2023 Week 5 (Released June 8, 2023)

Insect scouting and monitoring season is getting into full swing!

Weather patterns in May and so far in June have been perfect for the development of some insect pests, but suboptimal for others. However, it is hard to generalize, as some parts of the prairies have been wet and others dry. Similarly, some areas have been very warm, while others have been cooler. This year it will be very important to scout and to monitor insect populations at the field-scale.

Grasshoppers thrive in warm, dry conditions. This week, some 4th instar nymphs were spotted in ditches in southwestern Saskatchewan, although there are many first, second and some third instar nymphs as well. Signs of damage are starting to appear. Overall grasshopper development continues to be ahead of schedule and two-striped grasshoppers continue to be prevalent.  

Diamondback moths that arrived in early May have likely reproduced and adult moths found now could be from the first generation produced on the prairies. Diamondback moths develop rapidly when it is warm and their population densities can build up quickly with each generation. Be ready to scout if pheromone traps in your area have detected diamondback moths this spring.  

Bertha armyworm development is also well ahead of schedule – pupal development could be 90% complete in some areas and adult moths could already be flying around. Watch the provincial websites in Alberta, Saskatchewan, and Manitoba for reports on bertha armyworm pheromone trap captures for your area over the next few weeks.

This week, the Insect of the Week featured ground beetles and rove beetles! Both can prey on different life stages of the pea leaf weevil and on other insect pests (and slugs!).

 Please read this week’s posts in the Weekly Update for more information about the insects listed above and for a sneak peak of wheat midge development!

Remember, insect Monitoring Protocols containing helpful insect pest biology, how and when to plan for in-field scouting, and economic thresholds to help support in-field management decisions. All are available to read or download for free!

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Questions or problems accessing the contents of this Weekly Update? Please contact Dr. Meghan Vankosky (meghan.vankosky@agr.gc.ca) to get connected to our information. Past Weekly Updates, full of information and helpful links, can be accessed on our Weekly Update page.

Weather synopsis

Average prairie temperatures continued to be well above average from May 29 to June 4. The prairie average daily temperature was 5°C warmer than normal (Fig. 1). The warmest temperatures were observed across southern Manitoba and southeastern Saskatchewan. The coolest temperatures occurred in the Peace River region where temperatures in northwestern Alberta and northeastern British Columbia were similar to climate normal temperatures.

Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for the period of May 29 to June 4, 2023. 

Average temperatures over the past 30 days (May 6 to June 4, 2023) have been 4°C above normal with the warmest values being reported across Manitoba and Saskatchewan (Fig. 2). Average temperatures (30-day) ranged from 13.9°C at Grande Prairie, Alberta to 18.4°C at Morden, Manitoba.

Figure 2. 30-day average temperature (°C) across the Canadian prairies for the period of May 6 to June 4, 2023. 

Since April 1, the 2023 growing season has been coolest across eastern Saskatchewan and western Manitoba (Fig. 3). Alberta temperatures continue to be above average. Relative to climate normals, temperatures continue to be above average in the Peace River region.  

Figure 3. Growing season average temperature (°C) observed across the Canadian prairies for the period of April 1 to June 4, 2023. 

Seven-day cumulative rainfall was nominal for most of Alberta and Manitoba from May 29 to June 4. Eastern Saskatchewan reported greater than 40 mm of rain in the last 7 days (Fig. 4). Coronach, Saskatchewan reported 74 mm and Canora, Saskatchewan had 51 mm in the last 7 days.

Figure 4. Seven-day cumulative rainfall (mm) observed across the Canadian prairies for the period of May 29 to June 4, 2023. 

Saskatchewan has generally had more rainfall over the past 30 days than Alberta and Manitoba (Fig. 5). Saskatchewan has had 85-150% of normal rainfall. Central and southern Alberta and most of Manitoba have had 40-60% of normal rainfall in the last 30 days.

Figure 5. 30-day cumulative rainfall (mm) observed across the Canadian prairies for the period of May 6 to June 4, 2023. 

