Welcome to Week 8 for the 2025 growing season! This week includes: • Weather synopsis • Predicted grasshopper development • Predicted wheat midge development • Cereal leaf beetle • Wheat head armyworm • Aphids in field crops • Lygus bug monitoring • Cabbage seedpod weevil • Predicted diamondback moth development • Predicted bertha armyworm development • European skipper • Monarch migration • Provincial insect pest report links • Crop report links • Previous posts
Catch Monday’s Insect of the Weekfor Week 8 – This year features lesser-known insect pest species to help producers remain vigilant! Learn more about the Spotted wing drosophila!
Questions or problems accessing the contents of this Weekly Update? Please contact us so we can connect you to our information. Past “Weekly Updates” can be accessed on our Weekly Update page.
Dylan Sjolie, Tamara Rounce, Meghan Vankosky and Jennifer Otani
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Week 8
The seven-day average temperature across the Canadian prairies was slightly above 14 °C from June 16-22, 2025 (Fig. 1). Areas surrounding Winnipeg and Brandon received the warmest average temperatures, while areas around Calgary and Grand Prairie experienced the coolest temperatures. Over the past 30 days, the average temperature across the Canadian prairies was around 15 °C (Fig. 2), which is slightly above the long-term climate normal. Since April 1, 2025, production areas near Lethbridge AB and Winnipeg MB have been the warmest, whereas areas near Grande Prairie AB have been the coolest (Fig. 3).
Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for June 16-22, 2025.Figure 2. Thirty-day average temperature (°C) observed across the Canadian prairies for the period of May 24-June 22, 2025.Figure 3. Growing season average temperature (°C) observed across the Canadian prairies for the period of April 1-June 22, 2025.
The average cumulative rainfall amounts over the last seven days across the Canadian prairies was 25 mm (Fig. 4; June 16 – June 22). Locally, higher rainfall was reported in areas surrounding Calgary and Lethbridge in Alberta plus Kindersley and Rosetown in Saskatchewan; between 70 – 100 mm of rain fell in those areas (Fig. 4). Outside of the areas receiving significant rainfall events in the last 7 days, the cumulative 30-day rainfall remains less than 70 mm for most of western Canada (Fig. 5). Over the growing season (April 1-June 22, 2025), areas surrounding Lethbridge and Calgary AB have received >200 mm of cumulative rainfall, whereas much of Saskatchewan, Manitoba, and the Peace River region have received <100 mm (Fig. 6).
Figure 4. Seven-day average precipitation (mm) observed across the Canadian prairies for the period of June 16-22, 2025.Figure 5. Thirty-day cumulative rainfall (mm) observed across the Canadian prairies for the period of May 24-June 22, 2025.Figure 6. Growing season cumulative rainfall (mm) observed across the Canadian prairies for the period of April 1-June 22, 2025.
Dylan Sjolie, Tamara Rounce, Meghan Vankosky and Jennifer Otani
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Week 8
The grasshopper model was developed for the migratory grasshopper, but closely represents the development of the other primary pest grasshopper species found in the prairie region. The model uses weather from the current growing season to estimate the current status of grasshopper populations, but keep in mind that grasshoppers might not be present in all parts of the prairie region. Field scouting is imperative; the model estimates can be used to help time scouting activities.
The phenology model for grasshopper development on the prairies was developed by Olfert et al. (2021) and is described in: Olfert, O., R.M. Weiss, D. Giffen, M.A. Vankosky. 2021. Modelling ecological dynamics of a major agricultural pest insect (Melanoplus sanguinipes; Orthoptera: Acrididae): a cohort-based approach incorporating the effects of weather on grasshopper development and abundance. Journal of Economic Entomology 114: 122-130. DOI: 10.1093/jee/toaa254
Model simulations were used to estimate the development of grasshoppers as of June 22, 2025. The model outputs predict that grasshopper populations, where present, consist mainly of 2nd and 3rd instar nymphs (Fig. 1). These findings correspond with field observations between Saskatoon and Rosetown, Saskatchewan, on June 20, 2025. Based on the model readings, grasshopper development should be most advanced in areas surrounding Winnipeg in Manitoba, and east of Lethbridge in Alberta.
