Pests & Predators, Ep 9: Secret agents in the stubble


There are secret, mysterious agents lurking in crop stubble. But have no fear, they’re on your side.

Many are familiar with wheat midge and the damage the insect can cause, but you might be less familiar with the parasitoid that attacks this crop pest.

Host Shaun Haney is joined by Jennifer Otani, pest management biologist with Agriculture and Agri-Food Canada at Beaverlodge, Alta., for this chat on wheat midge and its parasitoid in this latest Pests & Predators podcast episode.

Wheat midge on a head (AAFC/Supplied)

During routine canola surveys in the Peace River Region starting in 2013, including looking at surface wheat stubble under canola, Otani and her team found hundreds of very small parasitoid wasps. Otani’s suspicions were confirmed after sending the wasps away to Ottawa: they were Macroglenes penetrans.

“This is a very effective parasitoid wasp, that was actually introduced in Saskatchewan in the 80s, to actually combat wheat midge,” says Otani. This parasitoid wasp is very host specific and will attack wheat midge by laying its egg inside the wheat midge egg, so that when the wheat midge hatches and develops, the parasitoid is inside the developing wheat midge larvae.

Otani explains that wheat midge overwinter in cocoons, that enclose last year’s larvae and contain the parasitoid wasp, for the appropriate spring conditions to emerge.

“When we did our annual canola sweeps, and when we were in fields that had wheat stubble, we found some huge numbers of Macroglenes penetrans,” says Otani. “What we very much suspect is happening is that they’re actually up on the flowering canola, feeding on nectar and maybe pollen — and that’s very typical for our parasitoid wasps — they’re possible even mating, and from that point they then disperse to find the wheat fields and the wheat midge.”

For growers in the Peace River region, it means a viable beneficial parasitoid of wheat midge that Otani and her team are continuously seeing in the area. Macroglenes penetrans are very small, about 1.0 to 1.5 mm long, but one key way to identify the levels of parasitism is through the Alberta Agriculture coordinated soil core survey, says Otani, which provides the data for forecasting maps of wheat midge.

Macroglenes penetrans (AAFC/Supplied)

Otani advises growers to operate on the assumption that if they’ve had wheat midge in their wheat in the past, they may have some levels of the parasitoid wasp.

A wheat midge tolerant variety of wheat isn’t completely immune to wheat midge, it will still allow a small number of the pest to establish on the blended cultivar. What little population of wheat midge that establishes will become a target of the parasitoid, which has been a proven management plan in Saskatchewan, says Otani.

The wheat midge forecast maps for this coming year for Alberta and Saskatchewan show some red areas, which isn’t great news, but as Otani says, a lot can happen in the spring to affect those wheat midge cocoons. The monitoring maps, based on pheromone trap data that come out later in the season will give up-to-date information.

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