Category: Insect of the Week

Week 1: Welcome to Insect of the Week 2025!

This spring and summer, we will be highlighting insects that might be unfamiliar to you.

They might be insects that have building populations on the prairies, like Hessian fly.

They might be found occasionally in western Canada as migratory pests, like western bean cutworm.

**Adult western bean cutworm. Photographed by Adam Sisson, Iowa State University, bugwood.org**

They might be found in other parts of Canada but not on the prairies, like swede midge.

**An adult swede midge and swede midge larvae developing on a canola plant. Photographed by Jonathon Williams, AAFC-Saskatoon.**

Or they might not yet be found or established in Canada. They could be pests in other parts of the world, like cabbage stem flea beetle, or they could be invasive alien species that we need to watch out for in Canada, like spotted lanternfly.

**A pinned adult spotted lanternfly, showing the distinct patterns and colours of this invasive alien species. Photographed by Bryan Brunet, AAFC-Ottawa.**

Invasive insects and other invasive pests can have significant and negative impacts on agroecosystems and increase the cost of crop production. Managing invasive alien species, including insects, involves: Preparedness, Prevention, Detection, Response and Recovery.

Preparedness, Prevention, and Detection are important steps that can help to keep invasive alien species from becoming established in Canada. Everyone can help to prevent the invasion of insects by following guidelines to avoid the accidental movement or introduction of insects to Canada.

Similarly, everyone can help with early detection of invasive insects. In the Prairie Region, 12 important insect pests to watch out for are included on posters developed by the Canadian Plant Health Council.

There are also posters for three other regions of Canada: British Columbia (EN/FR), Ontario/Quebec (EN/FR), and the Atlantic Region (EN/FR).

In Week 2 we will feature a very high profile invasive alien species: Spotted lanternfly.

Week 16: Wheat Stem Sawfly

The wheat stem sawfly, Cephus cinctus, is native to western Canada. Its hosts include species of native grasses as well as rye, barley, and winter wheat. It is most economically damaging to spring wheat and durum wheat in western Canada.

**An adult wheat stem sawfly. Picture by Dylan Sjolie, AAFC-Saskatoon.**

Adult wheat stem sawfly do not feed; they live for about 10 days and spend that time mating, dispersing to wheat or durum crops, and laying eggs. Larvae are the damaging stage of the wheat stem sawfly life cycle. Larvae feed on pith inside the wheat stems. Because the larvae feed inside the wheat stems, the damage they cause is not obvious or easy to detect.

By feeding inside the host plant stems, wheat stem sawfly can reduce the quality and quantity of the grain produced by their host. In the late summer, the larvae also cut the stems of their host plant when they prepare to overwinter. The cut stems are susceptible to lodging.

In the fall, cut stems are used to estimate the density of wheat stem sawfly in wheat and durum fields using the protocol available from the Prairie Pest Monitoring Network. The results of the survey conducted in fall 2023 indicated that wheat stem sawfly densities were quite high in southern Alberta and south western Saskatchewan. Historical maps of the results of the wheat stem sawfly survey are also available from the PPMN Risk Maps page.

Additional information about the wheat stem sawfly is available from the Saskatchewan Ministry of Agriculture and from Alberta Agriculture and Irrigation. For more information, wheat stem sawfly was featured as an Insect of the Week in 2023 and is included 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).

Week 15: European Corn Borer

European corn borer, Ostrinia nubilalis, is a generalist pest of a variety of crops, including corn, potatoes, beans, sugar beets, tomatoes, quinoa, and millet. European corn borer is an occasional pest of crops in western Canada; as many of its hosts are grown in western Canada, it is important to monitor for European corn borer. In eastern Canada, European corn borer is an important pest and its populations are monitored by the Great Lakes and Maritimes Pest Monitoring Network and by the Réseau d’avertissements phytosanitaires in Quebec.

**European corn borer larva and feeding damage on a plant stem. Picture by Jocelyn Smith, University of Guelph.**

In western Canada, European corn borer has one generation per year. Adult female moths lay eggs in clusters on the underside of leaves in June, July and August. Larvae can typically be found feeding on leaves starting in July. Larval feeding continues until the larvae reach the fifth instar, which overwinters.

