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Insects — The Enemy Of My Enemy Is My Friend

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“The caterpillar lives its life with the organism inside it, the organism eventually chews its way out and causes the death of the host.”

James Tansey

Ph. D student in entomology at the University of Alberta

alberta farmer | stettler

Grain producers can cut down on harmful insects by enlisting the help of predators or parasites that prey on them, says James Tansey, a Ph. D student in entomology at the University of Alberta.

Tansey poke about beneficial insects during a recent session on integrated pest management here.

Diamondback moth infestations generally begin in late May or early June and cause foliar and pod damage in canola.

“The severity of infestations depends a lot on the weather, so when they get here determines how big the populations are going to be,” said Tansey, explaining that the moths come up from northern Mexico or the southern U. S.

Tansey said one of the natural enemies of the diamondback moth is Diadegma insulare, a Central American insect that injects venom and eggs into the diamondback larva.

“You’ve all seen the movie Alien?”, said Tansey. “The caterpillar lives its life with the organism inside it, the organism eventually chews its way out and causes the death of the host.”

Parasitized diamondback moth pupa appear dark and cylindrical and act sluggishly, said Tansey.

Another pest is the root maggot, which attacks brassica crops, including canola. The maggots emerge as adults in late spring and early summer, and lay their eggs on cruciferous plants in the four-to five-week stage. When the eggs hatch, the larvae feed on the root hairs and taproot, which causes plants to wilt.

Root maggots have several natural enemies, but rove beetles are a natural predator. These beetles are good fliers, and can be distinguished by their short wing covers. The beetles are voracious consumers and can significantly reduce maggot populations.

The beetles are both predators and parasitoids, and lay their eggs in the soil. Once the eggs of the rove beetle hatch, the larvae tunnel into the pupa of the maggot and consume it.

Interesting defence

Cereal leaf beetles have a slug-like appearance due to the bag of feces that the beetle carries around to defend itself against parasites and predators.

The parasite which consumes the cereal leaf beetle is tetrastichus julis, and it kills the cereal leaf beetle by injecting eggs and venom into the larvae.

“Parasitoid numbers are increasing all the time and they seem to be having an effect on populations. The cereal leaf beetle seems to be effectively controlled in large portions of its range in the U. S. by the parasitoid. There are deliberate efforts to move the parasitoid around to effect control,” said Tansey.

The parasitoid that feeds on the wheat midge egg is a wasp known as macrogenes penetrans. This bug injects its own eggs and venom into the wheat midge eggs. Once the larva of the wheat midge hatches, the parasitoid continues to develop inside it. It takes a lag time of about one year before the

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parasite can completely attack the wheat midge. Agriculture Canada has already researched this parasitoid and estimated that it saved losses of $30 million to Saskatchewan farmers in 1999, said Tansey.

Lacewings are a predacious insect with large jaws and lacey wings. They are predatory generalists and will consume aphids, insect eggs and the larvae of diamondback moths and bertha armyworms. Other predatory insects that consume pests include ladybird beetles and carabid beetles.

Tansey said populations of beneficial insects can be enhanced if producers choose vigorous varieties and maintain proper nutrient regimes. Seeding densities and row widths can also affect pest insects and their predatorsm and can reduce reliance on insecticides. Monitoring crops and populations is also key. “Monitor, monitor, monitor, that’s extremely important,” said Tansey. “Get out there and see what’s going on.”

About the author


Alexis Kienlen

Alexis Kienlen lives in Edmonton and has been writing for Alberta Farmer since 2008. Originally from Saskatoon, Alexis is also the author of two collections of poetry, a biography, and a novel called "Mad Cow."



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