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Bertha Armyworm

By James Tansey, PhD AAg, Provincial Insect/Pest Management Specialist, Regina

July 2020

Bertha armyworm adult
Bertha armyworm adult

One of the most important pests of canola in Saskatchewan is bertha armyworm, Mamestra configurata. This insect is native to western North America. Bertha armyworm is considered a climbing cutworm and is in the same family Noctuidae, as other cutworm species. It overwinters as a pupa, emerges as an adult from June to early-August, mates and lays eggs on plants from several families.

Adults (moths) are nocturnal nectar feeders with a wing span of about four cm (1.5 in.). Forewings are predominantly gray with black, brown, olive and white flecks. Near the front of the forewing is a white, kidney-shaped mark. Near the tip of the forewing, there is also a white, wavy pattern.

They are relative generalists and lay eggs on canola, mustard, flax and alfalfa. They have recently demonstrated a preference for quinoa. Females are attracted to flowering plants.

Mature bertha armyworm larvae
Mature bertha armyworm larvae

There is one generation per year. Eggs are laid in clusters of up to 500 on undersides of leaves. Individual eggs aren’t much bigger than a period on this page. These have a distinct, cream-coloured, sculptured look, and hatch in about a week. Young larvae are very small and may fall from leaves, dangling by a silken thread. This can make them difficult to distinguish from diamondback moth larvae. However, diamondback moths wriggle when touched. Young larvae feed on the undersides of leaves and chew irregular holes. This feeding is rarely damaging.

As larvae mature, damage increases. Mature larvae are about four cm (1.5 inch) long. There are many colour morphs ranging from velvety black to light green. However, all are characterized by a light brown head capsule and a broad, yellowish-orange stripe along each side. Mature larvae can damage canola pods through consumption of seeds and damage to the pod surface, contributing to shatter. Heavy damage usually occurs late-July through early-August.

Bertha armyworm pupa
Bertha armyworm pupa

After about six weeks of growth, larvae fall from plants and burrow to depths of five to 16 cm (two to six inches) to pupate. They'll spend the winter in this stage. Pupae are coppery-red, 0.5 to 1.8 cm (0.2 to 0.7 inches) long and may wriggle when touched.

In collaboration with cooperators throughout the province, we're conducting monitoring for bertha armyworm adults with a network of pheromone-baited traps. We post cumulative trap catch maps on the ministry website and through the Prairie Pest Monitoring Network, approximately weekly in the summer. Monitoring for larvae should begin approximately two weeks after regional peak trap catch.

For information on cumulative trap catches view the bertha armyworm map.

For information on economic thresholds and monitoring, refer to the bertha armyworm web page.

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