Updated February 3, 2019:
A full Technical Report is provided in the attached document.

Summary

This report covers a 3-year project on management and outreach of soybean insects in the North Central region, involving 21 researchers in 10 states. The report contains four sections (1) a non-technical summary; (2) a detailed technical summary; (3) project deliverables; (4) performance metrics as of the third/final year of the project. During the 3-year reporting period we published 55 scientific journal papers, gave 105 presentations at scientific meetings, and organized 6 scientific symposia on soybean pest management. We gave 191 extension presentations containing NCSRP results to farmers and other crop professionals. We wrote 82 extension articles and published 73 extension publications and other outreach products utlizing NCSRP results. We trained 32 students or postdocs on this project, who are the researchers of the future.

During the reporting period we earned $5.27 million in additional leveraged funding related to our NCSRP-generated research (over a 350% return on NCSRP’s investment), showing the power of NCSRP funding to leverage additional resources for soybean research. Finally, members of our group received 13 awards for NCSRP-related work during the reporting period. In two noteworthy honors, we received the International IPM Award of Excellence for an IPM team and the ESA Plant-Insect Ecosystems IPM Team Award to members of the group led by Bob Koch. Two members of our team (Kelley Tilmon and Erin Hodgson) have receive the Entomological Society of American NCB Distinguished Achievement Award in Extension.

Some highlights of our results include the following:
• We performed the first comprehensive survey of the stink bug species of the North Central Region.
• We determined a new sampling plan for stink bug sampling in soybean that’s specific to the North Central Region.
• We documented an amazing diversity of pollinator species found in flowering soybeans, with 108 species of bees and 11 species of pollinating syrphid flies. This is a landmark study on pollinator diversity in the region.
• We developed three new tools to monitor for soybean aphid resistance to the insecticide thiamethoxam.
• We established a baseline susceptibility to thiamethoxam which can be used in future insecticide resistance studies, and documented the first reduced susceptibility to this insecticide.
• We have made the 13 year regional sampling data from the aphid suction trap network publicly available online through the Center for Invasive Species and Ecosystem Health.
• We have documented season trends and species composition of thrips which are the vector for soybean vein necrosis virus.
• We have developed experimental soybean lines containing all possible combinations of five resistance genes (32 combinations) in both a MG I and MG II background for further work on aphid-resistant soybeans.
• Soybean lines with the resistance genes Rag1, Rag2, and a pyramid of both have been released.
• We sequenced the soybean aphid genome.
• We have maintained research colonies of the four known soybean aphid biotypes.
• We have performed evaluations of soybean aphid virulence and screenings for new sources of resistance.
• We have determined that a refuge-in-a-bag approach with a 25% susceptible blend can protect soybean yield while serving as a suitable refuge to delay the development of aphid biotypes.
• We used field studies to ground-truth the economic viability and in many cases superiority of growing aphid-resistant varieties.
• We have documented the spread of the effective aphid biological control agent Aphelinus certus through much of the North Central Region.

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Program Area I. Extension and Outreach

We gave 105 extension presentations to farmers and other crop professionals containing NCSRP research. We wrote 82 extension articles and published 73 extension publications and other outreach products such as videos, website, and webinars. A highlight of these publications is the field guide, Stink Bugs of the North Central Region, a farmer-friendly pocket-sized booklet on stink bug identification, biology and management. 9000 free hard copies of this field guide have been distributed through universities and state checkoff organizations, and made available as a free download on SRII and other websites. Another noteworthy extension publication on our results, The Effectiveness of Neonicotinoid Seed Treatments in Soybean, is a joint factsheet publication of North Central Land Grant Universities. This regional factsheet informs farmers about the relative costs and benefits of seed treatments for pest control in soybean, to help them with their input decisions. Another regional publication, distributed to producers through the 12 North Central Land Grant universities and through the SRII website, is Management of Insecticide-Resistant Soybean Aphids, the first extension publication to alert producers to the rise of insecticide resistance in soybean aphids in the Dakotas, Minnesota, and Iowa. We have published a new, updated 2nd edition of the popular Soybean Aphid Field Guide, a farmer reference for soybean aphid management in the North Central Region. Finally, NCSRP research on pollinators in soybean was used to inform a joint publication of the USDA, USB and the Honey bee Health Coalition on Best Management Practices (BMPs) for conserving pollinators that use soybeans as forage, and members of our team served on the technical committee which drafted this document.

Additional extension deliverables are detailed in the Deliverables section below. All of these deliverables help to make the knowledge gained through NCSRP research available to farmers in a form they can use.


