Project Details:

Soybean Gall Midge: Surveying the North Central Region, Adult Monitoring and Host Plant Resistance

Parent Project: Soybean Gall Midge: Identifying management opportunities for an emerging pest of soybeans
Checkoff Organization:North Central Soybean Research Program
Categories:Insects and pests
Organization Project Code:26-6228-0327-001
Project Year:2020
Lead Principal Investigator:Justin McMechan (University of Nebraska)
Co-Principal Investigators:

Contributing Organizations

Funding Institutions

Information and Results

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Project Summary

In late June 2018, entomologists in Iowa, Nebraska, and South Dakota received reports of soybean fields with visible signs of dead or dying plants found to be associated with an infestation of cecidomyiid larvae at the base of the stem (Hodgson 2018; McMechan et al. 2018a; Varenhorst 2018). Field surveys were initiated in these three states as well as Minnesota to determine the distribution and extent of the damage. Results found midge larvae were present in 65 counties across the four states. Due to the widespread nature of the damage, significant efforts were made to identify the species. In early August, the adult stage of this insect was captured from field emergence cages and reared in a growth chamber through a single generation. These adults along with larvae were sent to two leading taxonomic authorities on cecidomyiidae. Morphological and genetic comparisons with known species in the genus Resseliella led to the conclusion this cecidomyiid midge is a new species, Resseliella maxima (Gagne et al. 2019). The name maxima was chosen because of the host, Glycine max, and the potential damage that this insect can cause to soybean. This is the first report of a species in the genus Resseliella on soybean in North America. The widespread damage associated with this pest and its identification as a new species has left researchers and farmers with significant gaps in knowledge that need to be addressed to develop a viable integrated pest management program.

Although soybean gall midge was recently identified and designated as a significant pest of soybean, it is not new to the North Central region. The larval stage of gall midge was found in isolated soybean fields in 2011 in northeast Nebraska (Hunt et al. 2011). These fields had received hail damage during the early half of the growing season, and it was thought that the adult midges were attracted to lay eggs on the damaged plants and that the larvae were feeding on the decaying or already damaged tissue. Similar reports occurred in late-August of 2015 in South Dakota that were associated with similar extreme weather events (hail, wind and rain) (Varenhorst and Strunk 2015). A number of these plants were infected with diseases such as stem canker, charcoal rot, pod and stem blight, cercospora leaf blight, and brown spot on infested plants. Initial observations in South Dakota suggested that the larvae were feeding on a fungus that was present under the epidermis. Soybean gall midge was observed in 2016 and 2017 in east central Nebraska but these reports, including those from previous years, were all confined to mid- to late-August. Late season infestations of gall midge raised little concerns over potential yield losses, and it was assumed that other factors such as plant damage or disease were the leading cause.

In 2018, yield losses from soybean gall midge were most extensive at the field edge. Soybean plants infested with soybean gall midge often had darkened tissue or swollen stems near the soil surface. Peeling back this tissue would expose the immature stages of the gall midge feeding within and at the leading edge of the darkened areas on the stem. In October, soybean plants were hand-harvested from a heavily damaged field in Saunders County, NE. Samples of ten linear feet of row were harvested at 1, 10, 20, 50, 100, 200 and 400 feet from the field edge. Soybean yield losses were greater than 92% for the first 100 feet from the field edge with 31% and 20% yield losses at 200 and 400 feet from the field edge. Roundtable discussions with 85 stakeholders after harvest found an average yield loss of 78% for the first 100 feet and 17% on the remainder of the field. Some of these participants indicated they had made insecticide applications in the spring of 2018 to mitigate pest pressure but had little success. Reduced efficacy with insecticides could be due to a number of factors, however, the primary factor is a likely a lack of information on the timing of adult gall midge movement in the spring.

Emergency funding from the North Central Soybean Research Program has provided researchers in Nebraska, Iowa, South Dakota and Minnesota with the resources to track soybean gall midge emergence in the spring of 2019. Farmers are taking advantage of this effort and implementing border spray applications, tillage treatments and mowing vegetation around the field in an effort to mitigate losses. Preliminary management practices have focused almost exclusively on insecticides to mitigate pest pressure. The efficacy of these products and the window of opportunity to apply them is largely unknown. In addition, relying on pesticides as a pest management program may lead to secondary pest issues or resistance to insecticides by soybean gall midge. To date, no commercial soybean varieties have been identified as resistant to soybean gall midge. Roundtable discussions found that a number of stakeholder suspected a particular variety had resistance but such situations were likely a result of other factors since the same soybean variety was found to be susceptible at another location.

Evaluating soybean lines for resistance is an essential component for a pest management program. A successful screening process would greatly reduce the number of insecticide applications, limiting issues with secondary pests and soybean gall midge developing insecticidal resistance.

Stakeholders have been actively engaged since soybean gall midge emerged as a significant pest through roundtable discussions, on-farm research and extension presentations. To document their need for soybean gall midge research, a petition was developed and distributed at these events. To date, signatures have been obtained from 367 individuals across 33 Nebraska counties. A number of these counties are outside of areas where soybean gall midge has been documented.