**External plant symptoms of European corn borer feeding damage on corn. Picture by Jocelyn Smith, University of Guelph.**

Early instar European corn borer larvae eat the leaves of their host plants. As the larvae grow, they tend to begin feeding on the midrib of leaves and on plant stems by tunneling into these plant structures. In corn, the growing larvae can mine into and feed on the corn tassels. Damage to the leaves and stems caused by European corn borer larvae can cause dieback, especially to young plants. Damage to the stems caused by tunneling larvae can weaken the plants, leaving them prone to breakage during storms or in windy conditions. Damage to the stems also interrupts nutrient cycling in infested plants, which can affect the quality and quantity of yield.

**European corn borer damage to millet. Note the pile of frass (insect feces) in a pile below the affected millet plant. Picture by John Gavloski, Manitoba Agriculture.**

Later instar larvae often begin feeding on the reproductive structures of the host plant: the pods, fruits, or ear shanks. Larval feeding to these structures affects the marketability of the crop; in many crops, including sweet corn and peppers, there is zero tolerance for European corn borer damage.

The Insect Community of Practice, a committee of the Canadian Plant Health Council has developed a harmonized monitoring protocol for European corn borer. This protocol can be used in any of the many crops that European corn borer can infest, not just corn.

For more information, please read the European corn borer page in Field Crop and Forage Pests and their Natural Enemies in Western Canada, also available in French. You can also find information from Manitoba Agriculture, OMAFRA, and the Canadian Corn Pest Coalition.

Week 14: Cabbage White Butterfly

Pieris rapae is known as the imported cabbageworm, the cabbage butterfly, and the cabbage white butterfly. Larvae are green and are covered in short, soft hairs, giving them a velvety appearance. The larvae are the damaging stage of the cabbage white butterfly life cycle. The larvae will eat the leaves and pods of canola and related field crops, but cabbage white butterflies are not considered to be an economic pest of canola.

**A group of larvae of the imported cabbageworm (a.k.a. cabbage white butterfly) feeding inside a broccoli crown. Picture by Meghan Vankosky, AAFC-Saskatoon.**

The larvae of cabbage white butterflies also consume the leaves of cruciferous weeds and vegetables, like broccoli, cabbage, and rutabaga. In vegetables, feeding damage to the leaves results in jagged holes.

A broccoli plant in a backyard garden with jagged holes in the leaves caused by cabbage white butterfly larvae. At least two larvae are also visible in the picture. Picture by Meghan Vankosky, AAFC-Saskatoon.

Larvae can also tunnel into the heads of vegetables, as pictured below. The combination of feeding damage to the heads and build-up of frass (fecal matter) can affect the marketability of vegetables infested with cabbage white butterfly larvae.

A broccoli crown with two holes in the head where larvae of the cabbage white butterfly tunneled into the center of the crown. The larvae pictured above were found feeding inside this broccoli crown. Picture by Meghan Vankosky, AAFC-Saskatoon.

Adult cabbage white butterflies do not damage crops as they feed on nectar. The white butterflies have black-tipped forewings with black spots and are often seen flying around canola and mustard fields and around gardens where cruciferous vegetables are grown. In 2023, cabbage white butterflies were especially numerous in southeastern Saskatchewan in August.

**An adult cabbage white butterfly. Picture by David Cappaert, bugwood.org.**

For more information, please read the Imported Cabbageworm page in Field Crop and Forage Pests and their Natural Enemies in Western Canada, also available in French, or check out the cabbageworm page in the Canola Council of Canada Canola Encyclopedia.

Week 13: Canola Flower Midge

Canola flower midge overwinter inside cocoons in the soil and adults usually begin to emerge in late June and can be found until late August, so long as canola flowers are available. There are likely two generations per year, but emergence of adults also seems to be relatively unsynchronized and may not always occur in distinct peaks that align with discrete generations. Canola flower midge adults are not damaging to their host plants. The presence of adult canola flower midge can be detected using pheromone-baited traps.

**A canola flower with canola flower midge larvae developing inside. Picture by Jon Williams, AAFC-Saskatoon.**

Adult female canola flower midge lay their eggs on developing canola buds before they bloom. The larvae develop in groups inside the flower, resulting in a galled flower that does not produce a pod.

**Galled flowers, resulting from larval feeding by canola flower midge on a canola raceme. Picture by Boyd Mori, University of Alberta.**

Galled flowers can occur at any point along a canola raceme, with early emerging adults laying eggs on the first flowers to open. The galled flowers tend to remain ‘stuck’ on the raceme, even after the larvae have dropped to the soil to pupate. A monitoring protocol for canola flower midge, based on galled flowers can be used to estimate population densities in canola fields.