Program Area II. Insect Monitoring and Management

1. Stink bug monitoring and management: The goals were to (1) determine the range and abundance of different stink bug species throughout the region to document the extent of the problem, and (2) devise sampling plans for stink bug that are specific to the North Central Region. Our findings are useful for farmers because they provide research-based recommendations on how to effectively sampling these emerging pests of soybean to make management decisions. This work was conducted in a coordinated protocol across 3 years in 9 states, sampling and identifying stink bug species in multiple soybean fields per state. Brown stink bugs (comprised of a few species) were more abundant in the northwestern part of the region, whereas the green stink bug was more abundant in the southeast. The invasive brown marmorated stink bug was most abundant in the eastern part of the region and was detected in soybean in Minnesota for the first time. The second objective developed research-based scouting recommendations (a sampling plan) to estimate stink bug numbers in soybean, which can then be related to an economic threshold for pest management decision making. We found that an average of 40 sample units per field are necessary to achieve acceptable precision in most areas but can be as low as 5–10 units in some parts our region where stink bug densities are higher.

2. Pollinator diversity and soybean yield: The goals of this study were to (1) document the diversity of pollinators present in soybean fields, and (2) assess the time of day when bees are most active in soybean to aid with spray decisions. Pollinators may enhance soybean yield even though soybeans are self-pollinating, and soybean may serve as an important reservoir for pollinator biodiversity. It is relevant for farmers to understand what pollinators occur in their fields. Participants in 9 states collected pollinators weekly in flowering soybeans during two project-years. We found a surprising abundance and diversity of pollinator species. A total of 10,822 bees have been identified comprising 108 species in 27 genera and 5 families, and 1,190 syrphid flies have been identified comprising 11 species in six genera. More details are available in the Technical Report.

Based on the insecticide labels, farmers are required to limit their application of insecticide to periods when bees are not on flowering plants. For soybeans, this can be challenging as insect pest outbreaks can occur when soybeans are flowering. This flowering period can last several weeks with the amount of flowers changing over time. We asked if the abundance of bees in soybeans varied during this flowering period. Furthermore, honey bees and other wild bees typically fly only during periods of daylight, which limits application to dusk. Some commercial applicators have questioned whether honey bees are active throughout the day. They have asked if honey bees limit their foraging to optimal periods of activity, when temperatures are not at their highest. Empirical evidence is lacking on the activity on diurnal activity of honey bees in soybean fields. In this study, we collected honey bees and wild bees on a timed basis throughout a day for soybean fields grown in a variety of environments along a nationwide transect, from Mississippi to South Dakota and as far east as Ohio. Data are currently being combined and analyzed. These data will help provide concise information about how bees use soybean fields in the North Central region. This information can be valuable to improve management strategies for the application of insecticides to soybeans while also conserving pollinators within those fields.


3. Soybean aphid insecticide resistance: The goals of this objective are to monitor for soybean aphid resistance to the insecticide thiamethoxam in the North Central Region, and to develop assay protocols to test aphids for resistance to thiamethoxam insecticide. This is important for farmers because when aphids develop insecticide resistance farmers lose management options and must adjust accordingly. Three bioassay techniques were developed/optimized to test soybean aphids for susceptibility to thiamethoxam insecticide. 1. Glass vial – A quick contact bioassay method for monitoring insecticide susceptibility. 2. Detached-leaf – A systemic bioassay method for monitoring insecticide susceptibility and for conducting resistance research. 3. Whole-plant – a systemic bioassay method for in-depth study of insecticide resistance and plant response research. Regional monitoring of soybean aphid populations for thiamethoxam susceptibility indicated a small decrease of susceptibility and the presence of sublethal effects. As a result of this study we now have bioassys for monitoring both bean leaf beetle and soybean aphid susceptibility to thiamethoxam. We have the first indication that soybean aphid susceptibility to thiamethoxam, is decreasing, and a baseline susceptibility data set for monitoring changes in soybean aphid resistance to thiamethoxam in the future.

4. The Midwestern USA aphid suction trap network (STN) was begun in 2005 as a way to monitor soybean aphid populations and other pests, and has been in continuous seasonal operation since then. It covers a broad geographic area: between 2016 and 2018 the network operated in 9 states with a total of 31 locations with cooperative funding from NCSRP and state, local, and business collaborators. In collaboration with Joseph LaForest (Department of Entomology, Center for Invasive Species and Ecosystem Health, University of Georgia; Southern IPM Center) in kind support, a voluminous collection of records of sample identifications and observations from the STN are now publicly available at https://suctiontrapnetwork.org/ and https://www.eddmaps.org. These data allows for studies on distribution of known species and new or non-identified species captured by the suction traps. The information gleaned from the suction trap network is important for the growers and researchers interested in insect pests and their occurrences and distribution over time and geographic space. The compiled information provides the basis for potential management, long-term dispersion studies, and an early warning for insect pest outbreaks including those caused by exotic introductions. A more complete summary of STN results is available in the full technical report.