Figure 1. Predicted grasshopper (Melanoplus sanguinipes) development, presented as average instar, across the Canadian Prairies as of June 22, 2025.
Dylan Sjolie, Tamara Rounce, Meghan Vankosky, Shelby Dufton and Jennifer Otani
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Week 8
The emergence of wheat midge (Sitodiplosis mosellana) needs to be synchronized with the development of wheat heads for successful larval development. One factor that determines the timing of adult wheat midge emergence is spring precipitation. Cumulative rainfall between 25-30 mm in May and June is required for overwintered larval cocoons to complete larval and pupal development in the spring. When cumulative rainfall is below 25-30 mm in May and June, the completion of larval development may be delayed or postponed to future growing seasons, resulting in delayed or erratic adult wheat midge emergence in late June and July.
Cumulative rainfall (May 1-June 22, 2025) across the majority of Prairie growing region now exceeds the threshold (30 mm) required to terminate larval diapause.
The model indicates that, where wheat midge populations are present, larvae continue to move to the soil surface (Fig. 1). Although areas surrounding Saskatoon and Swift Current in Saskatchewan and west of Lethbridge in Alberta show low larval populations at the soil surface, this is likely to change as those areas have now received sufficient rainfall over the past week to trigger emergence from larval cocoons (June 16 – June 22). Model output suggests that pupae should be present in the southwest corner of Saskatchewan, in areas between Edmonton and Calgary in Alberta, and around Brandon in Manitoba (Fig. 2).
Figure 1. Percent of wheat midge larval population (Sitodiplosis mosellana) that has moved to the soil surface across western Canada, as of June 22, 2025.Figure 2. Percent of wheat midge larval population (Sitodiplosis mosellana) that has moved to the soil surface across western Canada, as of June 22, 2025.
Please refer to the historical wheat midge survey maps and particularly the 2024 results. Historical survey information paired with updated predictive model outputs help identify areas at risk of wheat midge damage in 2025.
In-Field Monitoring:When scouting wheat fields, pay attention to the synchrony between flying midge and anthesis. In-field monitoring for wheat midge should be carried out in the evening (preferably after 8:30 pm or later) when the female midges are most active. On warm (at least 15 ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads (Fig. 3). Midge populations can be estimated by counting the number of adults present on 4 or 5 wheat heads. Inspect the field daily in at least 3 or 4 locations during the evening.
Figure 3. Wheat midge (Sitodiplosis mosellana) laying their eggs on a wheat head. Photo: AAFC-Beav-S. Dufton and A. Jorgensen.Figure 4. Macroglenes penetrans, a parasitoid wasp that attacks wheat midge, measures only ~2 mm long. Photo: AAFC-Beav-S. Dufton.
REMEMBER that in-field counts of wheat midge per head remain the basis of the economic threshold decision. Also remember that the parasitoid, Macroglenes penetrans (Fig. 4), is actively searching for wheat midge at the same time. Preserve this parasitoid whenever possible and remember insecticide control options for wheat midge also kill these beneficial insects who help reduce midge populations.
Economic Thresholds for Wheat Midge: a) To maintain optimum No. 1 grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage. b) To maintain yield only: 1 adult midge per 4 to 5 heads. At this level of infestation, wheat yields will be reduced by approximately 15% if the midge is not controlled. Inspect the developing kernels for the presence of larvae and larval damage.
Wheat midge was featured as the Insect of the Week in 2023 (for Wk08). Be sure to also review wheat midge and its doppelganger, the lauxanid fly, featured as the Insect of the Week in 2019 (for Wk11) – find descriptions and photos to help with in-field scouting! Additionally, the differences between midges and parasitoid wasps were featured as the Insect of the Week in 2019 (for Wk12). Remember – not all flying insects are mosquitoes nor are they pests! Many are important parasitoid wasps that regulate insect pest species in our field crops OR pollinators that perform valuable ecosystem services!