**A canola raceme with galled flowers (circled), caused by canola flower midge in the field. Picture by Boyd Mori, University of Alberta.**

Canola flower midge was described in the scientific literature in a paper published by Mori et al. in 2019, after its identify was confirmed in 2016. There is still a lot to learn about canola flower midge, including its potential to have economic impacts on canola yield.

Please read more about canola flower midge in previous Insect of the Week posts published in 2018 and 2021 or visit the Canola Council of Canada Canola Encyclopedia for more information about canola flower midge.

Week 12: Swede Midge

To the very best of our knowledge, swede midge are NOT currently present in western Canada.

**Adult and larval swede midge on a growing point of a canola plant; note the characteristic purpling of the infested growing point. Picture by Jon Williams, AAFC-Saskatoon.**

Every year, the Prairie Pest Monitoring Network coordinates a pheromone-based monitoring program for swede midge because of the high risk that swede midge poses to the canola industry in western Canada. Swede midge is also a threat to the vegetable industry in western Canada, as it can use broccoli, cabbage, cauliflower, and other crucifer vegetables as a host.

Adult swede midge do not damage canola or crucifer vegetables, but females lay eggs on the growing points of the plant. When eggs are laid on the florets of canola, some flowers on the raceme may develop normally, but the others become ‘fused’ together as a result of swede midge larval feeding.

**Flower buds ‘fused’ together on a floret, the result of infestation by swede midge. Picture by Jon Williams, AAFC-Saskatoon.**

Female swede midge can also lay eggs where new racemes or branches grow off the main stem of canola plants. In this situation, larval feeding stops the growth of the new raceme, leaving a stunted raceme with crumpled leaves that often turn purple.

**Crumpled and purple-coloured new growth on a canola plant, as in the circled part of the picture, is a symptom of infestation by swede midge. Picture by Meghan Vankosky, AAFC-Saskatoon.**

In vegetable crops like broccoli, cauliflower, and cabbage, larval feeding on the growing point of the plant prevents development of the harvestable heads. Very high yield losses have been observed in eastern Canada and the eastern United States in vegetable crops because of swede midge damage.

So far, swede midge is not an established pest in western Canada and we have not found it in pheromone traps in 10+ years of monitoring in Alberta, Saskatchewan, or Manitoba. But, swede midge is slowly moving farther and farther west in the United States. To protect the canola and vegetable industries in western Canada, it is very important to be vigilant and continue to monitor for swede midge.

If you find damage on canola or crucifer vegetable crops that looks like it could be swede midge damage, please report it. You can email meghan.vankosky@agr.gc.ca with pictures or questions.

Please visit the Canola Council of Canada Canola Encyclopedia for more information about swede midge. You can find additional information in previous Insect of the Week posts and in Field Crop and Forage Pests and their Natural Enemies in Western Canada (also available in French).

Week 11: Lygus Bugs

The Lygus bug pest complex includes at least 5 species, including the tarnished plant bug (Lygus lineolaris), Lygus keltoni, and Lygus borealis. Lygus bugs have an upside down triangle on their backs and adults are about 5-6 mm long; their colour varies depending on the species and their stage of development. Lygus bugs have a fairly wide host range, but canola, soybean and alfalfa are prone to yield losses resulting from Lygus feeding damage.

**An adult *Lygus* bug, with the characteristic triangle on the back. Picture by AAFC-Saskatoon.**

*Lygus* nymphs of different instars and an adult *Lygus* bug. Pictures by Hector Carcamo, AAFC-Lethbridge.

The nymphs and adults use piercing and sucking mouthparts to drink from their host plants. They prefer to feed on new growth and reproductive tissues, as these are more nutrient-rich than other plant structures. Feeding by Lygus bugs can result in bud-blasting, where developing buds or flowers do not continue to develop and drop from the plant. If Lygus bugs feed on developing seeds, the seeds become shriveled, reducing yield quality and quantity. Watch for circular, black scars on canola pods, as these are an indicator that Lygus bugs has been feeding on canola pods, and probably on the seeds inside the pods.