Project Objectives

1) Determine the distribution and severity of soybean gall midge across the North Central region.
2) Determine the emergence timing and source of soybean gall midge.
3) Screen soybean varieties for resistance or tolerance to soybean gall midge.
4) Disseminate information to stakeholders on current information and management for soybean gall midge.

Project Deliverables

- Provide a map of soybean gall midge distributions and its damage to soybean in the North Central region.
- Increase awareness of soybean gall midge and reduce the likelihood of unexpected losses.
- Create a platform to share current research on soybean gall midge with researchers and stakeholders across the region.
- Mobilize resource and direct efforts in areas with pressure or presence of soybean gall midge.
- Provide stakeholders with a resource to make management decisions on soybean gall midge.
- Increase return on investment of short-term control strategies (i.e., insecticides).
- Develop adult soybean gall emergence model to aid in making future management decisions.
- Learn if soybeans display variable reaction to soybean gall midge infestation.
- Identify any soybean genotypes or lines with resistance or tolerance to soybean gall midge.
- Map genomic regions in soybean associated with reaction to soybean gall midge.
- Potentially identify putative resistance genes.
- Depending on the level of resistance, preliminary information on the yield of lines under significant insect pressure vs. non-infested yield levels will be obtained.
- Disseminate information on resistance/susceptibility reaction and mapped genomic regions so public and commercial breeding programs can screen their germplasm for alleles that confer resistance to soybean gall midge, and use that information to facilitate more rapid identification and development of elite, resistant soybean cultivars.
- Understand if/what follow-up is needed to fully characterize reaction to soybean gall midge.
- Increase stakeholder awareness and understanding of soybean gall midge through publications and field guides.
- Engage and maintain dialogue with stakeholders to identify barriers to adoption or implementation of management recommendations for soybean gall midge.

Progress of Work

Updated April 19, 2020:
- Surveys on the distribution and severity of soybean gall midge were projected to occur in July and August of 2020. The ability to deliver on this objective has become increasingly difficult as a result of the Covid-19. Some state universities (SDSU, Ohio State, Michigan) have indicated significant travel restrictions or a complete lockdown of field research or surveys in during the 2020. Other states within the region are able to function but with a reduction in personnel due to a hiring freeze or limitations in travel. A meeting has been scheduled for May 5th to update collaborators on the latest soybean gall midge information and obtain information from states on the ability to deliver on objectives with restrictions under the Covid-19 pandemic.
- In east-central Nebraska, early emergence cages were placed on March 1st at three locations to track the potential for early emergence. Minnesota and Iowa will deploy cages on May 1st. In Nebraska and Iowa, additional steps were taken to collect soil samples from infested field and extract larvae using a brine extraction method. This method will be overlaid with the emergence cage network in these states to see if the accuracy or likelihood of adult capture can be increased through the detection of larvae in soil samples. In east-central Nebraska, a total of 14 sites have been samples for the presence of larvae and will be monitoring in 2020 for adult emergence.
- Seeds have been prepared for planting for the germplasm screening objective. The tests include 768 diverse soybean germplasm accessions from the USDA Soybean Germplasm Collection and 166 elite, high-yield entries from the University of Nebraska soybean breeding program. The 768 germplasm entries represent the genetic diversity present in the entire collection of ~20,000 accessions. For 2020 planting, the germplasm set will be evaluated in four replications of an augmented incomplete block design at two infested locations in Nebraska and one Iowa location. The set of elite lines will be evaluated in two reps at each of the two Nebraska locations. So for the three locations of germplasm tests, that is a total of 9,216 plots, and 664 plots for the elite lines. We anticipate planting during the first week of May.
- Significant extension efforts have been made to educate and promote this value of this program to clientele. Over the past 6-months, a total of approximately 63 presentations and 6 extension articles have been given or written across several states to make clientele aware of the progress and the tools that they will have for making decisions in 2020. In addition, the alert network has increased the number of registered clientele by 21% since October of 2019. A round table was also held at the Eastern Nebraska Research and Extension Center with 93 participants who rated soybean gall midge ecology and the identification of host plant resistance as their top priorities that they would like to see researchers focus on. In addition, a total of 44 research opportunity forms were filled out, indicating their interest in participating in on-farm research projects on soybean gall midge.

Final Project Results

Benefit to Soybean Farmers

Soybean farmers will benefit from knowing whether or not soybean gall midge is in their area through a systematic survey. The detection of gall midge in a new area can allow for researchers to take early steps to mitigate potential production losses and information can be mobilized and delivered through extension to help with management.

For farmers in heavily impacted areas, the soybean gall midge adult emergence network provides farmers with critical information necessary for initiating management practices to mitigate losses for soybean gall midge.

If host plant resistance is found for soybean gall midge it would provide growers with a much needed foundation for managing soybean gall midge. The discovery of a resistant line to soybean gall midge would also allow for a reduction in insecticide use. In turn this would lead to a reduction in likelihood for a surge of secondary pests that can happen with early season insecticide applications.

The development of short summaries and handouts for farmers will increase awareness of gall midge and provide growers with a concise summary of the information available about the pest and potential management strategies.

Performance Metrics

Project Years