Performing Department
(N/A)
Non Technical Summary
Our proposal centers on a devastating invasive plant pest, the Asiatic garden beetle (Maladera formosae, AGB), which threatens mint production in the north central region of North America. AGB is a scarab beetle that attacks more than 100 different plant species, including ornamentals, weedy species, and crop plants. The larval (grub) stage, feeds underground on plant roots for nearly 10 months of the year, causing severe injury and plant death. Given its relatively new status as a pest in perennial mint production, progress towards management has been slow. Insecticide options are limited to foliar insecticides for adults, which are not the damaging life stage in this system, and only one soil insecticide is labelled for the damaging larval stage. Meanwhile, growers are under increasing pressure from buyers to produce mint more sustainably.Limited knowledge of the success and sustainability of biological control strategies for AGB larvae in mint, and the potential influence of environmental factors on the outcome of these strategies pose key decision-making challenges for mint producers, who continue to suffer significant losses. We propose to evaluate the persistence and efficacy of entomopathogenic nematodes (EPNs) over a two-year period at field scale, in collaboration with affected growers, to explore their potential as a biological management option for AGB. We will identify key soil and EPN-related factors that influence the persistence and efficacy of EPNs so we can develop and support the implementation of a sustainable management solution for growers. Specifically, we will 1) evaluate the efficacy and longevity of persistent EPN strains against AGB larvae in commercial mint fields following inoculative release, 2) evaluate the role of key soil characteristics in determining the persistence and infectivity of EPNs against AGB larvae, and 3) implement and evaluate a self-sustaining extension program for AGB management in Indiana mint. Upon completion, we expect this project to improve the sustainability and cost-effectiveness of IPM strategies for AGB in commercial mint production in the north central region.
Animal Health Component
80%
Research Effort Categories
Basic
0%
Applied
80%
Developmental
20%
Goals / Objectives
The major goals of this project are to provide mint growers with the knowledge needed to determine: A) if entomopathogenic nematodes (EPNs) are an effective approach for keeping Asiatic garden beetle (AGB) larval densities below damaging levels, B) how long protection by EPNs may last against AGB larvae, and C) whether factors like soil texture, or bulk density, may also impact the success and persistence of EPNs against AGB in mint. Our specific research objectives are:1. Evaluate the efficacy and longevity of persistent strains of entomopathogenic nematodes against AGB larvae in commercial mint fields.2. Evaluate the role of key soil characteristics (texture, organic matter, bulk density, and water holding capacity) in determining the persistence and infectivity of entomopathogenic nematodes against AGB larvae in mint.3. Implement and evaluate a self-sustaining extension program for AGB management in Indiana mint.
Project Methods
Objective 1: Evaluating the efficacy and longevity of persistent strains of EPNs against AGB larvae in commercial mint fieldsWe will evaluate the long-term survival and ability of persistent H. bacteriophora and S. feltiae entomopathogenic nematodes (EPNs) to maintain populations of damaging scarab larvae below our established damage threshold of 55.6 grubs/m2 in commercial mint fields.To characterize scarab larval densities and mint yield, we will use a field-based, yield harvest and soil-excavation approach we have developed previously, whereas EPN persistence will be monitored using a well-known and effective soil baiting technique commonly used to assess EPN populations. Scarab larvae and mint samples will be collected in a grid pattern from each block. The sampling grid in each block will consist of a series of 32, 31.8 m2 cells (5.6 × 5.6 m) (plots).One, 0.25 m2 quadrat fashioned from ¾" PVC pipe will be placed in the center of 15, randomly selected plots within each grid, and all living mint stems and leaves will be cut at the soil surface. Above-ground plant material will be collected and weighed as a measure of yield. Within the same 0.25 m2 quadrats, all soil will be excavated to a depth of 10 cm. Each 0.006 m3 mass of soil will be broken apart and sieved through a 0.32 cm hardware cloth mesh to collect the grubs. The number, species, and instar of all white grubs will be recorded and the number of white grubs within each sample will be used to estimate mean grub density within each 32-cell block. Scarab larval populations and mint yields in each of the 6 blocks will be assessed during the fall (September-October) of each year.EPN populations will be characterized by baiting the soil with G. mellonella larvae three times during each growing season (May, July, September) for the duration of the project. We will examine the same 15 randomly selected plots used to quantify scarab larval densities and mint yield. Three 1.9 cm soil cores will be taken at random from within each plot, placed into labelled plastic bags and immediately placed in a cooler. The next day, soil samples will be broken apart by hand and 10 waxworm larvae (Galleria mellonella) will be placed inside each bag in contact with the soil. Bags will be sealed and held in the dark at room temperature for 