Monitoring for aphids, thrips, and soybean vein necrosis: Soybean vein necrosis virus (SVNV) is transmitted by thrips. Our goal was to monitor thrips abundance and activity as an indicator of where SVNV risk is highest in the North Central Region. We sampled thrips and identified species from suction traps in 6 states across two years, with samples obtained from the suction trap network supported by this project. Overall, thrips counts were similar in 2016 and 2017 across the states that we sampled. The populations start to build as early as May which coincides with early vegetative stages of soybean in some Midwestern states. Thrips activity peaked in July-August in most states and begins a decline in September. The most common thrips species in the samples were eastern flower thrips followed by soybean thrips, both of which can transmit SVNV, although soybean thrips is the more efficient vector. We are in the process of completing counting and identification for 2018 samples, but preliminary data suggests similar trends as the previous years.


5. Technology development: This objective includes work towards developing an aphid-counting app; the development of an electronic resource myFields.info which is designed to house integrated Extension information that is dynamic in nature with (see http://myfields.info/schematic), with interactive tools and resources that link agricultural information from different sources together; and digitizing the soybean aphid Speed Scouting sampling method to provide real-time decisions for managing aphids. These tools are described in greater detail in the Technical Report. The development of technical tools is important to give farmers new and more efficient avenues for pest management decision making and execution.


Program Area III. Resistant Varieties and Biotypes

1. Breeding for resistant varieties: The Diers program is developing and releasing soybean germplasm and varieties with aphid resistance. Aphid-resistant varieties are important to give farmers new, effective, convenient tools for aphid management (especially in light of insecticide resistance in soybeans aphids, which has now been documented). he breeding activities of this project have focused on developing soybean experimental lines that are useful for researchers and new aphid resistance varieties for farmers. The experimental lines being developed for researchers have different combinations of five aphid resistance genes in both a MG I and a MG II background. There will be 32 different lines developed in each background with each line having a different combination of the genes that range from having all five resistance genes to having no genes. These lines will be very useful to researchers who are testing the yield effect of these genes and are determining what combinations of genes best protects soybean from aphids. This usefulness was demonstrated by research that was done using lines that we previously developed with different combinations of three aphid resistance genes. Final selection of plants that will be used to develop these lines will be completed this spring in a greenhouse and the selected lines will be increased in the field this summer.

There has been limited availability to farmers of varieties that have resistance to soybean aphid. Through the project, we have been developing varieties that have the resistance genes Rag1, Rag2 and the combination of the two genes (Rag1+Rag2). Varieties with these genes have been released for commercial production and a seed producer in Illinois is currently producing seed of a variety with Rag1+Rag2, a second with Rag1, and a third with Rag2.

2. Aphid virulence genotyping and mapping: Our goal is to genetically map aphid virulence. Soybean aphid virulence is when aphids are able to overcome our resistant varieties, and important issue for farmers who may wish to grow them. Our goal of understanding soybean aphid virulence involved several objectives. We sequencing the entire soybean aphid genome. Freely available at AphidBase, the soybean aphid genome represented the 4th aphid genome, as well as the smallest genome to date (302 mega basepairs). This genome will serve as a genetic foundation to investigate virulence as well as facilitate future objectives such as insecticide resistance (funded on the current NCSRP project). We also compared genes that the aphid biotypes differentially expressed, and found several effector genes with lower expression in the virulent aphid. Aphids use effectors to control or evade plant defenses, therefore the virulent soybean aphid may not express effector(s) that the soybean plant uses to recognize aphid attack. Third, we used mapping approaches to determine that soybean aphid biotypes may not mate randomly, which made identifying markers or the gene for virulence complicated. Nonetheless, our data suggest that virulence may not have a genetic basis, but yet be caused by epigenetic processes (i.e. differences in gene expression).

Aphid biotypes: Colonies of four known soybean aphid biotypes maintained at the USDA-ARS laboratory located the National Soybean Research Center at the University of Illinois are often used to compare field collections so that unknown clones can be classified or typed. Between 2016 and 2018 these clones have been shared with multiple researchers as part of this project.