Additional information can be accessed by reviewing the Wheat midge pages extracted from the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
The cereal leaf beetle (Chrysomelidae: Oulema melanopus) has a broad host range. Wheat is the preferred host, but adults and larvae also feed on leaf tissue of oats, barley, corn, rye, triticale, reed canarygrass, ryegrass, fescue, wild oats, millet and other grasses. Yield quality and quantity is decreased, if the flag leaf is stripped. Fun fact: Cereal leaf beetle larvae carry their own fecal waste above their body to help protect themselves from predators.
Fortunately, the parasitoid wasp, Tetrastichus julis Walker (Hymenoptera: Eulophidae), is an important natural enemy of cereal leaf beetle larvae. Learn more about this beneficial insect species featured in Week 9 of 2023’s Insect of the Week!
Cereal Leaf Beetle Lifecycle and Damage:
Adult: Adult cereal leaf beetles (CLB) have shiny bluish-black wing covers (Fig. 1). The thorax and legs are light orange-brown. Females (4.9 to 5.5 mm) are slightly larger than males (4.4 to 5 mm). Adult beetles overwinter in and along the margins of grain fields in protected places such as in straw stubble, under crop and leaf litter, and in the crevices of tree bark. They favour sites adjacent to shelterbelts, deciduous and conifer forests. They emerge in the spring once temperatures reach 10-15 ºC and the adults are active for about 6 weeks. They usually begin feeding on grasses, then move into winter cereals and later into spring cereals.
Figure 1. Adult Oulema melanopus measure 4.4-5.5 mm long (Photo: M. Dolinski).
Egg: Eggs are laid approximately 14 days following the emergence of the adults. Eggs are laid singly or in pairs along the midvein on the upper side of the leaf and are cylindrical, measuring 0.9 mm by 0.4 mm, and yellowish in colour. Eggs darken to black just before hatching.
Larva: The larvae hatch in about 5 days and feed for about 3 weeks, passing through 4 growth stages (instars). The head and legs are brownish-black; the body is yellowish. Larvae are usually covered with a secretion of mucus and fecal material, giving them a shiny black, wet appearance (Fig. 2). When the larva completes its growth, it drops to the ground and pupates in the soil.
Figure 2. Larval stage of Oulema melanopus with characteristic feeding damage visible on leaf (Photo: M. Dolinski).
Pupa: Pupal colour varies from a bright yellow when it is first formed, to the colour of the adult just before emergence. The pupal stage lasts 2 – 3 weeks. Adult beetles emerge and feed for a couple of weeks before seeking overwintering sites. There is one generation per year.
Access scouting tips for cereal leaf beetle or find more detailed information by accessing the Oulema melanopus page from 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.
Wheat head armyworm (Lepidoptera: Noctuidae): Dargida diffusa (Walker, 1856) feeds on several grassy-type species including wheat, rye, oats, barley, wild oats, native and forage grasses (although timothy is preferred). Wheat head armyworm overwinter within earthen cells as pupae. Each growing season, there are two generations of adults produced. This means both a spring and summer larval generation occur, however, the first generation can cause damage early in the growing season in wheat and some grasses (Fig. 1) although infestations are very sporadic and rarely reach densities requiring control.
Figure 1. Wheat head armyworm larva (Noctuidae: Dargida diffusa) and frass (larval poop) plus shed larval head capsule where developing kernel formed but was consumed. Photo kindly shared by: B. DeSmet, Dirt Road Agronomy.
Adult moths are 30-38 mm in wing span, are yellowish-brown, but have a chocolate-brown stripe running down the length of each forewing. Larvae have a pale brown head capsule, grow to ~25 mm long, and are bright green or tan with lateral white stripes that help camouflage them on awns (Fig. 2). The previous alternate scientific name for this species was Faronta diffusa. Wheat head armyworm are surprisingly difficult to spot in situ and are sometimes initially detected in sweep-nets (Fig. 3).
