Soybean tentiform leafminer in Minnesota soybean

Identification of soybean tentiform leafminer (Macrosaccus morrisella)

Life stages of soybean tentiform leafminer — Fig. 1. Adult (top), larva (middle) and pupae (bottom) of soybean tentiform leafminer. Note the circled adult on quarter for size reference Photos: J. Moisan-De Serres, MAPAQ Québec; Robert Koch, UMN

Adults (Figure 1)

Small moths, about 6-7 mm long
Wings with orange, white and gray-black marks

Larvae (Figure 1)

Small larvae reaching 4.7 mm long
White-colored when young and turn pale-green in color when more mature

Pupae (Figure 1)

Small pupae reaching 3.6 mm long

Natural history

Soybean tentiform leafminer is a native species widely distributed across eastern North America and Canada.

This insect is known to feed on two native plants, American hogpeanut and slickseed fuzzybean, of the Fabaceae family - the same family as soybean. This suggests that the soybean tentiform leafminer has adapted to feed on soybean.

Adults lay eggs on the underside of soybean leaves. Much of the behavior and biology of this insect is still largely unknown.

Impacts

soybean leaves with blotchy mines — Fig. 2. Linear and blotch-type leaf mines caused by soybean tentiform leafminer in a soybean field. Photo: Robert Koch, UMN

Larvae feed inside the leaves and form mines that do not cross the midribs or main lateral veins of the leaves (Figure 2).

Mined tissue eventually dies, so injury from soybean tentiform leafminer reduces leaf area, like defoliation.

On the underside of the leaves, mines start small and linear, but enlarge to elongate-oval, whitish blotches (Figure 3a).

These mines eventually become tentiform - slightly raised or tented - and can be seen on the upper side of the leaves, often with numerous small light-colored spots (Figures 3b).

upper surface of soybean leaf with mines — Fig. 3a. Upper surface of a leaf mine of soybean tentiform leafminer. Photo: Robert Koch, U of MN

lower soybean leaf surface with mines — Fig. 3b. Lower surface of a leaf mine of soybean tentiform leafminer. Photo: Robert Koch, U of MN

Scouting and management

soybean plants infested with mines on the leaves — Fig. 4. Soybean plant heavily infested with mines of soybean tentiform leafminer from a soybean field in southern Minnesota. Photo: Robert Koch, U of MN

Preliminary observations suggest that infestations are heaviest on field edges near wooded areas (Figure 4).

Management decisions for defoliators in soybean are based on estimates of defoliation from the entire canopy (top, middle and bottom levels).

Current defoliation thresholds for soybean:

30% - vegetative states
20% - reproductive stages

Application of foliar insecticides could be an option in the future, but insecticide efficacy and application timing need to be studied for this pest.

Reviewed in 2023