Keep an eye out for these three ‘new’ insect pests

Entomologists are tracking the progress of cereal leaf beetles,cabbage seedpod weevils and pea leaf weevils across Manitoba

A provincial entomologist is asking farmers and agronomists to keep their eye out for three pests making inroads in Manitoba.

Why it matters: Provincial entomologist John Gavloski has a watch list of pests starting to creep their way into Manitoba.

The cereal leaf beetle was first spotted in Manitoba in 2009 and has spread from west to east. It’s the most widespread of the three, but seems to be contained below economic levels, said John Gavloski, entomologist with Manitoba Agriculture and Resource Development.

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It might, however, be creeping toward problematic levels, he added.

Gavloski presented on the pests during this year’s online Ag in Motion event, held July 21-25.

Adult cereal leaf beetles will feed between the veins on cereal plants, making long incisions. However, the larvae cause the most damage, Gavloski said.

Larvae make themselves less attractive to predators by covering themselves with their own feces — called a “fecal shield,” he added. They then strip the upper tissue off the leaves of cereals, forage grasses and some grassy weeds like wild oats.

“It looks like long, white streaks on the leaves,” he said.

The best time to scout for these pests is when the cereal is about to go into the boot stage. Before the boot stage, the threshold is three larvae per plant. Once the flag leave emerges, the threshold drops to one larva per flag leaf, according to the province.

Manitoba Agriculture and Resource Development is doing sweep net sampling for cereal leaf beetles, with a focus on the eastern part of the province. It’s collecting larvae to send to a lab for dissection to check for parasites.

Since cereal leaf beetles were first found in Manitoba, the province has had a biological control program which releases a parasitic wasp species in areas where the beetle is found.

“They only attack the cereal leaf beetles,” Gavloski said, adding that the program has been very effective.

The cabbage seedpod weevil, which is native to Europe, was first found in North America in 1936. It came to Saskatchewan in 2000 and made a “big jump” into Manitoba in 2017, Gavloski said.

After an extensive survey that year, the province determined the weevil wasn’t an economic threat.

“It still isn’t,” Gavloski said.

So far the weevils have been found in the western part of the province.

The cabbage seedpod weevil lays its eggs in certain species of brassicas like canola and some mustard species. The larvae then eat the seeds.

Once larvae are there, a producer can’t really do anything, said Gavloski. He suggested taking a sweep net to field edges and doing two sets of 10 sweeps on one side of the field, and two sets of 10 sweeps on the opposite side.

If producers find anything more than 25 to 40 weevils in 10 sweeps, on average, then the insects have reached economic levels. In Manitoba, he’s typically seen one or two weevils in 10 sweeps.

Pea leaf weevils were sparse in Manitoba last year but, “we know we have them,” Gavloski said.

Pea leaf weevil larvae eat nodules on the roots of peas and fava beans, potentially risking nitrogen deficiency in the plants if too many nodules are eaten.

Adults will eat the plant’s leaves, but this causes less damage, according to the entomologist.

As the adults are above ground, they’re likely easier to spot, but Gavloski said the adults are good at dropping to the soil and playing dead when someone approaches.

He suggested counting notches in the plant’s clam leaves. If on average more than 30 per cent of seedlings have notches on clam leaves, the weevils may be reaching economic damage levels.

Gavloski asked anyone who found pea leaf weevils to report them.

About the author

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Geralyn Wichers

Geralyn Wichers grew up on a hobby farm near Anola, Manitoba, where her family raised cattle, pigs and chickens. Geralyn graduated from Red River College’s Creative Communications program in 2019 and was previously a reporter for The Carillon in Steinbach. Geralyn is also a published author of science fiction and fantasy novels.

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