Top: A canola raceme with bud blasting symptoms typical of *Lygus* feeding injury. Bottom: Canola seeds damaged by *Lygus* feeding (left, middle) and healthy canola seeds (right). All pictures by R.A. Butts, AAFC-Lethbridge.

In addition to direct yield losses due to Lygus feeding damage, the wounds left by their mouthparts make plant tissues vulnerable to infection by pathogens. Because Lyugs bugs inject digestive enzymes into the plant to help break down plant tissues for consumption, they can also vector plant diseases.

Use a sweep net to scout for Lygus bugs in canola and alfalfa crops. The PPMN has a monitoring protocol available here.

In canola, scout as flowering is complete and pods are beginning to ripen. Take 10 sweeps at 15 locations in the field and estimate the number of lygus nymphs and adults per sweep. Recent research suggests that the economic threshold to avoid yield loss in canola is 2-3 Lygus bugs per sweep; check out the Canola Council of Canada, Manitoba Agriculture, and Alberta Agriculture and Irrigation Lygus pages for more information about Lygus bugs and economic thresholds in canola.

In alfalfa, scout at the start of the bud stage by taking 5 sweeps in at least 15 locations per field and estimating the number of Lygus nymphs and adults per sweep. In seed alfalfa fields, the economic threshold is 8 Lygus per sweep in at least 40 sweeps.

For more information about Lygus bugs, visit previous Insect of the Week articles and find the Lygus page in Field Crop and Forage Pests and their Natural Enemies in Western Canada, available in English and in French. SaskPulse also recently published an overview of Lygus impacts on pulse crops written by Jennifer Bogdan.

Week 10: Cabbage Seedpod Weevil

Cabbage seedpod weevil, Ceutorhynchus obstrictus, is an invasive alien insect. Cabbage seedpod weevil is present in Alberta, Saskatchewan and Manitoba but it has not yet been detected in the Peace River region. Both the adult and larval stages of cabbage seedpod weevil feed on canola, brown mustard, and wild mustard. Feeding by the larvae generally has a greater impact on crop yields than feeding by the adults.

**A dead adult cabbage seedpod weevil, posed for a picture by Jon Williams, AAFC-Saskatoon.**

Cabbage seedpod weevil larval feeding results in direct yield loss because the developing larvae consume developing canola and brown mustard seeds inside the pods. Each larva can eat up to 5 seeds during its development. In addition to the direct yield loss caused by the larvae, pods infested by cabbage seedpod weevil are more likely to shatter during harvest and are prone to secondary infection by fungal pathogens.

**A cabbage seedpod weevil larva inside a canola pod, where it developed by consuming canola seeds. Picture by AAFC.**

Adult cabbage seedpod weevil will feed on a variety of brassica species, both crops and weeds, but does not use yellow mustard as a host plant. In spring, adult cabbage seedpod weevil can be found feeding in patches of flix weed, hoary cress, stinkweed, and volunteer canola. The adults then disperse into canola and brown mustard crops, where they eat flower buds and flowers. This feeding damage can result in bud-blasting, but does not typically impact crop yields. The new generation of cabbage seedpod weevil adults that emerge in late summer can also feed on pods before the crops are harvested.

**Exit holes in canola pods that were chewed by cabbage seedpod weevil larvae. Larvae exit the pods to pupate in the soil once larval development is completed. Picture by AAFC.**

Scout for adult cabbage seedpod weevil as they disperse into canola fields and prepare to lay eggs. When scouting, take ten 180° sweeps at ten locations in the field. Count the adult weevils after each set of 10 sweeps and calculate the average number of adult cabbage seedpod weevil per sweep. Carcamo et al. published new research about cabbage seedpod weevil in 2019, where they found that the economic threshold for cabbage seedpod weevil is 2.5-4 adult weevils per sweep.

The Canola Council of Canada, Alberta Agriculture and Irrigation, and Saskatchewan Ministry of Agriculture have more information about cabbage seedpod weevil and excellent pictures of the damage caused by cabbage seedpod weevil.

For more information about cabbage seedpod weevil, visit previous Insect of the Week articles and find the cabbage seedpod weevil page in Field Crop and Forage Pests and their Natural Enemies in Western Canada, available in English and in French.

Week 9: Wheat Midge

Wheat midge, Sitodiplosis mosellana, is an important pest of spring wheat, winter wheat, durum wheat and triticale. Spring rye can also experience some damage from wheat midge. Adult wheat midge do not damage their host plant, but do lay eggs that give rise to the damaging larval stage.

