Progress report for LNC22-464
Project Information
Title: Biological control for sustainable management of soybean gall midge, a new pest of soybean in the North Central Region.
This research-based project aims to advance implementation of biological control for soybean gall midge, Resseliella maxima (Diptera: Cecidomyiidae). Soybean gall midge is a new pest posing a significant threat to soybean production in the North Central Region. This pest infests the stems of soybean plants and has caused considerable yield reductions in multiple states. Research is urgently needed to understand the potential for biological control, specifically the community composition, dynamics and impacts of parasitic wasps on soybean gall midge populations. Over three field seasons, soybean fields of cooperating farmers will be sampled for this pest and its natural enemies. Parasitic wasps (parasitoids) will be identified through rearing from field-collected soybean gall midge larvae in the laboratory, and molecular methods to quantify parasitism of field-collected soybean gall midge larvae. Data will be analyzed to examine the spatiotemporal dynamics of the communities of parasitic wasps and their relationship to surrounding habitats. This knowledge on biological control of soybean gall midge will be essential for the implementation of sustainable IPM programs for this pest. A primary near-term outcome (upon completion of the project) will be knowledge of what species of parasitic wasps attack soybean gall midge across the region and what levels of biological control they provide. An additional near-term outcome (upon completion of the project) will be knowledge of the spatial and temporal dynamics of parasitism of soybean gall midge. Spatial models will be developed to allow identification of landscape features associated with high and low levels of potential biological control. Temporal models will be developed to determine the seasonal abundance (phenology) of the pest and parasitic wasps. A longer-term outcome will be improved knowledge for rearing the parasitic wasps that attack this pest, which could lead to development of future programs universities or government agencies to produce these parasitic wasps for release against this pest (2-4 years after completion of the project). Results of this research will be disseminated to growers across the North Central Region through active extension programming. Soybean farmers and the associated agricultural community will benefit from the knowledge that this project will provide, allowing them to adjust agricultural practices to improve or incorporate biological control for more sustainable management of this pest.
Objective 1: Characterize the community of parasitic wasps associated with soybean gall midge.
Objective 2: Evaluate the spatial-temporal dynamics of parasitism of soybean gall midge.
Objective 3: Develop models to identify fields with low or high potential for biological control of soybean gall midge and periods of the growing season when disruptions to fields should be avoided.
Learning outcomes of this project will focus on increasing knowledge of farmers and agricultural professionals about biological control for soybean gall midge. Action outcomes of this project will lead to improved integrated pest management by determining likelihood for biological control across the landscape.
This project addresses the lack of knowledge about the potential for biological control of soybean gall midge (Resseliella maxima [Diptera: Cecidomyiidae]), which is a new pest of soybean in the North Central Region of the U.S. (Gagné et al. 2019). SARE has recognized the importance of biological control to agricultural sustainability and supported such research for other soybean pests (e.g., soybean aphid). SARE has also supported projects focused on other gall midges (e.g., swede midge and orange blossom wheat midge), but not soybean gall midge. Soybean farmers and the associated agricultural community will benefit from the knowledge that this project will provide.
Soybean gall midge larvae feed inside the stems of soybean plants near the soil surface, ultimately causing wilting, lodging, and death of the plants (McMechan et al. 2021). Infestations are typically most severe on field edges with reports of 100% yield losses extending 30 meters into the fields and losses of 17-31% in field interiors (McMechan et al. 2021). At least three overlapping generations of this pest occur per year, with the larvae pupating in the soil (McMechan et al. 2021). Currently, this pest is known to occur in Minnesota, Nebraska, Iowa, South Dakota, and Missouri (McMechan et al. 2021), but its known geographic distribution continues to expand (soybeangallmidge.org). Vast acreages of soybean across the North Central Region may be at risk to infestation by this pest.
Since 2018 when the soybean gall midge first had notable infestations, farmers have had limited, effective management options for this pest. Foliar- and seed-applied insecticides have provided relatively low and inconsistent levels of control for this pest (Hodgson & Helton 2021; McMechan 2021). In addition, varietal resistance (i.e., soybean varieties resistant to the pest) is not available. Therefore, additional management strategies must be explored. Biological control is a cornerstone of integrated pest management (IPM) programs. Parasitic wasps are important biological control agents for other gall midges (Hawkins & Gagné 1989), including the raspberry cane midge (Resseliella theobaldi), which belongs to the same genus as soybean gall midge and has a similar biology (Nilsson 2008, Vétek et al. 2006). Briefly, such parasitic wasps lay their eggs on or inside a host insect (e.g., an egg or larva of a gall midge) and the wasp larvae that hatch from the eggs feed on and kill the host insect. Our recent research in southwest Minnesota, based on rearing and molecular assays of field-collected soybean gall midge larvae, documented for the first time a parasitic wasp associated with soybean gall midge infestations (Koch and Lindsey, unpublished). This parasitic wasp appears to be a new species in the genus Synopeas (Hymenoptera: Platygastridae) (Koch and Lindsey, unpublished). However, it is not uncommon for gall midges to be attacked by multiple species of parasitic wasps (Hawkins & Gagné 1989), so it is possible that there may be other parasitic wasps associated with soybean gall midge.
