A canola pest called the cabbage seedpod weevil is developing pests of its own.
More than a dozen species of tiny, weevil larvae-eating wasps are shifting their tastes from other insect hosts to this voracious crop-eating weevil.
The Necremnus duplicatus strain represents a third of this family of cabbage seedpod weevils, with Trichomalus perfectus not far behind.
Just how much of the weevil population is being eaten by the wasps is unknown, but Lloyd Dosdall, an entomologist with Alberta Agriculture, says the parasite is having some effect on the crop pest.
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“Cabbage seedpod weevil larvae are already munching their way out of the seedpods of Polish canola and are on the ground. … It is a tough pest to kill, because the window to spray is so narrow.”
The seedpod weevils lay single eggs in canola seedpods. The resulting larvae eat the developing seeds. Female wasps find the larva within a pod, immobilize the larva and lay a single egg onto it. The wasp larva eats its host, eventually consuming all but the head.
The cabbage seedpod weevil is moving farther north each year. This season marks its arrival in the parkland region, with the pest being found in traps near North Battleford, Sask.
“It has made its way into the canola belt,” said Owen Olfert of Agriculture Canada in Saskatoon.
“This is what we’ve been dreading and it’s finally happened. But we’re happy to see that it has its own pests and they aren’t far behind though.
“It’s kind of like the wheat midge and its parasites. As it moved across Western Canada, the parasites of the midge were just a year behind.”
Dosdall said little is known about the tiny wasps, but they appear similar to wasps that attack the cabbage seedpod weevil in Idaho, where they can reduce weevil populations by up to 30 percent.
The wasps were first found in southern Alberta in 2000.
“They’re a gorgeous little thing, with little tiny deer-like antlers,” Dosdall said. “We think the antlers are used for smelling or sensing the location of the weevil larvae in the seedpod, but beyond that we know little about them.”
Entomologists in Alberta and Saskatchewan are harvesting seedpod weevil-infested plant material and placing it in cages.
They expect to see wasps hatching out into the cages and hope to begin studying them for clues about how to increase their numbers in hopes they may be used to control seedpod weevil populations.
Droughts of the past few years in central Alberta and western Saskatchewan slowed the northern spread of the weevils, but with a return to better growing conditions, the crop pest will soon be a part of the management strategy for all canola producers in Western Canada, say entomologists.
