The soybean tentiform leafminer is a native insect that has recently developed the ability to feed on soybean. The levels of leaf injury caused by this pest are alarming and could threaten soybean yields. Therefore, urgent work is needed to evaluate potential control methods for this pest. The work proposed here is the second year of a three-year project focused on evaluating control methods that could be used to respond to this pest. First, certain insecticides with translaminar activity (ability to move through leaves) proved effective at controlling this pest in the first year of this project. Further work is needed in this second year to evaluate additional insecticides, particularly those with the ability to move through leaves to contact the insects inside the mines. This field efficacy trial will be performed in the field of a cooperating farmer. Second, leafmining insects are generally attacked and killed by multiple parasitic wasps, and our preliminary work has found that the soybean tentiform leafminer is attacked by several species of parasitic wasps. However, further work is needed in this second year to characterize the community of parasitic wasps attacking this pest and quantify the levels of mortality they inflict on the pest populations. Results of this proposed work will allow us to develop integrated pest management recommendations including chemical and biological controls for this pest.

1. GOAL: To build the foundation for the development of management programs for soybean tentiform leafminer, we propose the following goals and objectives:
OBJECTIVES:
1. Evaluate the efficacy of insecticides against soybean tentiform leafminer in soybean fields
2. Assess diversity and impacts of parasitic wasps attacking soybean tentiform leafminer populations

This project will provide several important deliverables that will advance management programs for
soybean tentiform leafminer in Minnesota. This project will produce foundational knowledge on
chemical and biological control against this pest. This knowledge will help farmers determine which
insecticides to use against this pest and if natural control provided by parasitic wasps can help suppress
infestations. This knowledge will be housed on the UMN Extension website and made widely available
to farmers and the agricultural community through our extension programming (see communication
plan above) and through the communication channels of Minnesota Soybean. Finally, this project will
facilitate the continued training of post-doctoral in Entomology, who will gain expertise in pest ecology
and integrated pest management.

Updated August 30, 2024:
Reporting period: 1 May 2024 to 30 July 2024

Proposal Objectives & Goal Statements:
To build the foundation for the development of management programs for soybean tentiform leafminer (STL), we propose the following goals and objectives:
Goal 1: Evaluate the efficacy of insecticides against soybean tentiform leafminer in soybean fields
Goal 2: Assess diversity and impacts of parasitic wasps attacking soybean tentiform leafminer populations

Specific project achievements during this reporting period:
Goal 1:
For the field insecticide efficacy experiment, we identified a soybean field with an STL infestation in south-central Minnesota and attained permission to perform this work. Research plots have been established in a randomized complete block design. Preparations are being made to apply insecticides to the plots in August.
Goal 2:
To characterize the community of parasitic wasps attacking STL and the magnitude of their impact on this pest, we identified two soybean fields with nearby wooded areas containing hogpeanut. These fields are located on the St. Paul Campus of the UMN and on a farm in south-central Minnesota. Since early vegetative growth stages of the soybean plants, the soybean and hogpeanut plants have been sampled to quantify the level of STL infestation and to collect infested plant tissue for rearing of parasitic wasps in the laboratory. The wasps emerging from infested plant tissue in the laboratory are being preserved for later identification. The communities of parasitoids and their impacts on the pest will be compared between plant types and locations.

Challenges encountered
No problems occurred during this period

Dissemination of data/information during this reporting period
Results of this work will be disseminated to stakeholders in winter extension meetings.

Updated November 25, 2024:
Reporting period: 1 August 2024 to 31 October 2024

Proposal Objectives & Goal Statements:
To build the foundation for the development of management programs for soybean tentiform leafminer (STL), we propose the following goals and objectives:
Goal 1: Evaluate the efficacy of insecticides against soybean tentiform leafminer in soybean fields
Goal 2: Assess diversity and impacts of parasitic wasps attacking soybean tentiform leafminer populations

Specific project achievements during this reporting period:

Goal 1:
A field insecticide efficacy experiment was performed in an infested soybean field on a farm near Henderson, MN. Research plots were established in a randomized complete block design parallel to the edge of the field to account for this insect’s strong edge effect in infestations. The plots were sprayed with insecticides on August 19 and leaves were collected after 1, 2 and 3 weeks to compare the leaf area mined (injured) and survival of larvae in the leaf mines in the plots treated with the various treatments (insecticides and untreated control). Data from this experiment will be summarized and analyzed in the next reporting period.