Research is urgently needed to characterize the community of parasitic wasps attacking soybean gall midge across a broader geography, along with how community structure and parasitism of soybean gall midge vary over time and space. More specifically, biological control of crop pests is influenced by various factors, such as the habitats surrounding crop fields (Landis et al. 2000). Such landscape effects have been shown to affect biological control of pests in soybean in the North Central Region (e.g., Gardiner et al. 2009, Noma et al. 2010) and are likely to occur for soybean gall midge. This project will characterize the community of parasitic wasps attacking the pest and the influences of surrounding habitats which can then be leveraged for development of IPM programs. In particular, these results will enable us to identify areas with high or low potential for biological control. In addition, practices carried out within fields, such as insecticide application and tillage, can also affect biological control (Tooker et al. 2020). The knowledge this project will attain about the seasonal dynamics (phenology) of the parasitic wasps will enable us to determine when disruptions to fields, such as insecticide application or tillage, should be avoided to conserve populations of the parasitic wasps.
Soybean farmers have been and will continue to be involved in the development and implementation of this project. A 2020 survey of Extension clientele (primarily farmers) from three states indicated that biological control should be a priority research area for this pest. Research questions addressed by this project stemmed from discussions with leadership of the MN soybean board, which (through experience with soybean aphid) understands the critical role of biological control in sustainable agriculture. Farmer leaders from the state associations will serve as an advisory committee to ensure continued relevance of the project to agricultural production and assist with dissemination of results and recommendations. In these states, we have established relationships with farmers who have cooperated on other soybean gall midge efforts and are excited to have this team perform research and outreach activities (field days) on their farms. These farmers, like many others, are anxious for guidance on sustainable management of soybean gall midge.
Cooperators
Research
Soybean gall midge will be attacked by a relatively small community of parasitoids (1-3 species).
The community of parasitoids attacking soybean gall midge and the magnitude of their impact (percent parasitism) will vary among field, especially from state-to-state, across the growing season, and in relation to the abundance of soybean gall midge.
The community of parasitoids attacking soybean gall midge and the magnitude of their impact (percent parasitism) will be associated with factors at the landscape level (e.g., amount of crop area vs natural area, etc.) and within field factors (e.g., tillage).
FIELD SAMPLING:
For field sampling in 2023, we identified and sampled a total of 17 soybean fields across four states, with five fields in Minnesota, two fields in South Dakota, five fields in Iowa and five fields in Nebraska. After identifying fields as infested with the soybean gall midge and gaining access to the fields, each field was sampled every two weeks. The number of sample dates per field varied from one to five per field, depending on how early in the season we were able to find and gain access to the fields. Across the states, 14 farmers were involved in this work.
For field sampling in 2024, we identified and sampled a total of 15 soybean fields across four states, with four fields in Minnesota, two fields in South Dakota, four fields in Iowa and five fields in Nebraska. After identifying fields as infested with the soybean gall midge and gaining access to the fields, each field was sampled every two weeks. The number of sample dates per field varied from two to seven per field, depending on how early in the season we were able to find and gain access to the fields. Across the states, 15 farmers were involved in this work.
REARING-BASED ASSESSMENT:
To characterize the community of parasitoids and identify potential new species of parasitoids, sampling was performed in a subset of the above mentioned fields. With this approach, adult parasitoids were reared from field-collected infested plants. This approach enables collection and preservation of insects for morphological and genetic identification. In both years, two of the fields in Minnesota, one of the fields in South Dakota, and two of the fields in Nebraska were also sampled for rearing of parasitoids associated with soybean gall midge. For this effort, on each sample date mentioned above, four sets of ten infested soybean plants were collected from within the same 50 feet of the a field edge. These plants were trimmed and brought to laboratories where they were placed in emergence cages following Melotto et al. (2023). From each collection date from each field, there were four cages with ten stems per cage. The emergence cages were inspected every 1 to 3 days until no further insects emerged from a given cage to collect and preserve emerging adults of soybean gall midge and parasitic wasps. Wasps collected from emergence cages were identified morphologically (confirmed by taxonomist Dr. Elijah Talamas) and genetically.
