WHEAT STEM SAWFLY: DRY WEATHER COULD LEAD TO POPULATIONS ON THE RISE

Wheat stem sawfly (AAFC)

Native to North America, the wheat stem sawfly is an economic pest depending on spring and durum wheat as its main crop hosts. These insects also target winter wheat, rye, grain corn and barley, in addition to feeding on native grass species. It is interesting to note that wheat stem sawflies do not feed on oat crops, as the plant is toxic to these insects.

Wheat stem sawfly larvae feed on the pith of plant stems, impacting crop yield and quality. As these host plants mature, the larvae travel down the stem to its base, where “V” shaped notches are cut into the stem a little above ground level. These notches leave plants vulnerable to collapsing, at which point nothing can be harvested. Because wheat stem sawflies also breed and develop on native grass species, economic damage is more prevalent around crop margins where these plants crossover.

Wheat stem sawfly larva (AAFC)

Adult wheat stem sawflies are 8–13 mm long with a wasp-like resemblance, due to their black body and yellow legs. Females have an egg-laying organ (an ovipositor) that extends from their abdomen. When resting on plant stems, these insects will point their heads downward. Mature larvae are 13 mm long and resemble whitish worms with brown heads.

Wheat stem sawfly developmental stages (Art Cushman, Bugwood)

Biological and monitoring information related to wheat stem sawflies in field crops can be found on our Monitoring page as well as on provincial Agriculture Ministry pages (Manitoba, SaskatchewanandAlberta). For more information, visit the wheat steam sawfly page in the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien).

PEA APHIDS: A PERSISTENT PROBLEM FOR LEGUME GROWERS

Pea aphid (AAFC)

Native to Europe, pea aphids were discovered in Ontario during the late 1800s and continued west into the Prairie region. True to their name, pea aphids consume legumes like field peas, alfalfa, broad beans, chickpeas, lentils and clover. Overwintering as eggs on perennial legumes like alfalfa and clover, pea aphids reproduce asexually until winged females migrate to summer crop hosts to generate several new generations over the growing season.

Pea aphid damage to peas occurs when the insects feed during the flowering and early pod stage, resulting in reduced crop yield due to delayed seed formation and smaller seed size. In alfalfa crops, pea aphids feed on the stems and expanding leaves, stunting overall plant growth and causing the leaves to yellow. Infested alfalfa is more susceptible to cold damage during the winter months.

Adults are long-legged and pear-shaped, between 3-4 millimetres long. Colour varies between light to dark green, and each antennal segment is tipped with a black band. Pea aphid nymphs have a similar appearance but are somewhat smaller.

Pea aphid adults and nymph (AAFC)

Biological and monitoring information related to pea aphids in field crops can be found on our Monitoring page as well as on the Manitoba Agriculture and Resource Development website. For more information, visit the pea aphid page in the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien).

SWEDE MIDGE AND CANOLA FLOWER MIDGE: DOPPLEGANGER PESTS

In 2016, entomologists on the Canadian Prairies identified a previously unknown species of midge while conducting field experiments in northeastern Saskatchewan. The new midge was described in 2019 and is named Contarinia brassicola Sinclair (Diptera: Cecidomyiidae). It is known unofficially as the canola flower midge, although its host range includes mustard varieties.

Swede midge (Bugwood)

The full extent of the host range of canola flower midge has yet to be studied. Field surveys conducted between 2017 and 2019 found that the canola flower midge is widely distributed in Alberta, Saskatchewan, and Manitoba, with some pockets of higher population densities (i.e., northeastern Saskatchewan). The canola flower midge is morphologically similar to the swede midge: a doppelganger insect that damages the same field crops that canola flower midge does, as well as a variety of cruciferous vegetables (e.g., cabbage, cauliflower, Brussels sprouts) and Brassica weeds. Both species have much in common, but differences in the type of plant damage they inflect can help distinguish between the two.

Canola flower midge damage (AAFC)

Neither insect poses a threat to crops in their adult form, but both species have larvae that cause damage to their host plants. Canola flower midge larvae consume individual canola buds, resulting in characteristic galled flowers. In comparison, swede midge larvae are known to attack and consume plant material at any growing point on their host plants, affecting normal plant development.

Both midge species are quite similar in their physical characteristics. Adults are delicate, 2–5 mm long flies ranging in colour from light brown to grey. These insects have long legs, long beaded antennae and sparse venation on their wings. Larvae grow between 3–4 mm long. Young larvae are semi-translucent when they hatch and turn yellow as they mature.

Biological and monitoring information related to the swede midge in field crops can be found on our Monitoring page. For more information, visit the swede midge page in the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien). For more information on the canola flower midge, check out this publication from the Alberta Department of Agriculture and Forestry, and previous postson the Prairie Pest Monitoring Network website.

DIAMONDBACK MOTHS: UNWANTED VISITORS TO THE CANADIAN PRAIRIES

Diamondback moth (Alberta Agriculture and Rural Development)

Diamondback moths are a migratory invasive species. Each spring, adult populations migrate northward to the Canadian Prairies on wind currents from infested regions in the southern or western USA. Upon arrival to the Prairies, migrant diamondback moths begin to reproduce, resulting in non-migrant populations that may have three or four generations during the growing season. Host plants include canola, mustard and other cruciferous vegetables and weeds.

Diamondback moths lay their eggs on leaves. Hatchling larvae tunnel into the leaves, later emerging to the surface to feed. Damage begins as shot holes and eventually expands to complete skeletonization, leaving only the leaf veins. Larvae also feed on flowers and strip the surface of developing pods and stems. Damage can lower seed quality and crop yield.

Diamondback moth damage (AAFC)

Adults are active moths measuring 12 millimetres long with an 18-20 millimetre wingspan. When at rest, the forewings form a diamond-shaped pattern along the mid-line. Mature larvae are 8-millimetre-long green caterpillars. Terminal prolegs extend backwards, resembling a fork. When disturbed, caterpillars drop towards the ground on a silken thread to avoid harm.

Diamondback moth larva (Alberta Agriculture and Rural Development)

Biological and monitoring information related to diamondback moths in field crops can be found on our Monitoring page as well as on provincial Agriculture Ministry pages (Manitoba, Saskatchewan andAlberta). For more information, visit the diamondback moth page in the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien).