Week 7: Diamondback Moth

Meghan Vankosky
Insect of the Week

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 AgricultureSaskatchewan 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

Meghan Vankosky
Insect of the Week

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

Meghan Vankosky
Insect of the Week

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

Meghan Vankosky
Insect of the Week

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

Meghan Vankosky
Insect of the Week

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

Meghan Vankosky
Insect of the Week

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

Meghan Vankosky
Insect of the Week

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).