MOLECULAR-BASED ASSESSMENT:
To quantify parasitism rates, all fields from both years were sampled for molecular-based assessment of parasitism. This molecular approach has been shown to be more sensitive for detection of parasitism in soybean fields than the complementary rearing methods described below (Melotto et al. 2023). On each sample date for a given field, 40 plants were randomly selected and collected from within 50 feet of a field edge, because soybean gall midge shows strong edge effects in its infestation of fields. The stems of the plants were carefully dissected to collect and preserve the soybean gall midge larvae for later quantification of the soybean gall midge larvae and molecular assessment of parasitism. To ensure an adequate number of larvae for assessment of parasitism while balancing costs of staff time, subsetting system was utilized when dissecting the stems. If in the first 10 stems dissected there were 20 larvae in each stem, dissections stopped. If not, then 10 more stems were dissected. If there were 20 larvae in each of those additional 10 stems, then dissections stopped. If not, all 40 stems were dissected. Because more larvae were collected than could possibly be screened, we developed criteria for collecting and processing a representative sample of the larvae from all the infested stems collected from each field. For stems with 0 to 8 larvae, all larvae were processed, and 8 larvae were processed for stems with 9 to 79 larvae, 16 larvae were processed for stems with 80 to 159 larvae, and 32 larvae were processed from stems with 160 or more larvae. This sampling scheme allowed at least 10% of the larvae from each stem to be processed. To determine if larvae were parasitized by Synopeas maximum, established protocols were followed for identifying the DNA of S. maximum in the soybean gall midge larvae (Melotto et al. 2023). However, because an additional species of wasp was detected through this project, we collaborated with taxonomists to identify this species and then developed additional molecular protocols (including development and validation of species-specific primers) to identify and distinguish the DNA of this new wasp species in soybean gall midge larvae. Briefly, DNA was extracted from each larva, and high-throughput qPCR screening was performed using separate primers specific for Synopeas maximum and for the new species of wasp.
REARING-BASED ASSESSMENT:
In 2023, S. maximum was reared from soybean stems collected from four of the five fields sampled (one field from Minnesota, one field from South Dakota and two fields from Nebraska). In addition, a different species of Synopeas (previously undocumented from soybean gall midge) was obtained from emergence cages from the two fields in Nebraska. In these fields in Nebraska, this new species of Synopeas was more abundant than S. maximum.
In 2024, S. maximum was reared from soybean stems collected from two of the five fields sampled (one field from South Dakota and one field from Nebraska). In addition, the other Synopeas species was reared from soybean stems collected from one field in Nebraska. As in the previous year, this other Synopeas species was more abundant than S. maximum in Nebraska.
The additional species of wasp was determined to be Synopeas ruficoxum, which had previously been collected from only a few locations in eastern Canada, but nothing was known about what gall midge species it attacks. By performing molecular assays on subsets of soybean gall midge larvae from fields known to have this wasp, it was confirmed that S. ruficoxum indeed parasitizes soybean gall midge. Because S. ruficoxum is so poorly understood, morphological and molecular data are being used to perform and thorough redescription of this species and to examine its phylogenetic relatedness to other Synopeas species. A scientific paper is currently being drafted in collaboration with two taxonomists (Jess Awad and Elijah Talamas) on this redescription of S. ruficoxum.
MOLECULAR-BASED ASSESSMENT:
Screening for parasitism by S. maximum and S. ruficoxum has been completed for samples from all fields in both years. For S. maximum the highest highest rates of parasitism for a given sample date in 2023 and 2024 were about 10% and 14% for Minnesota, 7% and 0% for Iowa, 14% and 23% for South Dakota, and 22% and 6% for Nebraska. For S. ruficoxum, the highest rates of parasitism for a given sample date in 2023 and 2024 were about 18% and 20% for Minnesota, 3% and 0% for Iowa, 2% and 13% for South Dakota, and 60% and 50% for Nebraska. Across all the states, parasitism by S. maximum appears to be highest late in the season (August-September) and sometimes early in the season (June), whereas parasitism by S. ruficoxum appears to be highest in the middle of the season (July). In the next reporting period, these results from across the region over two years will be thoroughly analyzed to examine potential impacts of within-field and landscape level factors on parasitism rates.