Growing season rainfall has been lowest in southern Alberta and highest in Saskatchewan and the Peace River region (Fig. 6). Hanna, Alberta has reported only 21 mm of rain since April 1 and Brooks, Alberta has had only 25 mm. In contrast, Assiniboia, Saskatchewan has had 114 mm of rain since April 1, 2023 and Valley View, Alberta has recorded 110 mm.

Figure 7. Growing season cumulative rainfall (mm) observed across the Canadian prairies for the period of April 1 to June 4, 2023. 

Over the past 30 days, different parts of the prairies have been characterized by warm/dry, warm/wet, cool/dry, and cool/wet conditions (Fig. 7). Thus far, locations in southern Manitoba have experienced the warmest and driest growing conditions. The Peace River region has been the coolest and the wettest. Southern Alberta has been the driest and coolest. Many locations in Saskatchewan have had average temperatures and rainfall, although Coronarch is an interesting outlier that has been about average in terms of temperature but also quite wet. 

Figure 7. A scatterplot of prairie locations based on 30-day total rain (y-axis) and temperature (x-axis) for site-specific comparison of weather conditions experienced during the last 30 days of the 2023 growing season (May 6 to June 4, 2023). Graph by Ross Weiss.

Wind trajectory summary

‘Reverse trajectories’ refer to air currents that are tracked back in time from specified Canadian locations over a five-day period prior to their arrival date.  Of particular interest are those trajectories that, prior to their arrival in Canada, originated over northwestern and southern USA and Mexico, anywhere diamondback moth populations overwinter and adults are actively migrating.  If diamondback adults are present in the air currents that originate from these southern locations, the moths may be deposited on the Prairies at sites along the trajectory, depending on the local weather conditions at the time that the trajectories pass over our area (e.g., rain showers, etc.). Reverse trajectories are the best available estimate of the ”true” 3D wind fields at a specific point. They are based on observations, satellite and radiosonde data. 

Relative to the previous two weeks, there was a significant increase in the number of reverse trajectories that entered the Canadian prairies between May 31 and June 6, 2023 (Fig. 1). This week, most of the reverse trajectories that crossed the prairies originated from the Great Plains (Nebraska, Kansas, Texas, Oklahoma). In earlier weeks of this growing season, most of the reverse trajectories originated from the Pacific Northwest. The number of reverse trajectories originating from California and Mexico also significantly increased in the last week. These results may indicate potential introductions of diamondback moth and leafhoppers to the prairies. 

Figure 1. The average number (based on a 5-day running average) of reverse trajectories (RT) that have crossed the prairies for the period of May 8 to June 6, 2023. 

Mexico, California and Texas: This week, 63 reverse trajectories crossed into the prairies from Mexico and the US southwest. These trajectories were predicted to cross into southeastern Saskatchewan and Manitoba (Fig. 2)

Figure 2. Total number of dates with reverse trajectories originating over Mexico, California and Texas that have crossed the prairies between April 1 and June 6, 2023. 

Pacific Northwest (Idaho, Oregon, Washington): This week 104 reverse trajectories were predicted to cross the prairies, with the majority of Pacific Northwest reverse trajectories reported to pass over Alberta and western Saskatchewan (Fig. 3).   

Figure 3. Total number of dates with reverse trajectories originating over the Idaho, Oregon, and Washington that have crossed the prairies between April 1 and June 6, 2023. 

Oklahoma and Texas: In the last week, 98 reverse trajectories that originated over Texas and Oklahoma passed through the prairies, particularly through Manitoba and southeastern Saskatchewan and (Fig. 4). 

Figure 4.  The total number of dates with reverse trajectories originating over Oklahoma and Texas that have crossed the prairies between May 1 and June 6, 2023. 

 Kansas and Nebraska: Between May 31 and June 6, 2023 there were 119 reverse trajectories have been reported that originated in Kansas and Nebraska and passed over southeastern Saskatchewan and southern Manitoba (Fig. 5).

Figure 5.  The total number of dates with reverse trajectories originating over Kansas and Nebraska that have crossed the prairies between May 1 and June 6, 2023. 

