Scale-up and release of Diadromus pulchellus, a biological control agent of leek moth, and knowledge transfer of an Integrated Pest Management toolbox to growers

Project Code PRR-STB19-020

Project Lead

Kathryn Makela and Jacob Miall, Agriculture and Agri-Food Canada

Objective

To improve control of leek moth in Ontario and Quebec allium growing regions by increasing populations of the biological control agent, Diadromus pulchellus and disseminating Integrated Pest Management (IPM) information to growers

Background

The leek moth, Acrolepiopsis assectella, is an invasive pest from Europe that causes damage to alliums crops, including onions, leeks and garlic. Allium production is an important sector in Canada with dry onion farm gate value reaching $95M in 2018. Leek moth larva burrow into the leaf, weakening and withering the plant, resulting in crop losses. Since first detected in Eastern Ontario in 1993, leek moth has rapidly expanded its range in southwestern Ontario, Quebec, Prince Edward Island, Nova Scotia and the US. Moreover, current scientific models predict further expansion of leek moth range across Canada and North America, mainly as a result of climate change. It has also been documented that more generations of the pest within a growing season result in greater damage to plants, rendering later season crops unmarketable. In Ontario, the leek moth completes three generations in a growing season, but increasing temperatures may provide adequate degree-day accumulations for additional generations.

Through previous work carried out by Agriculture and Agri-Food Canada researchers over the past two decades (Leek moth a pest of Allium spp.: pest biology studies and the development of a reduced risk IPM strategy for control; Biological control of the leek moth, a pest of Allium spp; and Release of a parasitic wasp for biological control of leek moth) several tools contributing to an IPM approach for leek moth were developed. These included the discovery of, and initial releases of a biocontrol agent, the parasitic wasp Diadromus pulchellus (Hymenoptera: Ichneumonidae), identified at CABI Bioscience in Delémont, Switzerland and introduced in Canada in 2010 following several years of laboratory efficacy testing. Additional research led to the development of a degree day model for leek moth, monitoring techniques, as well as exploring alternative control solutions and practices.

This project aimed to build upon and advance previous scientific outcomes by putting into operation a multi-pronged, integrated approach package readily accessible for grower adoption to help with slowing down the spread and sustainable management of leek moth in allium crops.

Approach

Scaled-up rearing and releases of the parasitic wasp D. pulchellus. Colonies of D. pulchellus were mass reared at the AAFC’s Ottawa Research and Development Centre lab along with leek moths to provide host material for the biocontrol. Selection of field sites and releases of D. pulchellus were coordinated in collaboration with provincial specialists from the Ontario Ministry of Agriculture, Food and Rural Affairs and Quebec Ministry of Agriculture, Fisheries and Food. Provincial collaborators identified grower cooperators as well as suitable garlic, onion and leek farms in their respective regions with significant leek moth population levels to conduct releases.

Monitoring for D. pulchellus establishment following 2019-2021 releases. In each project year, efforts were made to determine overwintering success and establishment of D. pulchellus populations across the release sites. Prior to new seasonal releases, wild and/or sentinel leek moth pupae were collected from the fields where releases occurred the previous year and reared to determine parasitism levels and species composition. Recoveries of D. pulchellus from this first generation confirmed adult overwintering success from the previous fall.

Leek moth development and degree-day monitoring. An interactive dashboard was developed on the MS Excel platform to integrate a degree-day developmental model with flight trap captures for use as a tool to determine ‘action windows’ for different management strategies. This tool was tested and validated in the 2020 and 2021 field seasons.

Results

Releases of D. pulchellus started in summer 2019, with 1 to 3 deliveries per selected site staggered throughout the season. Releases were timed in advance of the 2nd and 3rd generations of leek moth pupae at six farm sites in Ontario (Perth, Centreville, New Hamburg and Ottawa areas) and two farm sites in Quebec (in Saint-Camille and Hatley areas). A total of 4,250 and 2,320 D. pulchellus adult females and males were released in Ontario and Quebec, respectively in 2019. Due to public health restrictions in place, only small scale releases (150 adults) could be delivered in two Quebec sites in September 2020. Similarly in 2021, small releases were only delivered in one site in Quebec (800 adults) and one site in Ontario (400 adults) between July and September. The same sites were consistently used for releases.

Progeny of D. pulchellus individuals released in 2018 (prior to the start of this project) were recovered in 2019 indicating that the parasitic wasp successfully overwintered in eastern Ontario and Quebec. Progeny of individuals released in 2019 were also recovered in 2020, once again demonstrating that D. pulchellus had successfully overwintered.

Field testing of the interactive dashboard degree day forecasting model demonstrated results similar to previous models in its ability to predict the developmental stages of leek moth. This model, coupled with field observations can help to provide meaningful management action recommendations. Some additional modification and adjustments may occur over the following field seasons to validate the efficacy of the model, prior to its distribution to select growers to utilize the tool for their own decision making needs.

Conclusions

This project has furthered the effort to expand the established range of D. pulchellus in areas of eastern Canada where leek moth is present. Findings from lab and field overwintering studies undertaken by this project will help establish new methods for rearing and stockpiling of the parasitoid to improve efficiencies of large-scale releases. Post-release monitoring from year to year at the release sites has confirmed parasitoid establishment, which may lead to reducing the need for new releases moving forward. The hope is that releases will result in stable establishment and eventual spread of the agent across the leek moth range. Presence of an effective biological control agent in allium-producing regions before leek moth populations reach economically damaging levels could mitigate their capacity to harm the industry.

A simpler and more intuitive leek moth monitoring dashboard developed as part of this project will enable expanded tracking of leek moth populations. Also, the long-term plan is to package the leek moth forecasting tool into user-friendly format for wider grower access to support making informed management decisions. Finally, availability of an IPM program that effectively combines the above tools and other practices, is expected to support sustainable leek moth management and help reduce risks to the environment by providing an alternative to chemical pesticides and calendar based spray programs.

The lockdown due to pandemic heavily impacted the outreach plans and the knowledge transfer portion of this project. Outreach activities, such as presentations at grower meetings, articles in grower media, online webinars, are necessary to increase awareness within the sector and promote adoption of beneficial practices identified in this research.