Could these microscopic beneficials be effective biocontrol tools for Prairie crops?
March 22, 2023 By Caroline King
Entomopathogenic nematodes (EPNs) – also known as predatory or insecticidal nematodes – are tiny, soil-dwelling roundworms that attack insects. Certain EPN species have been shown to provide safe, effective management of some serious crop insect pests in other parts of North America. Shabeg Briar is conducting research at Olds College of Agriculture and Technology to see if these EPNs can be effective biocontrol agents in Prairie crops.
“Our long-term goal is to add another tool to the toolbox for controlling insect pests, especially root maggots and cutworms,” says Briar, who is a research agronomist with the Olds College Centre for Innovation in Olds, Alta.
His current project builds on an initial phase of his EPN research, which was completed in 2020. In that one-year laboratory study, Briar and his colleague, Paul Tiege, assessed the effects of EPNs on four canola pests, including flea beetle, diamondback moth, lygus bug and cabbage root maggot, as well as on black cutworm, which is a pest of many broadleaf and grass crops.
That study tested various concentrations of four commercially available EPN species: Steinernema kraussei, Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora. For the study’s foliar insects – flea beetle adults, diamondback moth larvae and pupae, and lygus bug nymphs – the EPNs were applied to the insects in Petri dishes. For the below-ground pests – cabbage root maggot larvae and pupae, and black cutworm larvae – the EPNs were applied to the insects in small cups with sandy soil.
The effectiveness of the EPNs depended on the nematode’s species and concentration, and on the pest insect’s species and life stage. Overall, the EPNs caused significant mortality in the larval stages of diamondback moths, cabbage root maggots, black cutworms and lygus bug nymphs. The mortality levels were very low in the flea beetle adults.
Briar’s current project runs from spring 2022 to spring 2024. This project is assessing the effects of EPNs on cabbage root maggots and black cutworms. He is targeting these particular pests in part because samples of these insects are easily accessible. “Black cutworm larvae are commercially available from the U.S., and we can collect root maggots from Alberta fields infested with this pest.”
This project has two main components. So far, Briar’s team has completed the first component, a controlled environment experiment to examine the effects of the commercially available EPNs on root maggots and black cutworms. They applied the four EPNs using a soil drench method and compared different application rates.
Briar outlines the key findings: “For black cutworms, Steinernema feltiae, S. kraussei, and S. carpocapsae caused significant mortality. For root maggots, both S. feltiae and S. kraussei were effective in causing mortality, thereby significantly reducing root damage to canola plants in the growth chamber.”
At present, the team is working on the project’s second component, an investigation of the possibility of using local EPN strains for controlling the two pests.
For this work, they first have to conduct surveys to find local EPNs. “In 2022, we collected soil samples from different fields in Alberta, especially in central Alberta. We also received some soil samples from Fort Vermilion (MARA [Mackenzie Applied Research Association]), Forestburg (BRRG [Battle River Research Group]) and Lacombe (FCDC/AAFC [Olds College Field Crop Development Centre, and Agriculture and Agri-Food Canada] research fields),” notes Briar. He adds, “We have the GPS location for each sample so we can go back to the sampling site if we need to.”
Next, they test each soil sample to see if any EPNs are present. To do that, they put the sample in a small cup and add EPN bait into the cup. For the bait, they use waxworms, commercially available larvae of the moth Galleria mellonella. If any EPNs are present in the soil sample, the nematodes will kill the waxworms and start multiplying in the waxworm bodies.
“There are a few ways by which we can know if the waxworms are infected or not,” explains Briar. “For example, infected larvae will show some colour change within about three or four days. We collect any infected larvae and put them on filter paper in a Petri dish. Then we run the bioassay for another few days. If any predatory nematodes are present, they will multiply and then leave the insect in high numbers. That shows us that the sample is positive.
“If the sample is positive, then we re-culture the nematodes two or three times to confirm that EPNs are definitely present.”
In 2022-23, the team tested 77 soil samples and found 14 positive samples. With further testing, they focused on two or three of the most promising samples.
They are now working on the challenging step of identifying the EPN species in these promising samples. Briar says, “We had preliminary molecular analysis done with the help of a University of Calgary post-doctoral researcher. She determined that the genus is most likely Steinernema. It might be a new species in this genus, but we have a lot of work to do before we could confirm that.”
In the coming months, the team will continue working on the species identification and run bioassays to compare these local EPNs with the commercially available EPNs to see how effective they are at killing root maggots and black cutworms.
The team also plans to collect more soil samples in 2023 to see if they can find more local EPNs for identification and testing.
According to Briar, the Alberta Canola Producers Commission has shown a lot of interest in the possibility of using EPN applications for managing the cabbage root maggot. He notes that this pest can cause yield losses especially in short canola rotations, and no chemical insecticide products are currently available for controlling it.
So, after this current project is completed in 2024, Briar would like to move on to the next phase of this EPN research, which could include Alberta field trials.
He emphasizes it will take time to fully evaluate if EPNs could be a sustainable, cost-effective, practical option for controlling pests like root maggots and black cutworms under Prairie growing conditions. He is also interested in seeing whether the local EPNs might be better adapted and more effective under Prairie conditions than the commercial strains.
Briar sees a good potential for using EPNs as part of an integrated pest management strategy for root maggots, black cutworms and possibly other Prairie crop insect pests. He notes that EPNs are already being used commercially in the U.S. as a tool in the management of various insects, mainly in the turfgrass and horticulture industries, but also some field crop pests like corn rootworms and alfalfa snout beetles.
Briar’s current project has received funding from Results Driven Agriculture Research, the Canadian Agricultural Partnership and the Alberta Canola Producers Commission, as well as Mitacs funds for a student intern.