Wheat midge larvae feed on the outside of wheat kernels. Larval feeding results in shrunken, shriveled, and/or cracked kernels. Larval feeding can also cause kernel development to be aborted.

Feeding damage caused by larval wheat midge reduces grain yield and the quality of the harvested grains. Grains with wheat midge damage are typically downgraded at the grain elevator.

Wheat midge damage to the kernels is not easy to detect and can go unnoticed. Therefore, scouting for adult wheat midge is necessary to determine if foliar insecticides may be needed to prevent female wheat midge from laying eggs. Scout for adults in the evenings, daily during the susceptible plant stage. Calm evenings are best for scouting. Count the adults on 4-5 wheat heads at 5 locations in the crop to estimate midge per wheat head. Economic thresholds are:

>1 wheat midge per 4-5 wheat heads (to prevent yield loss)
>1 wheat midge per 8-10 wheat heads (to prevent grade reduction)

For more information about wheat midge, please visit the Prairie Pest Monitoring Network’s Risk Maps page to see annual wheat midge survey results, and previous Insect of the Week posts about wheat midge and its parasitoid, Macroglenes penetrans. Alberta Agriculture and Irrigation, Saskatchewan Ministry of Agriculture, and Manitoba Agriculture also have great wheat midge information resources and you can find information about wheat midge in Field Crop and Forage Pests and their Natural Enemies in Western Canada (also available in French).

Week 8: Bertha Armyworm

During bertha armyworm outbreaks, canola and mustard crops typically experience the most damage and highest economic losses. However, bertha armyworm also eat alfalfa, peas, quinoa, flax, potatoes, and other crop and weed plants. Adult moths do not damage crops. Larvae consume green plant tissues using their chewing mouthparts.

**A canola field stripped of leaves and with damage to pods following a severe infestation of bertha armyworm in Manitoba. Picture by John Gavloski, Manitoba Agriculture.**

Bertha armyworm larvae are cause for concern when they occur in high numbers when canola pods are developing and maturing. This is because ‘mature’ bertha armyworm larvae (e.g., 5^th and 6^th instars) will start eating developing canola pods. Pod damage includes debarking, which can result in pod shatter before or during harvest. Bertha armyworm larvae can also directly consume the developing seeds. Bertha armyworm larvae can also clip flowers and bolls off of flax plants.

**A bertha armyworm caterpillar in the process of feeding on a canola pod. Picture by John Gavloski, Manitoba Agriculture.**

**Bertha armyworm damage, caused by larvae, to canola pods. Picture by Shelley Barkley, Alberta Agriculture and Irrigation.**

The Prairie Pest Monitoring Network, Alberta Agriculture and Irrigation, Saskatchewan Ministry of Agriculture and Manitoba Agriculture coordinate an annual monitoring program for bertha armyworm using pheromone traps. The 2024 monitoring season started the week of June 10 and will continue until late July. Thank you to all of the volunteers across the prairies who are hosting bertha armyworm pheromone traps!

The number of bertha armyworm moths captured in the pheromone traps serves as an estimate of local risk. Watch for information about the bertha armyworm monitoring program from the PPMN Weekly Updates and the provincial insect updates. If trap catches indicate possible risk, then scout canola crops for larvae using the bertha armyworm monitoring protocol found on the PPMN Protocol page. Information to calculate economic thresholds can also be found in the monitoring protocol.

The life cycle of bertha armyworm: A) eggs, B) larval stage, C) pupal stage, and D) adult stage. The larval stage is the only stage that actively damages crops. All pictures by Jon Williams, AAFC-Saskatoon.

More information about bertha armyworm is available from the Canola Council of Canada, Alberta Agriculture and Irrigation, Manitoba Agriculture, and the Saskatchewan Ministry of Agriculture. You can also read about bertha armyworm in Field Crop and Forage Pests and their Natural Enemies in Western Canada, available in English and French on the PPMN Field Guides page.

Week 7: Diamondback Moth

Diamondback moth larvae have voracious appetites for canola, mustard, flix weed, and vegetables including broccoli, brussels sprouts, cauliflower, and kale. They are specialists of plants in the family Brassicaceae (formerly Cruciferae).

When diamondback moth larvae first hatch, they are very small and tunnel inside the leaves to eat, resulting in damage that looks like shot-holes and leaf mines.