In addition, these data are being analyzed to characterize density dependence of parasitism of soybean gall midge. Preliminary results for S. maximum in 2023 showed that the probability of a soybean plant having parasitism by S. maximum was greater for soybean plants with greater densities of soybean gall midge (P<0.001). For the soybean stems with parasitism, there was evidence for inverse density dependence with parasitism rates decreasing with increasing densities of soybean gall midge (slope from logistic regression=-0.012; P<0.001). The data for parasitism by S. ruficoxum in 2023 and both species in 2024, will soon be analyzed similarly to this. Understanding the nature of the behavior of a parasitoid in relation to host density can provide important insight into the potential for effective and stable control of the pest.
Education
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Project Activities
Educational & Outreach Activities
von Gries, S., A.R.I. Lindsey, E.W. Hodgson, J. McMechan and R.L. Koch. 2024, March. Parasitism of soybean gall midge by Synopeas maximum across the Upper Midwest. Meeting of the North Central Branch of the Entomological Society of America. Fort Collins, CO.
von Gries, S., A.R.I. Lindsey, E.W. Hodgson, A.J. McMechan and R.L. Koch. 2024, November. Unraveling the parasitoid complex of soybean gall midge. 10-minute student competition talk. Meeting of the Entomological Society of America. Phoenix, AZ.
Lisak, S., A.R.I. Lindsey and R.L. Koch. 2023, November. Utilizing qPCR to evaluate soybean gall midge parasitism rates across the Midwest. Meeting of the Entomological Society of America. National Harbor, MD.
Participation Summary:
Extension presentations: The events quantified above were general presentations about soybean gall midge and some included preliminary work on biological control that led to this particular project. However, these were performed before results were collected and/or analyzed from this project.
von Gries, S., A. Lindsey and R.L. Koch. 2025, February. Parasitoids of soybean gall midge. 2025 Midwest Soybean Gall Midge Discussion Series (10-minute presentation with 173 attendees)
Koch, R.L. 2025, February. Updates on soybean gall midge and soybean tentiform leafminer. Best of the Best in Wheat and Soybean. North Dakota State University Extension and University of Minnesota Extension. (30-minute talk; Grand Forks: 115 attendees, Moorhead: 86 attendees)
Koch, R.L. 2025, January. Is agricultural research and extension relevant to high school agricultural teachers? Educators Network Meeting. Turtle Lake, WI (60-minute talk to 9 attendees)
Koch, R.L. 2025, January. Updates on the biology and management of soybean insect pests. Research Updates for Agricultural Professionals, Institute for Agricultural Professionals, University of Minnesota Extension. (50-minute talk; Waseca: 110 attendees, Oronoco: 14 attendees)
Koch, R.L. 2024, December. Updates on management of soybean aphid and soybean gall midge. Crop Pest Management Short Course. Minnesota Crop Production Retailers and University of Minnesota Extension. Minneapolis, MN (two 25-minute talks with 81 and 35 attendees)
Lisak, S., A. Lindsey and R.L. Koch. 2024, April. Biological control for soybean gall midge. 2024 Midwest Soybean Gall Midge Discussion Series (20-minute presentation with 120 attendees)
Lisak, S. and R.L. Koch. 2023, July. Biological control for soybean gall midge. Multistate Soybean Gall Midge Field Day. Mead, Nebraska (20-minute presentation to 105 attendees total)
Koch, R.L. 2023, July. Soybean pest outlook. Strategic Farming: Field Notes (webinar). University of Minnesota Extension (15-minute presentation with 40 attendees & saved as a podcast) https://strategicfarming.transistor.fm/episodes/corn-agronomy-updates-and-preparing-for-soybean-insects
Koch, R.L. 2023, March. Let’s talk old and new soybean insect pests. Strategic Farming: Field Notes (webinar). University of Minnesota Extension (50-minute presentation with 98 attendees & saved as a YouTube video) https://www.youtube.com/watch?v=srH9XWjpy9Q
Koch, R.L. 2023, March. Soybean insects update: soybean aphid, soybean gall midge and soybean tentiform leafminer. Minnesota Winter Region Conference, Winfield United. Mankato, MN (60-minute talk with 200 attendees)
Lisak, S., G. Melotto, B. Potter, A. Lindsey and R.L. Koch. 2023, February. Biological control of soybean gall midge. 2023 Midwest Soybean Gall Midge Discussion Series (15-minute presentation with 230 attendees)
Learning Outcomes
Project Outcomes
2023: This project led to documentation of S. maximum parasitizing soybean gall midge across four states and the detection of an additional parasitoid (a potential new species) attacking soybean gall midge in Nebraska.