Updated May 31, 2024:
Reporting period: May 1, 2023 to April 30, 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:
Studies with the insecticides Agri-Mek SC (abamectin) and Endigo ZXC (lambda-cyhalothrin + thiamethoxam) were developed with the objective to evaluate the effects against adults of M. morrisella through different routes of exposure; and the efficacy of field applications. In the experiment with adults, the survival of M. morrisella exposed to insecticides through oral exposure, or residual contact + oral exposure, was significantly lower than that for residual contact exposure alone, which in turn was lower than the untreated control. Within each exposure route, the response to the two insecticides did not differ. In the field experiment, at 21 days after insecticide application, the mean percentage of leaf area mined was significantly lower in plots treated with Endigo ZCX compared to plots treated with Agri-Mek SC or those left untreated. Taken together, these results suggest that Endigo ZXC and to a lesser extent Agri-Mek SC may have potential for management of M. morrisella.
Goal 2:
The threat posed by STL to other legume crops and the potential for host-plant resistance for management of this pest in soybean are currently unknown. Thus, complementary choice and no-choice experiments were carried out to assess the host range of STL among different species of legume crops and among different genotypes of soybean. STL was found to oviposit on its native host American hogpeanut and soybean (both grain and vegetable types), but not on red kidney bean, white kidney bean, cowpea, chickpea, fava bean, pea, and lentil. Low levels of oviposition were observed on mung bean and lima bean in a choice test, but no larvae of STL survived on either of those legumes. When soybean genotypes were compared, lower oviposition of STL was observed on the PI229358 and PI227687 in choice and no-choice oviposition tests, and lower survival rates of STL were observed on the PI229358 and M15-105140 in a no-choice test. Taken together, the results of this study indicate that the host range of STL appears to be restricted to the previously known native hosts and soybean, but continued monitoring for adaptation to other legumes is necessary. Furthermore, potential sources of soybean resistance against STL were identified and could be utilized in soybean breeding programs for development of host-plant resistance for management of this new soybean pest.
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:
Koch, R.L., A.V. Ribeiro, J. Menger and F. Fuhr. 2024, March. What do we know about the biology and management of the soybean tentiform leafminer, a new pest of soybean? Meeting of the North Central Branch of the Entomological Society of America. Fort Collins, CO.
Koch, R.L. 2024, February. Biology and management of the soybean tentiform leafminer. 25-minute talk. Soybean Breeder’s Workshop, St. Louis, MO.
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.
Scientific publications:
Führ, F.M., A.V. Ribeiro, J.P. Menger and R.L. Koch. Potential for chemical control of the soybean tentiform leafminer (Lepidoptera: Gracillariidae), a new pest of soybean. Journal of Economic Entomology (undereview with journal)
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)
Extension publications:
Ribeiro, A.V. and R.L. Koch. 2024. The soybean tentiform leafminer has been found in 51 counties in Minnesota, North Dakota and South Dakota. Minnesota Crop News, University of Minnesota Extension. January 9, 2024 https://blog-crop-news.extension.umn.edu/2024/01/the-soybean-tentiform-leafminer-has.html
Macrosaccus morrisella (soybean tentiform leafminer (STL)) is a tiny moth native to North America. It was found attacking soybean in the United States for the first time in 2021. The immature stage (larva) of this moth lives and feeds inside leaves, leading to loss of functional leaf area (i.e., defoliation). In 2022, STL 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. Such levels of defoliation by insect pests can significantly decrease soybean yield.
The appearance of a leaf-mining insect like STL 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. Furthermore, the leaf-mining moth M. robiniella, a related species of M. morrisella, is a significant pest of ornamental plants in Europe. Thus, research is urgently needed to assess the potential impacts of STL and how to manage its infestations. Unfortunately, there is only limited knowledge on STL in the forest systems where it historically occurred in Eastern North America and even less knowledge about it in soybean.
To build the foundation for the development of management programs for STL, we pursued the following goals: 1: Assess the effectiveness of insecticides for management of M. morrisella; and 2. Assess host preference and varietal resistance of soybean to M. morrisella.
Studies with the insecticides Agri-Mek SC (abamectin) and Endigo ZXC (lambda-cyhalothrin + thiamethoxam) were developed with the objective to evaluate the effects against adults of M. morrisella through different routes of exposure; and the efficacy of field applications. In the experiment with adults, the survival of M. morrisella exposed to insecticides through oral exposure, or residual contact + oral exposure, was significantly lower than that for residual contact exposure alone, which in turn was lower than the untreated control. Within each exposure route, the response to the two insecticides did not differ. In the field experiment, at 21 days after insecticide application, the mean percentage of leaf area mined was significantly lower in plots treated with Endigo ZCX compared to plots treated with Agri-Mek SC or those left untreated. Taken together, these results suggest that Endigo ZXC and to a lesser extent Agri-Mek SC may have potential for management of M. morrisella.
The threat posed by STL to other legume crops and the potential for host-plant resistance for management of this pest in soybean are currently unknown. Thus, complementary choice and no-choice experiments were carried out to assess the host range of STL among different species of legume crops and among different genotypes of soybean. STL was found to oviposit on its native host American hogpeanut and soybean (both grain and vegetable types), but not on red kidney bean, white kidney bean, cowpea, chickpea, fava bean, pea, and lentil. Low levels of oviposition were observed on mung bean and lima bean in a choice test, but no larvae of STL survived on either of those legumes. When soybean genotypes were compared, lower oviposition of STL was observed on the PI229358 and PI227687 in choice and no-choice oviposition tests, and lower survival rates of STL were observed on the PI229358 and M15-105140 in a no-choice test. Taken together, the results of this study indicate that the host range of STL appears to be restricted to the previously known native hosts and soybean, but continued monitoring for adaptation to other legumes is necessary. Furthermore, potential sources of soybean resistance against STL were identified and could be utilized in soybean breeding programs for development of host-plant resistance for management of this new soybean pest.
Overall, this research provides a foundation for development of integrated pest management (IPM) programs for this new pest. The efficacy of some insecticides is understood and provides an “emergency response” tactic, if farmers need to protect yields from this pests feeding injury. This work also establishes a foundation for development of host plant resistance for this pest (pest resistant soybean), which offers a more sustainable longer term control. Future work will evaluate additional insecticides and biological control, as well soybean yield response to STL feeding for creation of more robust IPM program.