The life cycle of diamondback moth and damage characteristic of B) first and second instar larvae that tunnel and mine leaves, often leaving ‘shot-hole’ damage, and C) third and fourth instar larvae that can eat entire leaves, except for the leaf veins. All pictures taken by Jon Williams, AAFC-Saskatoon.

Third and fourth instar larvae are larger and can consume entire leaves, leaving just the leaf veins. Larvae will also eat the buds, flowers and developing pods. Later in the growing season, as canola matures, diamondback moth larvae can strip the pods of any remaining green tissues.

Damage caused to a canola plant in a colony of diamondback moth maintained at AAFC-Saskatoon. This is an extreme example of the capacity of diamondback moth larvae to strip all green material from the stems, leaving a skeletonized plant with a frosted appearance. **The picture also shows how frass (fecal material) can accumulate on the remaining plant tissues. Picture by Meghan Vankosky, AAFC-Saskatoon.**

In addition to feeding damage, frass (or fecal material) excreted by diamondback moth larvae can affect the marketability and the quality of crucifer vegetables like broccoli, cauliflower, cabbage and brussels sprouts by contaminating or staining the developing vegetable heads.

Remember that the diamondback moth can have multiple generations per year and that each generation takes about 18-20 days (but can be shorter or longer depending on temperature). With each generation, there is potential for the population density to grow and exceed economic thresholds. Scout for diamondback moth by examining plants for larvae and estimate the number of larvae per m² to determine if the population is nearing or has exceeded the economic threshold.

In canola, the economic threshold for diamondback moth larvae is 100-150 larvae/m² when canola plants are immature and flowering. The threshold is 200-300 larvae/m² when canola plants are mature.

Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network.

Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.

Week 6: Grasshoppers

Grasshoppers have mouthparts designed for chewing. Grasshopper nymphs and adults efficiently consume host plant foliage using their chewing mouthparts. During serious outbreaks, grasshoppers can strip all leafy material off the host plant stems and can also be found eating the leaves on shrubs and trees.

**A sweetclover plant stripped of all leaves by grasshoppers. Picture taken by Meghan Vankosky, AAFC-Saskatoon in southern Saskatchewan in late summer 2023.**

Feeding damage caused by first and second grasshopper instars is less obvious than the damage caused by more mature nymphs and adults, simply because of their differences in size. As a result, the economic threshold used to make management decisions for grasshoppers can change as grasshopper populations mature. Dr. James Tansey has compiled economic thresholds for grasshoppers of different stages attacking different crops.

Feeding damage caused by different grasshopper stages on the leaves of cereal plants. Two-striped grasshoppers were common at this location, near Langham, Saskatchewan in July 2023. Picture by Meghan Vankosky, AAFC-Saskatoon.

The four primary pest grasshopper species differ slightly in terms of their preferred hosts. For example, the clearwinged grasshopper (Camnula pellucida) prefers cereals and some succulent grasses, but tends to avoid broad-leaf species. The two-striped grasshopper tends to show a preference for more ‘lush’ hosts, including broad-leaf species like alfalfa and various pulse crops, as well as cereals and grasses.

The migratory grasshopper has a wide host range and can clip pods and grain heads on maturing crops to find green tissues to eat.

**Grasshopper feeding damage on wheat seedlings inside a demonstration cage. Picture by Meghan Vankosky, AAFC-Saskatoon.**

Scout for grasshopper nymphs along roadsides, especially in south-facing ditches, and along field edges using the protocol developed by Prairie Pest Monitoring Network team members and collaborators. Keep in mind that earlier instar nymphs are easier to manage than late instar nymphs and adults. Information is available online about the lifecycle, damage, monitoring, and economic thresholds for pest grasshoppers, including the grasshopper pages in Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide (also available in French from our Field Guides page).

Week 5: Cereal Leaf Beetle

Cereal leaf beetle larvae eat the upper surface of leaves, leaving behind ‘windows’ of missing foliage that can look like white or yellow stripes on the leaves. Wheat is the preferred host of adult and larval cereal leaf beetle, but this pest will also consume barley, oats, rye, millet, wild oats, and other grasses.

In this picture, we see evidence of larval cereal leaf beetle feeding where green material is stripped from the leaf surface. We also see a female *Tetrastichus julis* parasitoid in the process of parasitizing a cereal leaf beetle larva! Picture by Emily Lemke and Karen Shamash, AAFC-Lethbridge.