Goal 2:
To characterize the community of parasitic wasps attacking STL and the magnitude of their impact on this pest, we sampled two soybean fields and corresponding nearby wooded areas containing hogpeanut. These fields and wooded areas were located in St. Paul and on a farm near Henderson. Sampling began during early vegetative growth stages of the soybean plants and continued through plant maturity. On each sample date, we collected infested soybean and hogpeanut leaves to quantify the level of STL infestation and to rear insects (adult STL and parasitic wasps) from the infested leaves in the laboratory. The wasps that emerged from infested plant tissue in the laboratory were preserved and will be identified in the next reporting period. The resulting data will be analyzed in a future reporting period, to compare the communities of parasitic wasps and their impacts on the pest between plant types and locations.

Challenges encountered
No problems occurred during this period

Dissemination of data/information during this reporting period
Results of this work will be disseminated to stakeholders in winter extension meetings.

Updated February 22, 2025:
Reporting period: 1 November 2024 to 30 January 2025

Proposal Objectives & Goal Statements:
To build the foundation for the development of management programs for soybean tentiform leafminer (STL), we propose the following goals and objectives:
Goal 1: Evaluate the efficacy of insecticides against soybean tentiform leafminer in soybean fields
Goal 2: Assess diversity and impacts of parasitic wasps attacking soybean tentiform leafminer populations

Specific project achievements during this reporting period:
Goal 1:
A field insecticide efficacy experiment was performed in an infested soybean field on a farm near Henderson, MN. Research plots were established in a randomized complete block design parallel to the edge of the field to account for this insect’s strong edge effect in infestations. The plots were sprayed with insecticides on August 19 and leaves were collected after 1, 2 and 3 weeks to compare the leaf area mined (injured) and survival of larvae in the leaf mines in the plots treated with the various treatments (insecticides and untreated control). Overall infestation levels from this pest were low, which resulted in less than 3% of leaf area mined, and there were no differences among the treatments.

Goal 2:
To characterize the community of parasitic wasps attacking STL and the magnitude of their impact on this pest, we sampled two soybean fields and corresponding nearby wooded areas containing hogpeanut. These fields and wooded areas were located in St. Paul and on a farm near Henderson. Sampling began during early vegetative growth stages of the soybean plants and continued through plant maturity. On each sample date, we collected infested soybean and hogpeanut leaves to quantify the level of STL infestation and to rear insects (adult STL and parasitic wasps) from the infested leaves in the laboratory. The wasps that emerged from infested plant tissue in the laboratory were preserved and have all been identified to genus or species levels. Identification of these tiny wasps was a very time-consuming and challenging process. Across the two years, about 20 species of parasitic wasps have been found association with this pest. These data will be analyzed during the next reporting period to examine if communities of parasitic wasps and their resulting levels of parasitism differs between soybean plants in fields and the native host in wood areas.

Challenges encountered
No problems occurred during this period

Dissemination of data/information during this reporting period
Results of this work has been disseminated to stakeholders in winter extension meetings, including:
-Koch, R.L. 2025, February. Soybean insect issues and Extension programming for agricultural professionals. Annual Meeting of the Minnesota Independent Crop Consulting Association, St. Cloud, MN (20-minute talk with 55 attendees)
-Koch, R.L. 2025, February. Updates on soybean gall midge and soybean tentiform leafminer. Best of the Best in Wheat and Soybean. North Dakota State University Extension and University of Minnesota Extension. (30-minute talk; Grand Forks: 115 attendees, Moorhead: 86 attendees)
-Koch, R.L., P. Anderson and A. Ribeiro. 2025, January. Advances in soybean entomology research. Poster presentation. Minnesota Ag Expo, Mankato, MN
-Koch, R.L. 2025, January. Updates on the biology and management of soybean insect pests. Research Updates for Agricultural Professionals, Institute for Agricultural Professionals, University of Minnesota Extension. (50-minute talk; Waseca: 110 attendees, Oronoco: 14 attendees)

Updated May 31, 2025:
Final report: May 2025

Proposal Objectives & Goal Statements:
To build the foundation for the development of management programs for soybean tentiform leafminer (STL), we propose the following goals and objectives:
Goal 1: Evaluate the efficacy of insecticides against soybean tentiform leafminer in soybean fields
Goal 2: Assess diversity and impacts of parasitic wasps attacking soybean tentiform leafminer populations