Figure 2. Examples of three colour morphs of wheat head armyworm (Noctuidae: Dargida diffusa) on cereals growing in the Peace River region in 2024; note consistent stripe patterning but larval body colour can range from bright green to tan. Photos kindly shared by: B. DeSmet, Dirt Road Agronomy.Figure 3. Green and tan colour morphs of wheat head armyworm (Noctuidae: Dargida diffusa) retrieved in sweep-net sample on August 10, 2020, in wheat growing near Magrath AB. Photo kindly shared by: A. Voss, @Voss_Ag
Infestations are very sporadic. There is no nominal or economic threshold for this species in any of the field crop species listed above. Beneficial insects like the parasitoid wasps within the genus Cotesia will attack wheat head armyworm larvae and, shortly after erupting from the larval host, will form clusters of white cocoons (Fig. 4) that eventually yield new parasitoid wasps which subsequently seek out and attack other armyworms.
Figure 4. Cotesia cocoons spun on wheat awns that presumably erupted from immobile larva of wheat head armyworm (Noctuidae: Dargida diffusa) that has numerous lateral exit wounds. Photo taken August 10, 2020, near Magrath AB and kindly shared by:A. Voss, @Voss_Ag
Distribution records for D. diffusa can be reviewed on the Butterflies of North America website although these records would greatly benefit with sightings in western Canada because the species is established in Alberta (central and in the south east of the Peace River region), in Saskatchewan, and Manitoba.
Biological and monitoring information for this insect pest species is accessible as a wheat head armyworm page within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018). The entire guide is accessible as a free downloadable PDF in either English or French on our Field Guides page.
Aphid populations can quickly increase at this point in the season and particularly when growing conditions are warm and dry. Access the Provincial Insect Pest Report for Wk15 to remain alert to areas and crops suffering from aphid pest pressure.
Figure 1. Pea aphid adults (each 3-4 mm long) and nymph. Photo: M. Dolinski.
Additionally, several aphid pest species are described in the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) which is accessible as a free downloadable PDF in either English or French on our Field Guides page. PDF copies of the individual pages have been linked below to access quickly: • Corn leaf aphid or Rhopalosiphum maidis (Fitch) • English grain aphid or Sitobion (Macrosiphum) avenae (Fabricius) • Oat-birdcherry aphid or Rhopalosiphum padi (Linnaeus) • Pea aphid or Acyrthosiphon pisum (Harris) • Potato aphid or Macrosiphum euphorbiae (Thomas) • Soybean aphid or Aphis glycines (Matsumura) • Turnip aphid or Lipaphis erysimi (Kaltenbach) • Sugar beet root aphid or Pemphigus betae Doane • Russian wheat aphid or Diuraphis noxia (Mordvilko)
Lygus bugs are polyphagous (i.e., feed on plants belonging to several Families of plants) and multivoltine (i.e., capable of producing multiple generations per year). Both the adult (Fig. 1) and five nymphal instar stages (Fig. 2) are a sucking insect that focuses feeding activities on developing buds, pods and seeds. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.
Recent research in Alberta has resulted in a revision to the thresholds recommended for the management of Lygus in canola. Under ideal growing conditions (i.e., ample moisture) a threshold of 20-30 lygus per 10 sweeps is recommended. Under dry conditions, a lower threshold may be used, however, because drought limits yield potential in canola, growers should be cautious if considering the use of foliar-applied insecticide at lygus densities below the established threshold of 20-30 per 10 sweeps.In drought-affected fields that still support near-average yield potential, a lower threshold of ~20 lygus per 10 sweeps may be appropriate for stressed canola. Even if the current value of canola remains high (e.g., >$19.00 per bu), control at densities of <10 lygus per 10 sweeps is not likely to be economical. Research indicates that lygus numbers below 10 per 10 sweeps (one per sweep) can on occasion increase yield in good growing conditions – likely through plant compensation for a small amount of feeding stress.
Figure 1. Adult Lygus lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Figure 2. Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).
Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. In canola, lygus bugs feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.
Scouting tips to keep in mind: Begin monitoring canola when it bolts and continues until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.
Sample the crop for lygus bugs on a sunny day when the temperature is above 20 °C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180 ° sweeps. Count the number of lygus bugs in the net. Sampling becomes more representative IF repeated at multiple spots within a field so sweep in at least 10 locations within a field to estimate the density of lygus bugs.
Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol. Also refer to the Lygus 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. The Canola Council of Canada’s “Canola Encyclopedia” also summarizes Lygus bugs. The Flax Council of Canada includes Lygus bugs in their Insect Pest downloadable PDF chapter plus the Saskatchewan Pulse Growers summarize Lygus bugs in faba beans.
