Update:
This report covers Year 2 in a 3-year ongoing project on management and outreach of soybean insects in the North Central region. The report contains three sections. The first section is on the scientific and extension deliverables generated in Year 2 of this project. These deliverables all contain information generated in NCSRP-funded work. The second section is a narrative of current progress. The third section is a list of the project metrics written into our proposal for Year 2, and their status.

During the reporting period we published 33 scientific journal papers, gave 33 presentations at scientific meetings, and organized 2 scientific symposia on soybean pest management. Breeding efforts produced 4 varieties now under commercial production, and 8 experimental lines under field evaluation and experimentation. There were 18 students or postdocs graduated or in training on projects related to NCSRP research. We gave 75 extension presentations to farmers and other crop professionals containing NCSRP research. We wrote 18 extension articles and published 14 extension publications. A highlight of these publications is the field guide, Stink Bugs of the North Central Region, a field-friendly pocket-sized booklet on stink bug identification, biology and management. 6000 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. Other extension deliverables include hands-on scouting exercises designed to be used at winter meetings to teach soybean management techniques. During the reporting period we earned $588,000 in additional funding related to our NCSRP-generated research, showing the power of NCSRP funding to leverage resources for soybean research. Finally, members of our group received 6 awards for NCSRP-related work during the reporting period. In a noteworthy honor, we received the International IPM Award of Excellence for an IPM team. This award will be conferred at the 9th International IPM Symposium in March, 2018.

These deliverables are documented in detail in the attached version of this report.

View uploaded report

I. Extension and Outreach

We gave 75 extension presentations to farmers and other crop professionals containing NCSRP research. We wrote 18 extension articles and published 14 extension publications. A highlight of these publications is the field guide, Stink Bugs of the North Central Region, a field-friendly pocket-sized booklet on stink bug identification, biology and management. 6000 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. Other extension deliverables include hands-on scouting exercises designed to be used at winter meetings to teach soybean management techniques. These deliverables are documented in detail in the attached version of this report.

II. Insect Monitoring and Management

1. Stink bug monitoring and management: This is the second year of a 3-year study. The goal is to devise management thresholds for stink bugs that are specific to the North Central Region. In 2017, Michigan was added to the project, resulting in a total of 9 states. Work continues on identifying stink bugs from summer sampling and analyzing data. Some additional data collection will be conducted in Year 3 of the project, and final data analysis completed.

2. Pollinator diversity and soybean yield: The goal of this study is to document the diversity of pollinators present in soybean fields. Pollinators may enhance soybean yield, and soybean may serve as an important reservoir for pollinator biodiversity. Participants in ND, SD, IA, OH, MN, NE, IN, MO, WI collected pollinators in soybean fields. Bees identified from soybean to date include 5,513 individual bees representing 71 species in 17 genera and five families. This is an increase of 14 species compared to the 2014 survey. While only three states are done, the remaining six states (MO, IA, WI, MN, SD, ND) have two fields each and not as many individuals, so identification of bees is about 50% done. Syrphid flies (also important pollinators) will be identified after bees are finished. For the project to assess the diurnal activity of wild and managed bees in soybeans: Currently the EPA requires farmers to limit their application of insecticide to periods when bees are not on flowers to reduce exposure. Honey bees (and other bees) typically fly only during periods of daylight, which limits applications to dusk. Some commercial applicators have questioned whether honey bees are active throughout the entire day or if they limit their foraging to optimal periods of activity, when temperatures are not at their highest. In order to gain a better understanding of this topic we conducted a study to determine the diurnal activity of honey bees and other bees in soybean fields growing in a variety of environments along a nationwide transect, from Mississippi to South Dakota. Sampling took place once a week from R1 to R4. These data are still being processed. We are also planning how to approach this objective in Year 3 of the project, during the summer of 2018.

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 a DIY assay kit to test aphids for resistance to thiamethoxam insecticide. Our resistance monitoring has detected shifts in tolerance in certain soybean aphids, but the shifts are very low. We have also fine-tuned the bioassays used to monitor this resistance with various improvements. We have developed this technique to the point where it can be used as a research tool. However, we have concluded that it will not work to develop this as a “do-it-yourself” kit for ag professionals. We have tried many methods to make this user-friendly for crop consultants. However, the soybean aphid has proven too delicate for the DIY kit approach unless the end-user is trained to handle these types of insects. Too much soybean aphid injury and mortality occurs during aphid transfer. However, we have developed the methodology to the point where it is a useful research tool for trained researchers involved in resistance monitoring. Instead of further effort to develop a kit for widespread use, we are shifting our focus to aphid genetics as a component of resistance monitoring. Dr. Andrew Michel’s Lab (Ohio) has been assisting with genetic typing and development of clonal lineages. One hundred-sixty clonal populations were sent to Nebraska and each population is undergoing requisite population increase needed for bioassay.

