Control challenges drive wireworm research

BANFF, Alta. — Entomologist Bob Vernon has counted wireworm larvae, identified species and looked for creative ways to kill them.

“It is a very difficult insect to work with and there are not many people in the world working on this right now,” he told the recent Potato Growers of Alberta annual meeting in Banff.

Vernon, who works at Agriculture Canada’s research centre in Agassiz, B.C., is involved in surveillance and insecticide field trials.

More than 20 economically important species have been identified in Canada since 2004. The worms are the larval stage of click beetles, but there is no single control because of the large number of species.

“Some species are not controlled by certain insecticides, so it is very important to know what you have,” Vernon said.

“If you are a potato grower and you are rotating with cereal crops, there is a problem if you have got a buildup of wireworm in that field and you plant the field into potatoes, the wireworms will cause damage to your potatoes. It doesn’t matter what crop you put into that field, they’ll eat it.”

Wireworms come in different shapes and sizes, and some can live for years in the soil chewing through crops.

Wireworm larvae are slender, jointed and hard-bodied. They have three pairs of legs behind the head, and the last abdominal segment is flattened with a keyhole-shaped notch. Fully grown larvae vary in length, depending on species, and range from one to four centimetres.

The species differ across Canada.

Samples have been received from 445 fields on the Prairies, and while hypnoides bicolor is the most dominant, selatosomus destructor and limonius californicus are moving into the Prairies.

“L. californicus seems to be a species that is gaining traction in southern Alberta,” Vernon said.

“I believe it will overtake some of the other species in certain areas.”

Californicus attacks cereals, but canola could be next.

A single field may have multiple species, all at different stages of their lives from eggs to adults.

Click beetles emerge in April and May when the soil is 10 C or warmer. The adults can walk or fly into fields to lay eggs, which become larvae three weeks later.

Lindane was the insecticide of choice before 2004, when it was banned. Researchers are searching for new chemicals that work as well. Insecticide efficacy trials started in 2013 at Agassiz using a product called Thimit as the industry standard for control and comparison.

Results have been mixed, but Vernon said there is hope.

The good news is that fipronil works better than lindane, and 90 percent of a population is eliminated. The bad news is that it is not registered in Canada, and populations of wireworms are increasing across Western Canada, threatening a variety of crops.

Montana researchers have been working with fipronil in potatoes using BASF’s Regent to see if it adds protection to subsequent rotations of wheat and pulses.

Research at Montana State University has shown that the product does reduce the wireworm population overall, similar to what Lindane once did. Work continues to create an insecticide for Canadian growers of cereals and horticulture crops such as potatoes. New products are also coming that can be applied at lower rates to reduce environmental impacts.

“If we can control them in wheat, for example, then we don’t need to worry about wireworms overwintering in your fields and damaging potatoes the next year,” Vernon said.

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