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Gall Midges in Soybeans (09/10/20)

Some inquiries have come in concerning gall midges in soybeans over the past three weeks and whether it is the ‘soybean gall midge’ pest.

Some inquiries have come in concerning gall midges in soybeans over the past three weeks and whether it is the ‘soybean gall midge’ pest. There are two gall midges (Family Cecidomyiidae) that infest soybean, and can be found inside stems of soybean:  soybean gall midge (SGM) and white mold gall midge.

Soybean gall midge, Resseliella maxima Gagné, is a new economic insect pest of soybeans, which is decreasing yields especially along field edges. It has been confirmed in five states including Nebraska, South Dakota, Iowa and Missouri, but not confirmed in North Dakota yet. This year, SGM was severe in Nebraska (see Figure below of dead plants near field edge) but less problematic in Iowa and South Dakota. Larvae are very small, white when young and turn to a reddish-orange when mature.

White mold gall midge, Karshomyia caulicola Coquillett, is associated with white mold (Sclerotinia sclerotiorum) in the stems of soybean, dry beans, canola, sunflowers, potatoes and other crops that get infected with white mold in ND. Larvae feed only on the white mold fungus, but look just like SGM larvae to the ‘eye’ in the field. White mold gall midge is not injurious to soybean and can be fairly widespread in ND and MN, if Sclerotinia is present.

In Table 1, the general field characteristics of the two species of gall midge are compared (Source: R. Koch, UMN). However, larva of the two species can only be separated and identified by DNA testing or detailed microscopic examination of larval integument, terminal abdominal segment, and spatula. If you find some orange larvae in the stems of soybeans that you would like identified as SGM, please collect >10 larvae, place into an alcohol vial and send to Dr. Knodel or your local county extension agent.

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Janet J. Knodel

Extension Entomologist

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