Wheat School: Updating the wireworm species survey, 80 years later

(W. Van Herk/Supplied)

Believe it or not, there hasn’t been an updated survey on wireworm species across Alberta, Saskatchewan, and Manitoba since 1943.

That all changes now that a research team has taken on the task.

Ted Labun, seedcare technical lead for Western Canada at Syngenta Canada, explains in this Wheat School episode why the survey needed to be updated, and what he has learned alongside the research team that co-authored the publication.

Labun’s interest in wireworms started in 2005 , when Syngenta introduced a seed treatment for protection against the pest. “Over those first four to five years, I was learning a lot about wireworms and I didn’t understand a lot about them,” says Labun.

Wireworms have been around for decades, but different species and growing conditions can impact wireworms’ effect on crops differently.

Labun was able to work with experts in the wireworm field, including Drs. Robert Vernon and Willem van Herk, numerous extension professionals, and staff at retail locations. Those working relationships resulted in a co-authored paper titled “Distribution of Pest Wireworm Species in Alberta, Saskatchewan, and Manitoba.”

During the survey, from 2004 to 2019, samples were collected from 571 farmland locations where crop damage from wireworms was suspected or observed, and a total of 5,704 specimens were identified. Most were of four main species: Hypnoidus bicolor, Selatosomus aeripennis destructor, Limonius californicus, and Aeolus mellillus.

“There’s been a big change from 1943 moving forward to 2021. Certainly the crops have changed, rotations have changed, we do direct seeding now, we also do continuous cropping,” says Labun. “I thought that the more we understand about the wireworms, the distribution, the different species, and how that might impact management would be important.”

When Labun started with the project, ‘destructor’ was the main species on the Prairies, but ‘bicolor’ has dominated the growing region since. Labun and the research team think that the shift in dominant species is due to agronomic practices, soil characteristics, rainfall, and related soil conditions.

The life cycles of these two species are very different from one another — adult ‘bicolor’ click beetles will lay eggs and in two or three years, that generation will become adults, whereas ‘destructor’ can remain in the wireworm stage for nine years.

“It’s a very different dynamic when you look at the species and how they might impact the crop,” says Labun. In Labun’s personal experience, cereals seem to be the number one crop that click beetles like to lay their eggs in, but has also found that lentils, corn, and potatoes are susceptible to wireworm damage.

Preferred soil temperature varies between species, but Labun says that when the temperature starts to reach five degrees Celsius, wireworms become active and when it starts to get very hot and dry, wireworms will migrate downwards into the soil, which affects damage levels to the crop.

“In the Black soil zone, they seem to be more the Hopnoidus bicolor. In the southern Prairies, we’ve seen more ‘destructor,’ the grey-green wireworm, and also if we take a look at the Limonius californicus, it’s usually that we find it in irrigation, but we’re also finding it more now in dryland conditions where there’s more consistent moisture, and I think that has to do with reduced tillage,” says Labun.

Scouting is Labun’s number one recommendation when dealing with wireworms early in the season, adding that depending on the time of spring, damage may or not be so obvious.

Catching wireworms can be done with an oatmeal baitball, or by a vermiculite/wheat trap in a plastic pot with a lid. Labun explains that wireworms are attracted to carbon dioxide in the soil, and as soon as the wheat seed germinates, it sends a signal to the wireworm.

“The one thing about wireworms, is you can’t see them,” says Labun. “When you go into a field, the one technique I use is I look for skips in the field, or areas where it’s very thin sand. Another way I can always tell if there’s wireworms is that they take out the crop really early in the season, and then you have no crop competition [for weeds].”

Labun says that click beetles are much easier to identify than wireworms, and can be caught with a pitfall trap. There’s also a great wireworm guide published by Agriculture and Agri-Food Canada that’s available, to help producers differentiate the species in the field.

“The species do make a difference, and the big thing I learned is that, depending on the species, one wireworm can do less or more damage,” says Labun. At the end of the day, the two main species will do different amounts of damage to a crop, but seed treatment is still the major line of defence against wireworms.

Labun adds that seeding depth, depending on the depth of moisture, is also a factor. “Seeding deep is not great, because the longer it takes for that seedling to come out of the ground, the more vulnerable it’ll be to feeding.”