To determine the effects of wheat-canola rotation on wireworm and carabid populations. To identify the most effective trap method for monitoring populations of these pests and beneficial insects. To assess the feasibility of using molecular DNA techniques to determine the importance of carabids as predators of wireworm. To provide producers with an up-to-date field guide on wireworm identification and control.
Wireworms, the underground larval stage of various species of click beetles, are a serious pest of many crops across Canada. These long-living soil-dwelling larvae eat cereal and pulse seeds and seedlings, causing crop thinning. Wireworms are hard to detect and move up and down in the soil profile. At the time of this research, there were no chemical options registered that would lower wireworm populations in a field, making the pest a major frustration for many farmers. Our main objectives in this study were to learn about wireworms in southern Alberta wheat fields and determine if crop rotations are related to wireworm populations. We also wanted to study beneficial ground beetle populations in the same fields, these beetles can be predators of crop pests and weed seeds. Finally, we wanted to produce a field guide for Prairie wireworms to help farmers and industry learn about these mysterious pests.
We sampled 12 commercial spring wheat fields within a 90-minute drive from Lethbridge each year in summers 2017-2019 with various rotations in the previous 2 years. We selected new fields each year. In 2017-2018 our wheat fields were preceded by cereal-cereal, cereal-canola, or canola-cereal, and in 2019 we added wheat fields with a pulse-canola rotation. We used underground bait traps and soil cores for wireworm, and ground-level pitfall traps for click beetles (adult wireworms) and ground beetles (beneficials).
Over the course of the study, we deployed 273 bait traps and collected 5,826 soil cores for larval wireworms. We caught 1,336 wireworms, which were all native Prairie species: Hypnoidus bicolor (59%), Selatosomus aeripennis destructor (24%), Aeolus mellillus (9%), Limonius californicus (5%) and Hadromorphus glaucus (2%). We deployed 2,834 ground-level traps, and caught 26,424 click beetles, 99.9% of which were of the same 5 species as above. All fields had H. bicolor and at least 1 other wireworm species, but in different amounts and proportions. One field had 5 species of wireworms! There was huge variation in wireworm abundance and species composition between fields, even sometimes when fields were just hundreds of metres apart. However, any possible signals in the data from crop rotation were non-existent or inconsistent. There are many benefits to having a diverse crop rotation, but unfortunately, wireworm management does not seem to be one of them.
Our 2,834 ground-level traps also caught 98,720 ground beetles from 82 species in 29 genera. Two species were new records for Alberta. Like the click beetles, ground beetle abundance and diversity varied by field. But, more than 9 out of 10 ground beetles caught belonged to just 3 species: seed-eaters Amara littoralis (48%) and Amara farcta (10%), and the predator Pterostichus melanarius (34%). P. melanarius was 10x more abundant in irrigated fields than dryland. Ground beetle communities varied significantly with previous crop rotation: dryland wheat fields following canola in the previous year had more carabids of all genera and more beetles in the Amara (seed-feeding) genus, compared to fields following cereals. Therefore wheat fields following canola may have better weed seed predation.
We produced and published a wireworm field guide in 2021, titled “Guide to Pest Wireworms in Canadian Prairie Field Crop Production”. The guide, available in both English and French, is written in plain language and contains background information on wireworms, their research history on the Prairies, species descriptions and photos, management options, and research needs. Over 1,800 hard copies have been distributed at no cost to recipients which include farmers, agronomists, industry, researchers, students, instructors, funders and AAFC management. The guide is also available as a free pdf on the Government of Canada website www.publications.gc.ca.
This project generated new information about wireworms and ground beetles in southern Alberta and and helped spread the findings of new and old wireworm research. This project helped launch the new cereal crop entomology research program at AAFC-Lethbridge led by Dr. Haley Catton. It has led to collaborations in wireworm research across Canada, as well as follow-up projects in improving wireworm monitoring and management for the benefit of farmers.