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (Fig. 1; left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (Fig. 1; right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Figure 1. Cabbage seedpod weevil (left) and egg dissected from within a canola pod (right). Photos: the late Dr. Lloyd Dosdall.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (Fig. 1; right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically, a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (Fig. 2; left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod (Fig. 2; right photo, lower pod), feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole (Fig. 2; right photo, upper pod) from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Figure 2. Larva feeding amongst developing seeds within canola pod (left) and larval entrance hole (right photo, lower pod) compared to mature larval exit hole (right photo, uppower pod). Photos: the late Dr. Lloyd Dosdall.
Prairie-Wide Monitoring: The annual cabbage seedpod weevil survey is performed in canola at early flower stages using sweep-net collections. Review the prairie-wide historical survey maps for this insect species. Review the PPMN monitoring protocol although the provinces of Alberta, Saskatchewan, and Manitoba have specific survey protocols for their respective network cooperators. Commercial fields where comparatively higher densities of adult cabbage seedpod weevils were observed in 2024 are highlighted yellow, orange, or red in the geospatial map featured in Figure 3.Areas where historically higher densities of cabbage seedpod weevil were observed in 2024 are worth prioritizing in 2025.
Figure 3. Densities of cabbage seedpod weevil (Ceutorhynchus obstrictus) observed in sweep-net samples retrieved from commercial fields of canola (Brassica napus) grown in Manitoba, Saskatchewan, Alberta, and the British Columbia portion of the Peace River region in 2024.
In-Field Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report field observations and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below as an example; retrieved 2025Jun19 but will be updated with 2025 reports as the season progresses).
Dylan Sjolie, Tamara Rounce, Meghan Vankosky and Jennifer Otani
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Week 8
Diamondback moths (DBM; Plutella xylostella) 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 U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths (Fig. 1) attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
Figure 1. Adult diamondback moth.
Diamondback moths were captured on pheromone traps across western Canada from mid- to late-May in 2025. Once adults arrive, there can be several in-season, non-migrant generations of diamondback moth developing throughout the remainder of the growing season. Warm, dry weather tends to promote rapid development of high-density populations of larvae capable of causing severe damage to host crops, including canola.
As of June 22, 2025, model outputs predict that diamondback moth populations are in the first non-migrant generation (Fig. 2).
Figure 2. Predicted number of in-season generations of diamondback moth (Plutella xylostella) expected to have developed across the Canadian prairies, as of June 22, 2025.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025.
In-Field Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 3) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 3. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 4. Diamondback moth pupa within silken cocoon.
Dylan Sjolie, Tamara Rounce, Meghan Vankosky and Jennifer Otani
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Week 8
The phenology model for bertha armyworm development on the Canadian prairies was developed by Ross Weiss and Owen Olfert. Model simulations were used to estimate development of bertha armyworm as of June 22, 2025.
The model outputs predict that bertha armyworm populations, where present, should consist mainly of adults laying eggs (Fig. 1). Based on the model outputs, populations throughout most of Alberta and Saskatchewan are predicted to be mainly be in the egg stage (as of June 22, 2025). In some areas south of Winnipeg, east of Lethbridge, and northeast of Swift Current, larvae may be present (Fig. 2).
Figure 1. The proportion of the (Mamestra configurata) population that is predicted to be in the EGG stage (% of total population) across the Canadian prairies as of June 22, 2025.Figure 2. The proportion of the (Mamestra configurata) population that is predicted to be in the LARVAL stage (% of total population) across the Canadian prairies as of June 22, 2025.
Figure 3 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 3, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumulative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.
Figure 3. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025. For example, Manitoba Agriculture’s June 19th Crop Pest Report includes Figure 4 with a reminder that other moth species are actively flying now so examine wing colourations and patterning carefully when checking the contents of bertha armyworm pheromone traps! Clover cutworm can be common by-catch in pheromone traps designed to monitor bertha armyworm, but also those designed to monitor true armyworm.
