Reports in Canada and Minnesota have documented Macrosaccus morrisella, a native leaf-mining moth species (adult shown here), infesting soybean. While the potential threat the species poses to soybean crops remains to be seen, a new guide in the Journal of Integrated Pest Management profiles the species and alerts growers on what to watch for. (Photo by Joseph Moisan-De Serres)

By Arthur Vieira Ribeiro, Ph.D., and Robert L. Koch, Ph.D.

Robert L. Koch, Ph.D.

Arthur Vieira Ribeiro, Ph.D.

Soybean is an important crop used as food and feed worldwide, and the United States is one of the major producers. A plethora of herbivores, including native and invasive species, colonize and feed on soybean plants. Among this herbivorous community, some species are considered more menacing because they can cause economic damage when in high numbers. As if this community was not large enough already, a native leaf-mining insect, Macrosaccus morrisella, appears to have joined in, expanding its range of host plants to now include soybean, as well.

In a paper published in November in the open-access Journal of Integrated Pest Management—in collaboration with Joseph Moisan-De Serres from the Quebec Ministry of Agriculture, Fisheries, and Food—we provide first reports of this insect feeding on soybean in Canada and the United States. In Québec, Canada, leaf mines were observed over several years and, more recently, also in soybean fields in Minnesota, United States. Heavy infestations with more than 10 mines per leaflet were observed in Québec, while only light infestations with scattered plants showing symptoms were seen in Minnesota.

Macrosaccus morrisella is known to feed on plants of the Fabaceae family, of which soybean is a member. Larvae (such as the one shown here) feed inside the soybean leaves, and the injury—white-colored, blotch-type leaf mines—can be easily detected on the lower surface of the leaves. (Photo by Robert L. Koch, Ph.D.)

Macrosaccus morrisella is known to feed on plants of the Fabaceae family, of which soybean is a member. Larvae feed inside the soybean leaves, and the injury—white-colored, blotch-type leaf mines, as shown here—can be easily detected on the lower surface of the leaves. (Photo by Joseph Moisan-De Serres)

Several small beetles are known to mine the leaves of soybean in North America, but M. morrisella is actually a tiny moth (larvae: 4.7 millimeters long; adults: 6-7 millimeters). Macrosaccus morrisella is known to feed on plants of the Fabaceae family, including American hog peanut. Soybean is a member of this same plant family. Macrosaccus morrisella larvae feed inside the soybean leaves, and the injury—white-colored, blotch-type leaf mines—can be easily detected on the lower surface of the leaves.

The actual damage this new herbivore can cause to soybean production and extent of infestations in soybean fields in North America are still unknown. Next steps should focus on assessing its potential impacts to soybean, geographic extent of infestations of soybean fields, and ecology in agroecosystems. Such information and knowledge on other leaf miners in soybean will help the development of management practices, in case infestations of this new herbivore in soybean increase.

Arthur Vieira Ribeiro, Ph.D. is a postdoctoral associate and Robert L. Koch, Ph.D., is an associate professor and extension entomologist both at the University of Minnesota Department of Entomology. Email: vieir054@umn.edu, koch0125@umn.edu.