This project addresses a priority item listed under the category of Soybean Pest Management in the FY2023 request for proposals: ”Soybean farmers need continued research into cultural, chemical and biological control mechanisms for management of soybean insects including, but not limited to, soybean aphid, Japanese beetle and soybean gall midge.”

Macrosaccus morrisella (sometimes called the soybean tentiform leafminer) is a tiny moth native to North America. It was found attacking soybean in the United States for the first time in 2021 (Koch et al. 2021). The immature stage (larva) of this moth lives and feeds inside leaves (Davis and De Prins 2011), leading to loss of functional leaf area (i.e., defoliation). In 2022, M. morrisella was found infesting soybean across a broad area of southern Minnesota and eastern South Dakota, with some infestations causing up to 40% defoliation in parts of fields (Koch, unpublished data). Such levels of defoliation by insect pests can significantly decrease soybean yield (Owen et al. 2013).

The appearance of a leaf-mining insect like M. morrisella in Midwest soybean is a significant concern, especially because other leaf-mining moths are significant pests of soybean in other places, like the leaf-mining moth Aproaerema modicella in Africa, Asia, and Australia (Gaur and Mogalapu 2018, Buthelezi et al. 2021). Furthermore, the leaf-mining moth M. robiniella, a related species of M. morrisella, is a significant pest of ornamental plants in Europe (Davis and De Prins 2011). Thus, research is urgently needed to assess the potential impacts of M. morrisella and how to manage its infestations. Unfortunately, there is only limited knowledge on M. morrisella in the forest systems where it historically occurred in Eastern North America (Davis and De Prins 2011) and even less knowledge about it in soybean (Koch et al. 2021).

To build the foundation for the development of management programs for M. morrisella, we propose the following goals and objectives:

Goal 1: Assess the effectiveness of insecticides for management of M. morrisella

• Objective 1: Evaluate the toxicity of insecticides against adults of M. morrisella in the laboratory
• Objective 2: Evaluate the efficacy of insecticides against M. morrisella in soybean fields

Goal 2: Assess host preference and varietal resistance of soybean to M. morrisella

• Objective 1: Determine host preference and varietal resistance of two native plants and several soybean varieties for M. morrisella
• Objective 2: Characterize relationship between abundance of M. morrisella in soybean fields and in native plants in wooded areas in close proximity

This project will provide several important deliverables that will advance M. morrisella management in Minnesota. This project will produce foundational knowledge on the chemical control, host preference and varietal resistance of soybean against M. morrisella. This knowledge will improve the general understanding of the biology of this pest and establish the foundation for the development of management. This knowledge will be housed on the UMN Extension website and made widely available to farmers and the agricultural community through our extension programming and through the communication channels of Minnesota Soybean. Finally, this project will facilitate the training of an undergraduate student in Entomology, who will gain expertise in pest ecology and integrated pest management.

Update:
Goal 1: Assess the effectiveness of insecticides for management of M. morrisella
• Objective 1: Evaluate the toxicity of insecticides against adults of M. morrisella in the laboratory
Bioassays were completed to evaluate the toxicity of Agri-Mek and Endigo against adults through oral, contact and oral+contact exposure routes. Data from this experiment are currently be summarized and analyzed.
• Objective 2: Evaluate the efficacy of insecticides against M. morrisella in soybean fields
A site to perform this experiment was identified near Henderson, MN. The insecticide application will occur in early to mid August.

Goal 2: Assess host preference and varietal resistance of soybean to M. morrisella
• Objective 1: Determine host preference and varietal resistance of two native plants and several soybean varieties for M. morrisella
Methodology was developed to evaluate the host range of this insect and seed were obtained for the experiment. Initial replications of the laboratory experiment comparing soybean, edamame and several other legumes were initiated in July and further replications will be conducted in August. Similar methods will be used for a comparison among soybean varieties and will be conducted in September and October.
• Objective 2: Characterize relationship between abundance of M. morrisella in soybean fields and in native plants in wooded areas in close proximity
Multiple locations around the state were identified for this sampling. Sampling was initiated during this reporting period and will likely continue into September.

Update:

View uploaded report

Update:
Reporting period: 1 November 2023 to 30 January 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: Assess the effectiveness of insecticides for management of STL
• Objective 1: Evaluate the toxicity of insecticides against adults of STL in the laboratory
• Objective 2: Evaluate the efficacy of insecticides against STL in soybean fields
Goal 2: Assess host preference and varietal resistance of soybean to STL
• Objective 1: Determine host preference and varietal resistance of two native plants and several soybean varieties for STL
• Objective 2: Characterize relationship between abundance of STL in soybean fields and in native plants in wooded areas in close proximity

Specific project achievements during this reporting period:

Goal 1:
As previously reported, two experiments were performed to evaluate the toxicity of insecticides against STL. A laboratory bioassay showed that Agri-Mek and Endigo were toxic to STL adults through oral, contact and oral+contact exposure routes, with oral exposure being more toxic than contact exposure. In addition, a field insecticide efficacy experiment showed that Endigo provided better protection of the soybean canopy from STL than did Agri-Mek.

Goal 2:
The host preferences of STL were assessed in laboratory experiments. To assess the host range of STL, mated adults were allowed to oviposit for a defined period on different species of legume crop species (including soybean) in choice and no-choice settings. Across these experiments, STL show very strong preferences for soybean, with very few eggs being laid on any other legume crop species. Furthermore, the few eggs laid on legume crop species other than soybean did not develop to adults.
The potential for soybean varietal resistance to STL was assessed in laboratory choice and no-choice experiments. Mated adults were allowed to oviposit for a defined period on different genotypes of soybean including genotypes known to be resistant or susceptible to other pests, such as defoliators or aphids. This experiment is underway and will be reported on in the next progress report, but preliminary results suggest that some soybean genotypes with known resistance to other insects may also have resistance to STL.
To characterize the relationship between the abundance of STL in soybean fields and in native plants in wooded areas, multiple locations around the state were identified and sampled. Sampling was performed and results still need to be summarized and analyzed.

Challenges encountered
No problems occurred during this period

Dissemination of data/information during this reporting period

Scientific presentations:
Fuhr, F.M., A.V. Ribeiro, J.P. Menger and R.L. Koch. 2023, November. Lethal effects of insecticides against adults of Macrosaccus morrisella through multiple exposure routes. Meeting of the Entomological Society of America. National Harbor, MD.

Extension presentations:
Koch, RL. 2024, February. Biology and management of two new insect pests of soybean, soybean gall midge and soybean tentiform leafminer. Research Updates for Agricultural Professionals, Institute for Agricultural Professionals, University of Minnesota Extension. (30-minute presentation online with 55 attendees)
Ribeiro, A.V. and R.L. Koch. 2023, December. Evaluating control methods for a new leaf-mining pest of soybean in Minnesota. Prairie Grains Conference. Grand Forks, ND. (15-minute presentation with 30 attendees)

Macrosaccus morrisella is a new pest that might pose a significant threat to soybean production. Currently, knowledge about this pest in soybean is limited and the potential economic impacts to soybean production is unknown. 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 their risk for this pest. More specifically, recommendations for chemical and cultural control (i.e., varietal resistance) will be generated to help the farmers with actionable management tactics to protect their crops.

Indirectly, the proposed work rearing this insect in the laboratory should advance our abilities to maintain year-round colonies of this insect. Having the ability to produce M. morrisella in the laboratory year-round would advance all aspects of M. morrisella research and greatly increase the rate at which management recommendations are being developed to help farmers protect their crop from this pest.