Figure 4. Comparison of diagnostic wing features of three moth species. Images and information all courtesy of Manitoba Agriculture, J. Gavloski who originally included in the June 19, 2025, issue of the Manitoba Crop Pest Update.
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm 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 Field Guides page. Also consider reviewing this 2019 Insect of the Week featuring bertha armyworm and its doppelganger, the clover cutworm!
Jennifer Otani, Shelby Dufton, Shelley Barkley and Amanda Jorgensen (formerly AAFC)
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Week 8
The European skipper (Hesperiidae: Thymelicus lineola) is a diurnal, bright orange butterfly (Fig. 1). The predominantly green defoliating larvae can cause economic levels of damage in timothy. The larvae also feed on other species of grasses and winter wheat.
Figure 1. European skipper (Thymelicus lineola) adults on timothy seed seeds. Photo: S. Dufton, AAFC-Beaverlodge.
There is one generation per year of European skipper but butterfly oviposition or egg laying largely dictates where damage occurs the following summer. Host plants include timothy (Phleum pretense), cocksfoot (Dactylis glomerata), couch or quack grass (Agrophyron repens), perennial ryegrass (Lolium perenne), meadow fescue (Festuca pratensis), orchardgrass (Dactylis glomerata).
Early in July, butterflies feed on nectar, mate, and lay eggs. Females lay vertical rows or “strings” of groups of ~30 eggs on the inside of grass leaf sheaths, seed heads or on the stem of a host plant. By late July, larvae develop within the eggs yet they remain safely enclosed to overwinter inside the egg shell. Eggs can be transferred in both hay and seed as seed cleaning will not remove all eggs. Early the following May, the overwintered larvae emerge from the shell, crawling up growing grass blades to feed. Five larval instar stages cause damage by defoliation of the upper leaves of timothy.
Larvae are leaf-tyers that spin and attach silk ties across the outer edges of leaves to pull them together (Figs. 2-5). The silk ties hold the leaf in a tight furl enclosing the larva within a leafy tube then it moves up and down the tube to feed. The tying behaviour and camouflaged green body (marked longitudinally with two white lines) make larvae hard to locate when scouting. Even larger larvae with their brown head capsules are surprisingly difficult to locate because the larva will lie lengthwise, along the base of the leaf fold yet the larva remains very still until touched. When high densities of European skipper larvae are present, leaf tying goes out the window and larvae feed in more exposed areas, often amidst rapidly disappearing foliage.
Adult wingspans range from 19-26 mm but they have bright brassy orange wings with narrow black borders and hindwing undersides that are pale orange and greyish. Nectar sources for adults include orange hawkweed, thistles, oxeye daisy, fleabane, white clover, red clover, common milkweed.The typical flight season extends from early June to mid-July but will vary regionally with southern parts of the Canadian prairies starting earlier than more northern regions.
Access the Provincial Insect Pest Report for Wk09 for updates for this economic insect pest.
Cultural control strategies for European skipper include separating timothy from nectar sources to avoid attracting adults which will mate then oviposit in the same field. Another strategy is the removal of cut grass or bales.
In terms of chemical control, an action threshold of six or more larvae per 30 cm x 30 cm area is recommended to mitigate losses but emphasis should be placed on scouting and managing early instar larvae. If the need arises, chemical control in timothy involves using a higher water volume (e.g., 300 L H2O/ha) to adequately cover the thicker canopy.
Figure 2. Early instar larva feeding along edge of timothy leaf. Photo: A. Jorgensen, AAFC-Beaverlodge.Figure 3. Larva resting in fold of timothy leaf formed by silken tie. Photo: K. Pivnick. AAFC-Saskatoon.Figure 4. Larval feeding damage and silken ties on timothy leaf. Photo: K. Pivnick, AAFC-Saskatoon).Figure 5. In situ camouflaged larvae and feeding damage in timothy. Photo: S. Barkley.
The European skipper was introduced to North America at least a century ago and has moved west and north in its distribution across western Canada even though its area of origin is recognized as Eurasia and northwestern Africa. The initial report of European skipper in Canada is from 1910 and cites it being imported on contaminated timothy seed near London, Ontario.
