Timing of adult emergence from the soil varies by geography with first adult emergence observed in mid-June in Nebraska and early July in Minnesota (Knodel, 2019). Adults have a long emergence window – overwintering generation adult emergence extended over a 17-day period in a Corteva Agriscience study in 2019 and as long as 37 days in a 2021 study (Figure 10). Adults live three to five days and do not feed on soybean plants (Calles-Torrez et al., 2020).
Females lay eggs in cracks and fissures in soybean stems. Females do not pierce the stem tissue when laying eggs. Larval infestation of soybean plants has not been observed prior of the V2-V3 growth stage. At this stage of soybean growth, the stem diameter expands creating small fissures allowing the overwintering generation adults to deposit eggs into the stem (McMechan et al., 2021c). Prior to V3, the soybean stems do not have these fissures.
Newly hatched larvae feed under the epidermis of the stem and go through three instars. Larvae drop off the plant to the soil, where they form larval cocoons and pupate (Calles-Torrez et al., 2020). Adults then emerge and repeat the cycle. Adults are not strong fliers, so are limited in their mobility. The effect of wind in dispersing adults over longer distances is under investigation.
Based on observations so far, soybean gall midge appears to go through two or three overlapping generations per season. The substantial overlap between generations makes it difficult to detect discrete generations within the growing season, and larvae can be present in an infested field continually over the majority of the growing season. The timing of adult emergence cessation in the fall appears to be relatively consistent from year to year (McMechan et al., 2021a).
Research on soybean gall midge lifecycle has been challenging due to the fact that entomologists have not yet been able to sustain a colony in a laboratory environment. What is known about the insect’s lifecycle so far comes entirely from field observations. Consequently, many aspects of the soybean gall midge lifecycle have been difficult to ascertain or remain unknown. Basic facts such has generation time, number of eggs laid by females, favorable conditions for development, and characteristics that drive host plant selection are all important for formulating a management plan but remain poorly understood.