3 days. At that time, dead waxworm larvae will be removed from the bags and placed on White's traps to confirm nematode infection as the cause of death. Dead waxworms will immediately be replaced by adding fresh waxworms to the bags. This process will be repeated a total of two times for each soil sample or until no further infection is indicated. All waxworm cadavers with signs of nematode infection will be transferred to White's traps and infective juveniles will be allowed to emerge.Data analysis. We will use ANCOVA (AGB larval populations 1x/year) and repeated measures analysis (EPN infectivity 3x/year) to make comparisons between treated and untreated blocks using soil characteristics as covariates. These comparisons will be performed using the mean values for each block estimated from the 15 plots sampled within each block. Bootstrapping will be performed as necessary using multiple random subsets of 10 of the 15 individual plots in each treated and untreated block to provide additional estimates of the means and confidence intervals for comparison. We will examine how variation in soil characteristics such as texture, organic matter, bulk density, % moisture, and water holding capacity correlate with AGB population densities and EPN infectivity using multiple regression analysis.Objective 2: Evaluating the role of key soil characteristics in determining the persistence and infectivity of EPNs against AGB larvae in mintWe will evaluate AGB larval suppression by commercial and persistent EPN strains in soil types that are common across commercial mint fields in Indiana. This experiment will use a factorial design that includes the following treatments: 1) untreated soils, 2) commercial EPNs, and 3) persistent EPNs. We will include 3 different soils; sand, loamy sand, and silty-clay loam. Each treatment will include at least 5 experimental replicates in a 3 × 3 factorial design and we will conduct this experiment twice during the project timeline, once with H. bacteriophora and once with S. feltiae, each applied at a rate of 50 million/acre to mimic what was applied in cooperator fields during 2023. These studies will be conducted in potted mint plants in the greenhouse over a 14-day period so we can isolate the independent and combined effects of soil characteristics and EPN strain (commercial vs. persistent) on AGB larval mortality.A study to assess EPN persistence will be conducted in the absence of insect hosts. Using the three different soils described in the section above and both commercial and persistent strains of H. bacteriophora and S. feltiae. We will place 100 g of each soil into plastic snap-cap containers and deliver 1000 infective juvenile EPNs of uniform age into each container. Containers will be placed in an environmental chamber and held at 21°C (±1°) with weekly moisture adjustments made as necessary to maintain adequate soil moisture for the two different species. Initially, and then at 4-week intervals thereafter, 5 containers of each soil × EPN combination (3 × 3 factorial) will be removed from the chamber and the soil for each will be adjusted up to 15% moisture. The moistened soil will be placed into plastic Ziploc bags and 10 waxworms will be added to each. Bags will be held in the dark at room temperature for 3 days. Dead waxworm larvae will then be removed from the bags and placed on White's traps to confirm nematode infection as the cause of death.Data analysis. Variation in the number of living AGB larvae found in each treatment will be examined using factorial analysis of variance with soil texture and nematode treatment as the independent variables. Treatment means will be compared to untreated controls using Fisher's least significant difference (LSD) test. The influence of soil texture and EPN treatment on EPN persistence will be assessed using a factorial repeated-measures model with the number of infected waxworms serving as the response variable.Objective 3: Implement and evaluate a self-sustaining extension program for AGB management in Indiana mintWe will build upon our current extension program for AGB best management practices in commercial mint by translating results from the 2-year study we propose here into recommendations. We will deliver information in three forms: 1) extension bulletins, which will include information on the life cycle and biology of AGB and EPNs, how to apply EPNs, and their management potential for AGB in mint, 2) extension videos, which will include step-by-step demonstrations of entomopathogenic nematode application and the appearance of AGB grubs that are infected with EPNs, and 3) on-site programming at the annual Midwest Mint Grower Meetings in Fair Oaks, Indiana.Efforts & Evaluation. Programming at the annual Midwest Mint Growers Meeting will provide a venue for face-to-face delivery of recommendations coming from this research, as well as an opportunity to directly assess its impact. To evaluate the latter, we will deliver research updates and a pre-survey (digitally and on paper) at the 2025 Midwest Mint Growers meeting to measure stakeholders' initial knowledge of the biology and life cycle of EPNs and their likelihood of adopting them as a biological control strategy. We will survey stakeholders again at the 2026 Midwest Mint Growers Meeting to measure changes in their knowledge of and likelihood of adopting EPNs. We will also track the number of views and downloads across our extension and research webpages to measure the impact of our new extension bulletins during and after the project timeline.