoid presence. A restriction digest of the PCR product then indicates which parasitoid species is present among known alternatives, and a diagnosis is achieved in days rather than weeks or months.

Host plant shifts by phytophagous insects are often hypothesized as means through which new species could genetically differentiate. For genetic divergence to occur between populations on original and novel hosts, the colonizing population must possess genetic variation in performance traits allowing use of and selection by the new host. To test for the existence of genetic variation in Enchenopa treehoppers for the use of novel host plants in the genus Viburnum , we performed a 4-way full sib analysis. Related insects were exposed to 4 different plant species in greenhouse and field settings: the original host plant and 3 novel host species. We estimated genetic variation in performance traits of male and female longevity, and female fecundity and calculated fitness values, nymphal survival, and male and female developmental time to adult eclosion. We found significant genetic variation in traits influencing both survival and reproduction. There were significant interactions between genotype and host, indicating some genotypes are more adept than others at using new hosts. We conclude that sufficient genetic variation exists in this population to facilitate successful shifts to these new hosts.

Spotted alfalfa aphids (Therioaphis maculata, Buckton) are a major pest of alfalfa in the arid western United States, yet are rarely encountered in Wisconsin. In Wisconsin, where severe drought conditions are rare, pea aphids (Acyrthosiphon pisum, Harris) are the predominant aphid herbivore in alfalfa. An unusually dry growing season in south-central Wisconsin in 2003 presented us with an opportunity to test two ideas. First, we conducted surveys to determine whether, due to the dry growing season, A. pisum density was lower than normally observed and the density of the more drought-tolerant T. maculata (Mittler and Sylvester, 1961) was greater in these dry areas. Second, we designed an experiment to determine whether these patterns were the result of environmentally mediated competition. We define this as competition between multiple species where the superior competitor is not fixed, but rather determined by the state of a variable environment (in this case, whether the water content of alfalfa determines which aphid species is the superior competitor). This type of competition is common in nature (Huston, 1979).

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an economically important pest of soybean, Glycine max (L.) Merrill, in the United States. Phenological information of A. glycines is limited; specifically, little is known about factors guiding migrating aphids and potential impacts of long distance flights on local population dynamics. Increasing our understanding of A. glycines population dynamics may improve predictions of A. glycines outbreaks and improve management efforts. In 2005 a suction trap network was established in seven Midwest states to monitor the occurrence of alates. By 2006, this network expanded to 10 states and consisted of 42 traps. The goal of the STN was to monitor movement of A. glycines from their overwintering host Rhamnus spp. to soybean in spring, movement among soybean fields during summer, and emigration from soybean to Rhamnus in fall. The objective of this study was to infer movement patterns of A. glycines on a regional scale based on trap captures, and determine the suitability of certain statistical methods for future analyses. Overall, alates were not commonly collected in suction traps until June. The most alates were collected during a 3-wk period in the summer (late July to mid-August), followed by the fall, with a peak capture period during the last 2 wk of September. Alate captures were positively correlated with latitude, a pattern consistent with the distribution of Rhamnus in the United States, suggesting that more southern regions are infested by immigrants from the north.

Annual monitoring surveys for the endangered American burying beetle, Nicrophorus americanus Olivier, have been conducted in south central South Dakota since 1995. The population has been stable in abundance and distribution. Two mark and recapture surveys were conducted in June and August, 2005 in southern Tripp County, South Dakota, U.S.A. Using baited pitfall traps, we captured and marked 168 specimens of N. americanus during 410 trap-nights in June. In August, 323 specimens were captured and marked in 450 trap-nights. We estimated the population size of N. americanus in an area of approximately 220 km2. Estimates were obtained using a family of models (program CAPTURE) that incorporate several sources of variability in probability of capture. The June population estimate (±1 SE) was 442 ± 73 and a 95% confidence interval of 333–624 adults. The August population estimate (±1 SE) was 901 ± 117 with a 95% confidence interval of 714–1,177 tenerals and adults combined.

1. One of the oldest questions in ecology is how species diversity in any given trophic level is related to the availability of essential resources that limit biomass (e.g. water, nutrients, light or prey). Researchers have tried to understand this relationship by focusing either on how diversity is influenced by the availability of resources, or alternatively, how resource abundance is influenced by species diversity. These contrasting perspectives have led to a seeming paradox '... is species diversity the cause or the consequence of resources that limit community biomass?' 2. Here we present results of an experiment that show it is possible for species diversity and resource density to exhibit reciprocal causal relationships in the same ecological system. Using a guild of ladybeetle predators and their aphid prey, we manipulated the number of predator species in field enclosures to examine how predator diversity impacts prey population size. At the same time, we manipulated the abundance of aphid prey in discrete habitat patches within each enclosure to determine how smaller-scale spatial variation in resource abundance affects the number of co-occurring predator species. 3. We found that the number of ladybeetle species added to enclosures had a significant impact on aphid population dynamics because interference competition among the predators reduced per capita rates of predation and, in turn, the overall efficiency of the predator guild. At the same time, spatial variation in aphid abundance among smaller habitat patches generated variation in the observed richness of ladybeetles because more species occurred in patches where predators aggregated in response to high aphid density. 4. The results of our experiment demonstrate that it is possible for species diversity to simultaneously be a cause and a consequence of resource density in the same ecological system, and they shed light on how this might occur for groups of mobile consumers that exhibit rapid responses to spatial and temporal variation in their prey.