Feeding damage caused by adult cereal leaf beetle does not typically result in yield loss to the crop. Rather, feeding damage caused by the larvae, especially to the flag leaf, results in lost yield and reduced crop quality.

In western Canada researchers expected cereal leaf beetle to become a widespread and problematic pest. This prediction has thankfully not yet come true, probably mostly due to the efficacy of an introduced parasitoid, Tetrastichus julis. Learn more about the parasitoid in one of the 2023 Insect of the Week posts!

Information about the biology of cereal leaf beetle and how to monitor for it was published by the Government of Alberta. You can also learn more by visiting the cereal leaf beetle page from the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide (available in French here).

Week 4: Pea Leaf Weevil

The pea leaf weevil is now present in Alberta, Saskatchewan, and Manitoba. Learn more about the biology of the pea leaf weevil here and about its distribution across western Canada here.

**An adult pea leaf weevil, *Sitona lineatus*, feeding along the margin of a field pea plant, leaving behind a ‘u’-shaped feeding notch. Picture by Jon Williams, AAFC.**

This insect causes damage to field pea and faba bean crops during the adult stage and during larval development. Adult pea leaf weevil eat the foliage of their host plants, leaving ‘u’-shaped notches along the edge of the leaves.

**A field pea plant with pea leaf weevil feeding damage. Picture by Meghan Vankosky, AAFC.**

Adult pea leaf weevil will also feed on a variety of other legume and pulse crops, including alfalfa, chickpea, and soybean. Most adult feeding on these hosts takes place in early spring before pea and faba seedlings emerge, and again after peas and fabas have been harvested in summer and early fall.

**Faba bean plants with adult pea leaf weevil feeding damage. Picture by Meghan Vankosky, AAFC.**

Pea leaf weevil larvae damage the nitrogen-fixing root nodules on field pea and faba bean plants.

**A root nodule from a field pea plant with damage caused by pea leaf weevil larvae. Areas with damage appear a dark pink colour. Picture by Meghan Vankosky, AAFC.**

Biological and monitoring information related to pea leaf weevil in field crops is posted by the province of  Alberta and in the PPMN monitoring protocol.  Also access the pea leaf weevil page from 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).

Week 3: Wireworms

There are four primary pest species of wireworms on the Canadian Prairies, including Hypnoidus bicolor and the prairie grain wireworm (Selatosomus aeripennis destructor). More information about the primary wireworm pest species can be found in the Guide to Pest Wireworms in Canadian Prairie Field Crop Production (also available in French).

Wireworms are the larval stage of click beetles from the family Elateridae. Click beetles, the adult stage, do not cause damage to crops.

**A cereal field with patchy seedling emergence and stand establishment due to wireworm infestation. Picture by Dr. Haley Catton (AAFC, Lethbridge).**

Similar to cutworms, bare patches in a field can be an early and obvious sign of wireworm infestation in the spring. Patchy crop emergence, as pictured above, results when wireworms consume germinating seeds or feed on the roots and stems of young seedlings, as pictured below.

**Wireworm feeding damage on a faba bean seedling. Picture by Chris Baan.**

Wireworms live in the soil, where it can take 4 or more years to complete larval development. In the soil, wireworms feed on germinating seeds and the roots of a wide variety of prairie field crops including cereals, pulses, oilseeds, and vegetables including potato and carrots. Damage to root vegetables can result in unmarketable produce.

**Carrots with damage caused by wireworms. Picture by Dr. Haley Catton (AAFC, Lethbridge).**

It is common to use baits to scout for wireworms. Baits, consisting of cut potato pieces or soaked mixtures of oatmeal and other seeds, should be buried 5-10 cm deep at 10 or more locations in unplanted fields in the spring to determine if wireworms are present before planting. Leave the baits for 2 weeks and then dig up the baits to look for wireworms. In fields with patchy seedling emergence, soil sampling can be used to look for wireworm larvae and to determine if the damage is being caused by wireworms or by another pest (like cutworms).

More information about wireworm biology, monitoring and management is available from Manitoba Agriculture, from Alberta Agriculture and Irrigation and in Field Crops and Forage Pests and their Natural Enemies in Western Canada (also available in French).