4. Monitoring for aphids, thrips, and soybean vein necrosis: Soybean vein necrosis virus is transmitted by thrips. We sampled thrips from suction traps in 6 states. We have completed thrips survey for the 2016 growing season and begun processing the 2017 samples. There does not appear to be much thrips activity in May in most of the locations. Thrips populations start to increase in June which coincides with early vegetative stages of soybean in most Midwest states. The northern states don’t seem to have high thrips numbers even in June. Thrips activity peaked in July-August in most states and begins a decline in September. Populations of thrips vectors of SVNV are high during July-August in most locations. This coincided with appearance of the disease in IN but we did not receive any SVNV samples from other states. Regarding suction trap monitoring for soybean aphid population trends: The Midwest Suction Trap Network (MSTN) operates in 8 states with a total of 31 locations. A representative set of archival aphid slides from aphids collected in the MSTN have been made to be deposited in the INHS Insect Collection Museum. Online 3I Interactive Key for Aphis species in the Midwest USA has been updated to easy access http://dmitriev.speciesfile.org/key.asp?key=Aphis&lng=En&i=1&keyN=1). Suction trap samples collected in 2016 and 2017 have been shared with Punya Nachappa to monitor mainly soybean thrips. We have decided that the best home for the MSTN data is the Center for Invasive Species & Ecosystem Health at the University of Georgia (https://www.bugwood.org/). The suction trap data files are ready to be shared as soon as we communicate with the responsible of this database system. Moreover, emphasis on extension will be focus with the data collected from the MSTN.

5. Technology development: The goal is to develop an aphid-counting app. We are currently approximately 70% done with processing images collected over the past two summers (approx. 3000 total). Currently, mobile device cameras equipped with the android operating system are able to detect more aphids on infested soybean leaflets compared to iOS-based devices when using our aphid counting software. Work on this objective will continue in Year 3 of the project.


III. Resistant Varieties and Biotypes

1. Breeding for resistant varieties: The Diers program is developing and releasing soybean varieties with aphid resistance. The backcrossing of the aphid resistance genes Rag4 and Rag6 into cultivars that already have Rag1, Rag2, and Rag3 is continuing. During the summer of 2017, we produced BC3F1 seed for Rag6 in both the MG I Titan background and the MG II LD02-4485 background. The BC3F1 seed is being planted in the greenhouse so that the fourth and final backcross can be conducted early this winter. For Rag4, we completed the backcrossing of this gene in both backgrounds and now this gene is being combined with Rag1-3. In the LD02-4485 background, crosses were made this summer between plants with Rag4 backcrossed into them and Rag1-3 backcross plants. F1 seed from these crosses will be planted in the greenhouse to develop populations segregating for all four genes. In the Titan background, populations of F2 plants segregating for Rag1-4 were grown in the field this past summer. This winter we will grow plants in a greenhouse from these populations to identify those plants with the resistance allele for all four genes. These plants will then be crossed to backcross plants with Rag6 to complete the stacking of all five genes. Breeding to develop new cultivars with Rag1, Rag2 and stacks of Rag1 and Rag2 is continuing. Experimental lines with different combinations of these resistance genes were yield tested in 2017 and we are awaiting the completion of harvest so results from these tests can be summarized and selections made. In addition, commercial production or commercial scale seed increases are occurring for one variety with Rag1 only, four varieties with Rag2 only, and two varieties with Rag1 and Rag2 stacked together. These varieties are being sold under the Illini Brand name or are being licensed to other companies for their branding.

