Title

Soybean Gall Midge and White-mold Gall Midge in Soybean

(E2006, Dec. 2020)
File
Publication File:
Summary

This publication describes two species of gall midges that infest soybeans. Soybean gall midge is an invasive and economic insect pest of soybeans that occurs in five Midwestern states (Iowa, Minnesota, Missouri, Nebraska and South Dakota). It does not occur in North Dakota yet. The white-mold gall midge is native to North America and is not economic insect pest of soybeans. Larvae of the white-mold gall midge can be found feeding on Sclerotinia white mold disease in stems and pods. This publication describes how to scout and identify the two species based on their location on plants, field symptoms and plant injury symptoms. It also tells pest managers what to do if you find any suspect soybean gall midge in your soybean fields in North Dakota.

Lead Author
Lead Author:
Janet J. Knodel, Professor and Extension Entomologist
Other Authors

Veronica Calles-Torrez, Post-doctoral Scientist; Patrick B. Beauzay, Integrated Pest Management Coordinator and Research Specialist; Alexander H. Knudson, Extension Entomological Diagnostician

Availability
Availability:
Web only
Publication Sections

Table of Contents

Soybean gall midge has not been detected in North Dakota based on our 2019-2020 surveys. A total of 78 fields in 11 counties in 2019 and 605 fields in 47 counties in 2020 were surveyed. Continued monitoring for this pest is crucial to detect its arrival in our state in order to be proactive in its pest management.

During 2019 soybean surveys, the white-mold gall midge was found in Minnesota and North Dakota; however, it is widespread in the northern region of the U.S. This tiny gall midge usually is associated with the fungus Sclerotinia spp., or white mold. The white-mold gall midge is not an insect pest of soybeans, and it primarily has been reported as a white mold fungus feeder.

Figure 1
Photo Credit:
M. Helton, Iowa State University
Adult female (left) and male (right) soybean gall midge
Figure 2
Photo Credit:
J. Moisan-De Serres
Adult white-mold gall midge

Identification

These two gall midges are in the fly family Cecidomyiidae and are similar in appearance. Larval identification of both species is difficult. Larvae easily can be misidentified or confused with larvae of similar gall midge species. Separating the soybean gall midge and white-mold gall midge larvae requires close microscopic examination of their terminal abdominal segments or DNA testing.

Soybean Gall Midge

Young larvae (first and second instars) are white and smaller, whereas the mature third instar larvae (Figure 3) are orange to reddish orange and about 1/12 inch in length. Larvae of soybean gall midge feed on plant liquids by excreting enzymes that digest the plant tissues, sometimes causing galls.

White-mold Gall Midge

Larvae (Figures 4 and 5) are white (first and second instar) to orange (third instar), depending on the age. Larvae are similar in size to soybean gall midge.

Adults of white-mold gall midge (Figure 2) have uniformly grayish antennae, wings and legs with a pale orange abdomen. The white-mold gall midges are similar in size to soybean gall midge adults.

Figure 3
Photo Credit:
V. Calles-Torrez, NDSU
Soybean gall midge larvae in stem
Figure 4
Photo Credit:
J. Moisan-De Serres
White-mold gall midge larvae feeding on white mold-infected stem
Figure 5
Photo Credit:
B. Potter, University of Minnesota Extension
White-mold gall midge larvae feeding on white mold infected pod
Figure 6
Photo Credit:
V. Calles-Torrez, NDSU
Soybean gall midge larval cocoon from soil

Life Cycle

Soybean gall midge likely has two generations per year in northern states. The larva overwinters inside of a larval cocoon (Figure 6) in the soil. Larvae pupate during the spring. The first generation of soybean gall midge adults emerge from mid-June through early July in Minnesota. Adults only live three to five days, and do not feed on soybeans.

Females lay their eggs in crevices or cracks on the soybean stem. Once eggs hatch, larvae begin feeding under the epidermis of the soybean stem and pass through three instars. Numerous larvae sometimes can be found in one soybean stem. Larvae drop off the plant to the soil to form larval cocoons and then pupate. The cycle repeats for the second generation until the fall, when larvae will overwinter as cocoons in the soil.

Crop Damage (Table 1)

Soybean gall midge feeds beneath the epidermis near the base of the stem (Figure 3). Sometimes the base of the stem is necrotic (dark), swollen, deformed and gall-like (Figure 7). Soybean stems heavily infested by soybean gall midge are stunted (Figure 8), wilted, lodged or dead (Figure 9). Significant yield losses have been recorded in states with severe infestations and are most common at the field edges (Figure 9).

Figure 7
Photo Credit:
V. Calles-Torrez, NDSU
Dark discolorations from soybean gall midge feeding injury at the base of soybean stems
Figure 8
Photo Credit:
V. Calles-Torrez, NDSU
Stunted plants from soybean gall midge damage
Figure 9
Photo Credit:
J. McMechan, University of Nebraska
Dead soybeans from soybean gall midge infestation near field edges

The white-mold gall midge feeds on Sclerotinia species on and within infected stems, pods and other tissues (Figures 4 and 5). This species of gall midge can be found anywhere in the field where soybean plants are infected with Sclerotinia white mold fungus (Figures 10 and 11). White-mold gall midge also has been identified in other crops that are susceptible to Sclerotinia white mold fungus, such as canola, dry beans, potatoes and sunflowers.

Figure 10
Photo Credit:
V. Calles-Torrez, NDSU
Soybean infected with Sclerotinia white mold
Figure 11
Photo Credit:
V. Calles-Torrez, NDSU
Soybean field with severe Sclerotinia white mold. Notice the dead plants in the middle of the field.

