Pests & Predators Podcast, Ep 16: Parasitoids prey on pests in pulses

(Lara de Moissac/RealAgriculture)

Usually a pest of canola, but sometimes a pest of faba bean and other pulses, the bertha armyworm is a significant eater of crop yield in Canada.

For this episode of the Pests & Predators podcast, brought to you by Field Heroes powered by the Western Grains Research Foundation, host Shaun Haney discusses a fascinating predator of bertha armyworm with Alberta Pulse Growers’s Nevin Rosaasen.

The bertha’s most common predator, Banchus flavescens, is easy to distinguish by its distinctive segmented body and a very long ovipositor that looks like a long tail. It is usually a light yellow, but it can come in other colours as well, with shades of orange on the “tail.”

This parasitoid wasp lays its eggs in the first to third larvae stage of a bertha armyworms. The mature larvae are then killed prior to entering the soil to pupate overwinter, so this natural enemy does not destroy the larvae prior to the crop damage occurring, however, it keeps the bertha populations in check. Rosaasen explains this wasp is one of the reason we often we see bertha armyworm impacts limited to two to three years at most (read more below the podcast).

Rosaasen says that determining a dynamic threshold for bertha armyworm — one that accounts for beneficial insect populations — is a work in progress. “We haven’t established dynamic thresholds because it would require a PhD project and years of study, but we’re moving towards saying that if you see this parasitoid insect present that you should limit spraying,” he says. Too often, an insecticide spray might be economic in the short term, but detrimental in the long term to beneficial insect populations.

Courtesy the Government of Manitoba

“There’s nothing like boots on the ground,” Rosaasen says in regards to fully scouting for both pests and predators. Maps, like those from the Prairie Pest Monitoring Network, are helpful and an excellent tool for building pest populations, but identifying and quantifying beneficial insects in the field requires in-person scouting.