2. Aphid virulence genotyping and mapping: Our goal is to map aphid virulence. Genetic mapping of virulence has revealed segregation distortion among B1 and B2 reciprocal crossed. In other words, the ratio of genotypes in the F1 generation is not what was expected. Some offspring of this cross appear to be either sterile or inviable. Survivors in the F1 generation appear similar to the female genotype regardless of biotype (i.e. female drive). Reasons for this phenomena include disparate genetic divergence between biotypes 1 and 2 (which has also been observed), or drastically different bacterial symbionts (which is currently being studied). We observed high migration to buckthorn this past autumn and have made collections. These samples will be genotyped and compared to aphids already collected from 2017. Populations include Iowa, Minnesota and Ohio. Aphids from the above collections will also be screened for phenotyping on Rag varieties. Based on the segregation distortion and female drive, we are comparing and genotyping Wolbachia from the soybean aphid. Wolbachia is a bacteria that can be found within insects that often induces mating incompatibilities. If indeed crosses of B1 and B2 are infertile, then the spread of virulence may be more rapid and place more emphasis on a refuge.

3. Aphid virulence management for resistant varieties: During the 2017 growing season we completed a field 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 to using aphid-resistant soybeans. The purpose of this study is to find ways to maximize the longevity of aphid resistant varieties while minimizing yield loss in refuges. Data from 2017 are being analyzed. Another field season of data will be collected in Year 3 of this study. Preliminary data assessments from Iowa show that all options using the aphid resistant line, regardless of how much susceptible soybean was mixed in, had lower aphid populations than the plots with only aphid-susceptible soybeans. These data will inform modelling to determine the likely success of a Refuge-in-a-Bag resistance management plan for the soybean aphid.

4. Economic returns on resistant varieties: This is a three-summer study designed to assess the economic returns on herbicide tolerant and aphid resistant traits. We completed the second year of a field study replicated at two locations in Iowa to determine the optimal economic approach to pest management for soybean production. In 2016 and 2017, we compared four varieties that varied by aphid-resistance and herbicide-tolerance. In replicated plots, each variety was planted either early (May) or late (June) to determine if the yield potential varies. All varieties were treated with insecticide if aphid outbreaks occurred. Overall, aphid-resistant soybeans regardless of the background genetics prevented aphid outbreaks, and did not need an insecticide application. As observed in parts of Iowa and Minnesota, the insecticide applied to aphid-susceptible varieties did not provide expected control. Yield data are pending. So far, these data suggest that farmers can achieve the same yield by reducing inputs. A third field season of experiments will be conducted in Year 3 of this study.

IV. Biological Control

We worked with researchers from 12 states in the NCSRP network, and each scouted three times over the summer of 2017. They provided information on soybean aphid pressure and the per-plant density of black (Aphelinus) parasitoid mummies in each state, and sent samples of black mummies to the Heimpel laboratory at the University of Minnesota for identification. Soybean aphid was first detected in June across the northern tier of states - North Dakota, Minnesota, Iowa, Wisconsin, and Michigan (see maps, below). By mid July there were high densities of aphids in North Dakota, Minnesota, Iowa, and Illinois, and aphids reported in South Dakota and Nebraska; Minnesota had aphid densities above the economic threshold of 250 aphids per plant. In August soybean aphid pressure above the action threshold was reported in Minnesota and Iowa, substantial aphid numbers were found throughout the region, but no aphids were reported for the entire summer in Kansas, Missouri, and Ohio. These trends compare very closely with the numbers of A. glycines captured by the Suction Trap Network, which confirmed that Kansas and Missouri had no reports of the aphid.

The parasitoid A. certus was first reported in North Dakota on June 26th, and was found in Michigan in June as well. The parasitoid was also found in Minnesota, Iowa, Illinois, and Indiana at densities between 0.6 and 2.0 parasitoids per plant by the end of summer. A pattern of the aphid and its parasitoids seems to be centered in the north and west, spreading south and east during the summer but remaining most prevalent in Minnesota and Iowa. The parasitoid, and to some extent the aphid as well, was first detected in the northwest, in the relatively small soybean acreage of North Dakota, and despite movement southward, neither the parasitoid nor the aphid were detected in the southernmost nor easternmost states.
Aphelinus certus was the dominant parasitoid in the survey although the native parasitoid Lysiphlebus testaceipes was found in Iowa, Indiana, Michigan, and Minnesota as well. The level of hyperparasitism was relatively high for Aphelinus at 21% and included species in the genera Alloxysta (Hymenoptera: Figitidae), Dendrocerus (Hymenoptera: Megaspilidae), Asaphes (Hymenoptera: Pteromalidae), and Syrphophagus (Hymenoptera: Encyrtidae).