Distribution records for T. lineola can be reviewed on the Butterflies of North America website. In western Canada, T. lineola established in parts of Saskatchewan by 2006. In 2008, butterflies were collected near Valleyview, Alberta (Otani, pers.comm.), and in 2015 larvae were observed feeding in the flag leaves of winter wheat near Mayerthorpe, Alberta (2015 Meers, pers. comm.). Specimens confirmed as T. lineola were collected in 2016 near Valleyview, Donnelly, and High Prairie, Alberta (2017 Otani and Schmidt, pers. comm.) with additional specimens confirmed from Baldonnel and Clayhurst, British Columbia in 2021 (2021 Otani and Schmidt, pers. comm.).
The European skipper was the Insect of the Week in 2022 (Wk10).
Track the migration of the Monarch butterflies as they move north by checking the 2025 Monarch Migration Map! A screenshot of Journey North’s “first sightings of adults” map is below (Fig. 1; retrieved 2025Jun25) but follow the hyperlink to check the interactive map.
We also share a screenshot of Journey North’s “first sightings of LARVAE” map is below (Fig. 2; retrieved 2025Jun25).
Jennifer Otani, James Tansey, Carter Peru, John Gavloski, Shelley Barkley and Amanda Jorgensen
Categories
Week 8
Prairie-wide provincial entomologists provide insect pest updates throughout the growing season. Follow the hyperlinks to access their information as the growing season progresses:
MANITOBA’SCrop Pest Updates for 2025 have started! Review a PDF copy of the latest reports released June 26, 2025! • Insect pests named in the June 26th report include true armyworm, alfalfa weevil, thrips, and cereal leaf beetle. The cabbage seedpod weevil survey is set to begin and targets canola fields as they start to flower. • Cumulative 2025 counts of intercepted diamondback moths are updated weekly to provide regional information to producers and guide in-field scouting. • Pheromone-baited trap counts are available for true armyworms in these reports. • Cumulative 2025 counts of intercepted bertha armyworm moths are updated weekly. • Bookmark the Crop Pest Update Index and the insect pest homepage to access fact sheets and more!
SASKATCHEWAN’SInsect pest homepage links to important information! Thanks to J. Tansey with Saskatchewan Agriculture for sharing the following update (as of June 26, 2025): • Peritrechus convivus damage has been reported in canola, and durum. There are no thresholds and no registered control products. Please report populations to Tyler.Wist@agr.gc.ca or James.Tansey@gov.sk.ca Adults are brownish-black seed bugs (link to iNaturalist.ca for images of adults) but nymphs are typically aggregated, have a vividly red abdomen with blackish-brown head and thorax (link to 2022 The Western Producer article for image of nymph). • Substantial rain should bring relief to wheat crops affected by brown wheat mite. • Flea beetle populations are waning as the canola crop develops. • Significant cabbage seedpod weevil populations have been reported in the SW and Central regions • Large numbers of pea aphid have been reported in alfalfa hay with the first cut in several regions of SK. There were reports of poor performance of lambda-cyhalothrin insecticides in pea aphid populations in 2024. In response, we have prepared field test kits to assess sensitivity of pea aphid to the insecticide lambda-cyhalothrin but test kit numbers are limited.
ALBERTA’SInsect Pest Monitoring Network webpage links to insect survey maps, live feed maps, insect trap set-up videos, and more. There is also a Major Crops Insect webpage. Remember AAF’s Agri-News includes insect-related information: • June 23, 2025, issue notes that the 2025 cabbage seedpod weevil survey has started in southern Alberta, containtes links to the CSPW reporting tool, and 2024 survey results. It also notes a report of red turnip beetles in canola. • Diamondback moth pheromone trap live monitoring map for AB – Cumulative counts derived from weekly data are now being generated so refer to the Live map. • Bertha armyworm pheromone trap live monitoring map for AB – Cumulative counts derived from weekly data will be generated so refer to the Live map. • Cabbage seedpod weevil live sweep-net monitoring map for AB – In-field reports are uploaded daily so refer to the Live map. • Wheat midge live sweep-net monitoring map for AB – Cumulative counts derived from weekly data will be generated so refer to the Live map.