Specific project achievements during this reporting period:
Goal 1:
Insecticides are an important tool for the initial (emergency) response to new insect pests. A field insecticide efficacy experiment was performed in an infested soybean field on a farm near Henderson, MN. Research plots were established in a randomized complete block design parallel to the edge of the field to account for this insect’s strong edge effect in infestations. Endigo and AgriMek, which have translaminar properties and showed promise for control of this pest the previous year, were further evaluated in this study. The plots were sprayed on August 19 and leaves were collected after 1, 2 and 3 weeks to compare the leaf area mined (injured) and survival of larvae in the leaf mines in the plots treated with the various treatments (insecticides and untreated control). Overall infestation levels from this pest were low, which resulted in less than 3% of leaf area mined. More leaf area was mined in the lower canopy compared to upper canopy; however, there were no differences in leaf area mined among the insecticide treatments or untreated.

Goal 2:
Biological control is a foundational component of integrated pest management programs. To characterize the community of parasitic wasps attacking STL and the magnitude of their impact on this pest, we sampled two soybean fields and corresponding nearby wooded areas containing hogpeanut. These fields and wooded areas were located in St. Paul and on a farm near Henderson. Sampling began during early vegetative growth stages of the soybean plants and continued through plant maturity. On each sample date, we collected infested soybean and hogpeanut leaves to quantify the level of STL infestation and to rear insects (adult STL and parasitic wasps) from the infested leaves in the laboratory. The wasps that emerged from infested plant tissue in the laboratory were preserved and have all been identified to genus or species levels. This project was complemented by funding secured from RARF which allowed sampling of soybean and hogpeanut at additional locations spread across Minnesota, but less intensively (only two sample dates) at these additional sites. We collaborated with a taxonomist specialized in these types of wasps to perform morphological identifications of the many tiny wasps reared from our samples. This challenging, time-consuming task has been completed. Nearly 20 species of parasitic wasps have been found to attack this pest. The scientific literature on these various species is being checked to confirm which species have been previously reported attacking related leafmining insects (Gracillariidae) versus those that might have been attacking stray aphids or other insects in our samples. In addition, these data are being analyzed and summarized to compare the communities of parasitic wasps and their resulting levels of parasitism between soybean and hogpeanut and across the state.

Challenges encountered
Over the course of this project, the only major challenge was the low level of insect pest pressure in the insecticide efficacy study. However, data from the previous year and complementary laboratory and greenhouse studies show the potential for translaminar insecticides (e.g., Endigo) to control this pest.

Dissemination of data/information during this reporting period
Results of this work have been disseminated to stakeholders through extension meetings reported on in previous progress reports. Recently, two interviews were conducted that will share results of this project (and complementary projects funded by other sources) through the Soybean Research and Information Network and the podcast called I See Dead Plants. Furthermore, a new MN Crop News article is being prepared to summarize these results for farmers and ag professionals in Minnesota.

The soybean tentiform leafminer (STL) has emerged as a new pest of Midwest soybean. This research was aimed at providing a foundation for development of an integrated pest management program for this pest. Two important management tactics were examined: chemical control and biological control.
A field insecticide efficacy experiment was performed in an infested soybean field on a farm near Henderson, MN. Endigo and AgriMek, which have translaminar properties and showed promise for control of this pest the previous year, were further evaluated in this study. Overall infestation levels from this pest were low, which resulted in less than 3% of leaf area mined. More leaf area was mined in the lower canopy compared to upper canopy; however, there were no differences in leaf area mined among the insecticide treatments or untreated. However, data from the previous year and complementary laboratory and greenhouse studies show the potential for translaminar insecticides (e.g., Endigo) to control this pest.
Field sampling was performed over the season at two locations in Minnesota to characterize the community of parasitic wasps attacking STL and the magnitude of their impact on this pest in soybean fields and corresponding nearby wooded areas containing hogpeanut. Plant samples from soybean and hogpeanut brought to the laboratory to quantify the level of STL infestation and to rear insects (adult STL and parasitic wasps). Nearly 20 species of parasitic wasps have been found to attack this pest. These data are being analyzed and summarized to compare the communities of parasitic wasps and their resulting levels of parasitism between soybean and hogpeanut and across the state.

Soybean tentiform leafminer is a new pest that poses a threat to soybean production. Currently,
knowledge about this pest in soybean is limited and little is known about potential management tactics.
This limits the ability of farmers to prepare for and respond to the pest. Investment in this project will
enable us to provide recommendations to inform farmers about how to effectively manage this pest.
More specifically, recommendations for chemical and biological controls will be generated to help the
farmers protect their crops.