Week 2: Flea Beetles

The striped flea beetle and crucifer flea beetle are two of the most important pests of canola (and other Brassicaceae) in western Canada, especially early in the growing season. Adult flea beetles spend the winter sheltered under leaf litter, generally along field margins. In spring, adults disperse into crop fields to eat, mate, and lay eggs. For more information about the biology of flea beetles, click here.

**‘Shot hole’ feeding damage caused by flea beetles on the cotyledons and first true leaves of a canola seedling. Picture by Ruwandi Andrahennadi, AAFC-Saskatoon.**

Flea beetle feeding damage has a characteristic ‘shot-hole’ appearance on the cotyledons, as pictured above. Flea beetle feeding damage can also be observed on the first true leaves (also with a ‘shot-hole’ appearance) and on the stem and growing point of the seedlings.

A striped flea beetle feeding on the stem of a leaf. Excessive feeding on the stems of young seedlings can cause stems to break or plants to wilt and if severe, could kill the seedlings. Picture by Ruwandi Andrahennadi, AAFC-Saskatoon.

To scout for flea beetles, examine seedlings for the characteristic ‘shot-hole’ feeding, starting at the field margin. Scout often, as flea beetles can move into fields quickly. The action threshold for applying foliar insecticides for flea beetle is met when 25% of the cotyledon area has been eaten. Visit the Canola Council of Canada Canola Encyclopedia for tools to help estimate defoliation by flea beetles.

Flea beetles can also cause damage later in the summer when the new generation of flea beetles emerges and are looking for food before winter. The feeding damage looks the same as the damage in the spring. High densities of flea beetles feeding on plants late in the season can cause plants to ripen prematurely and feeding damage on pods can contribute to yield loss via pod shatter.

**Drying and desiccated leaves of rutabaga in late summer at Outlook, Saskatchewan, following a severe infestation of new generation flea beetles. Picture by Meghan Vankosky, AAFC-Saskatoon.**

Week 1: Cutworms

Insect of the Week 2024

Welcome back to the Prairie Pest Monitoring Network Insect of the Week! In 2024, the Insect of the Week theme is “What is eating my crop?” All of the Insect of the Week posts will focus on the damage that insects pests cause to their host plants. In many cases, insect feeding damage is characteristic of certain pest species and can help to identify the insect pest or narrow down the list of suspects.

Cutworm Damage

Numerous species of cutworms can cause economic damage to crops in western Canada, including pale western cutworm (Agriotis orthogonia) and redbacked cutworm (Euxoa orchrogaster). Because there are so many species of cutworms, cutworms are an important pest complex, with quite diverse life histories, preferred host plants, and damage symptoms.

All cutworm species undergo complete metamorphosis during their lifetime, progressing through four stages: egg, larva, pupa, and adult. The larval stage is responsible for damage to crops and forage plants. Several cutworm species overwinter as larvae in western Canada, including army cutworm (Euxoa auxiliaris), dusky cutworm (Agrotis venerabilis), and glassy cutworm (Apamea devastator). Therefore, there might already be larval feeding activity happening where these species are present.

**A cereal field with patchy crop establishment due to cutworm infestation (picture courtesy of AAFC)**

There are three primary types of feeding behaviour used by larval cutworms:

1) Subterranean larval feeding, where larvae cut the main stem and consume the foliage by pulling it underground. These larvae are almost never seen out of the soil. The glassy cutworm is an example of a subterranean cutworm. Bare patches in crops, as pictured above, can be indicative of larval feeding by subterranean cutworms.

2) Defoliation by above-ground and surface-feeding larvae that feed on foliage at night but spend the day hiding under leaf litter or under the soil. The army cutworm is a typical above-ground feeding cutworm; late-instar larvae will eat entire leaves, while young larvae feed along the leaf margins. Damage typical of the black cutworm (Agrotis ipsilon) includes irregularly shaped holes in the leaves and stem cutting.

3) Defoliation by climbing cutworms, where the main stem is not usually damaged but is used by larvae to reach the leaves. Damage to the foliage is similar to that caused by above-ground or surface-feeding cutworms.

For more information about cutworms and the damage that they do, please check out Cutworm Pests of Crops on the Canadian Prairies, available in English and in French. You can also read about cutworms in Field Crop and Forage Pests and Their Natural Enemies in Western Canada (in English or in French).

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

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.

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).

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.

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.

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.

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).