Evaluation of soybean aphid virulence: We completed a study to evaluate the virulence of field collected soybean aphid clones on soybean genotypes with known soybean aphid resistance genes. Fourteen aphid clones collected on soybean and buckthorn (Rhamnus cathartica L.) plants in 2015 and 2017, along with four known aphid biotypes (from stock cultures) were evaluated. We found that the field collected clones were not of all the same biotype. None of the biotypes and field clones from Illinois, Indiana and South Dakota overcame the resistance of soybean PI437696.

Evaluation of soybean resistance: This information is useful to soybean growers since soybean breeders will use these soybean lines to develop more resistant soybean cultivars. Soybean resistance expressed in five plant introductions (PIs) to four soybean aphid biotypes was characterized to determine the mode of resistance inheritance, and identify markers associated with genes controlling resistance in these accessions. Five soybean PIs, from an initial set of 3000 PIs, were tested for resistance against soybean aphid biotypes 1, 2, 3, and 4 in choice and no-choice tests. Of these five PIs, three expressed antibiosis against all four biotypes, while two expressed antibiosis against biotypes 1, 2, and 3. The five soybean plant introductions expressed antibiosis resistance to multiple soybean aphid biotypes with two introductions having resistance genes located in the Rag1, Rag2, and Rag3 regions, two introductions having resistance genes located in the Rag1 and Rag2 regions, and one introduction having a resistance gene located in the Rag2 region.

3. Aphid virulence management for resistant varieties: The purpose of this study is to find ways to maximize the longevity of aphid resistant varieties (delaying the development of biotypes that are virulent on them) through the use of a blended refuge of resistant and susceptible varieties – while at the same time minimizing yield loss. We performed a 3 year field study study in three states (Iowa, South Dakota, and Ohio) in quarter-acre, replicated plots to measure the impact of a Refuge-in-a-Bag approach, testing different percentage blends of susceptible seed. Overall, our data suggests that aphid-resistant soybeans blended with a minimum of 25% aphid-susceptible plants could serve as a refuge while still being effective for suppressing aphids in the field. Plots with interspersed refuge may produce a higher proportion of late-season avirulent individuals which is consistent with refuge requirements. Thus, inclusion of an interspersed refuge could be a viable resistance management strategy for soybean aphid. In short, the addition of susceptible seeds does not alter the ability of Rag to provide season-long aphid and yield protection; refuge fields produce a higher proportion of avirulent individuals than all-resistant fields; going forward, adherence to refuge inclusion could be a viable insect resistance management strategy for the sustainable use of Rag traits

4. Economic returns on resistant varieties: This was a year study designed to assess the economic returns on herbicide tolerant and aphid resistant traits. The goal was to determine the optimal economic approach to pest management for soybean production. This project was conducted in two parts: a field research component and a computer-based modeling economic analysis. The economic analysis is on-going and currently being refined, but the field research spanned two growing seasons and was completed in 2017. We compared four varieties that varied by aphid-resistance and herbicide-tolerance. Our findings indicate that if farmers in aphid-prone areas adopt resistant varieties they can maintain or improve profitability. This may be even more true in areas where aphids have developed resistance to commonly used insecticides. Soybean aphid-resistant varieties cost the same as similar susceptible varieties and do not cause yield loss, all while protecting plants from soybean aphids and eliminating insecticide applications, another input cost. Our preliminary results from the economic analysis show increased profitability for soybean farmers when they use resistant varieties.


Program Area IV. Biological Control

Asian parasitoids of soybean aphid have the potential to provide biological control of soybean aphid, reducing the need for applications of foliar insecticides. If we can understand the conditions required for the overwintering survival of these parasitoids, we will be better able to predict where and when these parasitoids will be most successful at reducing soybean aphid pressure below the economic threshold, reducing the need to apply insecticides. We studied the overwintering biology of Aphelinus parasitoids to better understand if the winters in the Northern US might limit the success of these parasitoids as biological control agents. We used field studies to determine the usefulness of various habitats for successful overwintering and lab studies to determine the minimum temperatures that these insects can withstand. We found that survival of overwintering parasitoids was much higher when they were placed on the ground in the fall and subsequently covered by snow than when they were placed on buckthorn branches, the overwintering host plant of soybean aphid. Finally, we conducted field surveys to determine where on the landscape these parasitoids are attempting to spend the winter. We surveyed both soy fields and buckthorn in Minnesota in the fall of 2018 and while we found diapausing parasitoids in both habitats, we found many more in soy fields and almost exclusively unparasitized aphids on buckthorn plants. e also conducted a sampling program to establish the range of the very effective soybean aphid parasitoid Aphelinus certus. Our surveys showed that Aphelinus certus is present throughout the North Central region. More details are available in the Technical Report.