Because this insect does not feed directly on vegetative or reproductive tissues of soybeans, and predominantly feeds on the white mold, growers do not need to control the white-mold gall midge. However, growers should consider managing severe white mold infections in their fields.

Table 1. Comparison between soybean gall midge and white-mold gall midge: color of larvae, location of larva in field
and on plants, plant injury symptoms, and soybean yield impact.

DescriptionSoybean gall midge (R. maxima)White-mold gall midge (K. caulicola)
Color of larvaWhite to reddish-orangeWhite to orange (often light orange)
When larvae are observed in fieldAs early as V2 (2nd leaf stage) of soybean
(in states with severe infestations)		Later in season, after flowering and onset of Sclerotinia white mold infections
Location of larvae in fieldField edges, especially soybean fields near previous year’s soybeanThroughout the field where Sclerotinia white mold is present
Where larvae are located
on soybean plant		Under epidermis of stem, at or near base of plant, or higher up on stem later in seasonAnywhere on/in Sclerotinia-infected stems and pods
Plant injury symptomsNecrotic, brown or dark discolorations at the base of plant, some plants with swollen stems. Plants easily broken off at base. Lodging, wilting and dead plants.

None for insect.

Disease Symptoms: Stems or pods infested with Sclerotinia, presence of mycelium in stems and on vegetative tissues, dead plants with mycelium.

Yield impactBecause of stunted, dead plants, small pods/seeds, and reduced plant stand, yield can be reduced from 20 to 100%, especially on field edges with heavy infestation.None. This insect does not cause yield loss. However, Sclerotinia white mold can cause significant yield loss if not managed.

Field Scouting (Table 1)

Soybean Gall Midge

Adults are not readily observable in the field due to their cryptic appearance, small size and short life span. Larval-infested stems are easier to find near the field edges of soybeans (Figure 9) or in newly planted soybean fields that are close to last year’s infested fields, and during the R2 (full bloom) to R8 (maturity) growth stages of soybeans.

Scout by walking a transect in the first four rows near the field edge and focus in areas where dense vegetation occurs along the field edge. Examine 10 consecutive plants at 10 sampling sites per field (total of 100 plants per field). Sampling sites should be spaced more than 50 feet apart.

At each sampling site, examine plants for the presence of necrosis and brown or dark discoloration at the base and lower portion of each stem (Figure 7). If necrosis is observed, pull up the soybean plant and peel back the outermost layer of the stem (epidermis) on the necrotic area to look for small white or orange larvae.

Growers are encouraged to scout for soybean gall midge. Additional scouting will help detect this economic insect pest of soybeans and determine if or when it becomes established in North Dakota.

White-mold Gall Midge

To find the white-mold gall midge in soybean fields, you can look for white mold-infected soybean plants, which have white cottony mycelium on the stems, pods and leaves, bleached or dead stems, or dying soybean patches in the field.

If white mold is observed on plants, pull up a few plants and examine for the presence of white to orange larvae in or on infected soybean tissue and mold. If larvae are found directly associated with white mold, then they are most probably the white-mold gall midge.

What to Do if You Find Suspect Soybean Gall Midge in North Dakota

If you happen to find white or orange larvae in the stems of soybeans, you need to confirm whether it is the soybean gall midge or white-mold gall midge. Collect more than 10 larvae and place them in alcohol vials, or collect two to three plants with larvae and place them in a plastic bag. Send collected samples to the Extension agent in your county or to NDSU Extension Entomology for further identification.

Integrated Pest Management (IPM) of Soybean Gall Midge

Because the soybean gall midge is a newly discovered insect pest, entomologists have been studying different integrated pest management strategies. Studies on planting dates, crop rotation, tillage and insecticide control for this pest are being conducted in states with severe infestations.

Other Resources

Gagné, R. J., J. Yukawa, A. K. Elsayed, and A. J. McMechan. 2019. A new pest species of Resseliella (Diptera: Cecidomyiidae) on soybean (Fabaceae) in North America, with a description of the genus. Proc. Entomol. Soc. Wash. 121: 168–177.

Koch, R. L., J. Kurle, D. Malvick, and B. D. Potter. 2019. Soybean gall midge not only small orange fly larvae in Minnesota soybean fields: another species associated with white mold. University of Minnesota Extension. Available at: https://blog-crop-news.extension.umn.edu/2019/10/soybean-gall-midge-not-only-small.html

Koch, R. L., B. D. Potter, J. Moisan-De Serres, J. Knodel, V. Calles-Torrez, J. Gavloski, T. Cira, M. Bartz, and R. Gagné. 2020. Karshomyia caulicola (Diptera: Cecidomyiidae) associated with Sclerotinia-infected soybean in the United State and Canada. The Great Lakes Entomologist 53: 58–62.

McMechan, J., T. Hunt, and R. Wright. 2018. Soybean gall midge: adult stage identified. University of Nebraska–Lincoln. Available at:
https://cropwatch.unl.edu/2018/soybean-gall-midge-adult-stage-identified

Potter, B. and B. D. Potter. 2019. Soybean gall midge in Minnesota soybean. University of Minnesota Extension. Available at:
https://extension.umn.edu/soybean-pest-management/soybean-gall-midge-minnesota-soybean

Published with support from the North Dakota Soybean Council, North Central Soybean Research Program, and the USDA National Institute of Food and Agriculture, Hatch project accession no. 1018411, and the Crop Protection and Pest Management grant no. 2017-70006-27144.