Predicted grasshopper development

Model simulations were used to estimate development of grasshoppers as of June 4, 2023. Compared with average spring temperatures, well above normal temperatures across the prairies continue to result in rapid grasshopper development. Model runs suggest that this spring’s hatch is still proceeding with 68% of the hatch now complete (Fig. 1). In an average year, only 6% of the grasshopper hatch would be completed by this time in June. Hatch is predicted to be well underway across Alberta, western regions of Saskatchewan and southern Manitoba (Fig. 1).

Figure 1. Predicted grasshopper (Melanoplus sanguinipes) hatch (%) across the Canadian prairies as of June 4, 2023. 

As of June 4, 32% of the grasshopper population is predicted to be in the egg stage, 34% first instar, 21% second instar, 12% third instar and 0.5% in the fourth instar. Based on average instar, development is most advanced across Alberta and a large area of Saskatchewan (Fig. 2). Field observations from June 7, 2023 agree with the model predictions.

Figure 2. Predicted grasshopper (Melanoplus sanguinipes) development, presented as average instar, across the Canadian prairies as of June 4, 2023. 

In contrast to 2023, in an average year, most of the grasshopper population would still be in the egg stage or in the first instar stage at this time in early June.

Geospatial maps and model predictions are tools to help time in-field scouting on a regional scale but grasshopper development can vary and is only accurately assessed through scouting. Monitor roadsides and field margins to assess the development and densities of local grasshopper populations. Due to their small size, it may be difficult to visually observe first and second instar grasshoppers in roadside vegetation and field margins. If possible, use a sweep net to sample grasshoppers in ditches and along the edges of crops. Sweep net sampling allows for easier assessments of grasshopper densities at this time of year. Using the grasshoppers collected in sweep nets, we can also determine which life stages are present (which nymphal instars) and the species that are present. Information about grasshoppers and monitoring is available from the Prairie Pest Monitoring Network, in the Field Crop and Forage Pests guide, Alberta Agriculture and Irrigation, Saskatchewan Ministry of Agriculture, and Manitoba Agriculture.

Predicted diamondback moth development

Diamondback moths (Plutella xylostella) are a migratory invasive species; after initial migration into the prairies, diamondback moths can have multiple non-migratory generations during the growing season. Diamondback moth development can be rapid during periods of warm weather. Model simulationsto June 4, 2023, indicate that the first generation of non-migrant adults (based on early-May arrival dates) is currently occurring across the Canadian prairies. If above-normal temperatures persist, then we may start to see some second-generation diamondback moths next week.

The life cycle of diamondback moth can rapidly progress from egg (A) to larvae (B and C), to pupae (D) to adults (E). Photo credit: Jonathon Williams, AAFC-Saskatoon.

On the prairies, we use a network of pheromone traps to detect the first spring appearance of diamondback moths. Now, local scouting is needed to determine if diamondback moth pose a threat to crops. To scout, estimate the number of diamondback moth larvae per m2 at several locations in a field. The economic threshold for diamondback moth is NOT based on pheromone traps or sweep net samples, but on the density of larvae per plant. For immature and flowering canola, the economic threshold is 100-150 larvae/m2. In podded canola, the economic threshold is 200-300 larvae/m2. See the Field Crop and Forage Pests guide and monitoring protocol for more information about scouting for diamondback moth.

Predicted bertha armyworm development

Based on model simulations, development of overwintered bertha armyworm (Mamestra configurata) pupae continues to be significantly ahead of normal for most of the prairies. Bertha armyworm pupae across the prairie region are expected to be at least 90% finished their larval development (Fig. 1); as a result, adults might already be emerging in some areas.

Figure 1. Predicted bertha armyworm (Mamestra configurata) pupal development (%) across the Canadian prairies as of June 4, 2023. 

The bertha armyworm model predicts that adults could already be present in a region between Lethbridge, Alberta and Swift Current, Saskatchewan (Fig. 2). Adult moths may also be flying near Edmonton, Alberta and in the northern limits of the Peace River region (Fig. 2).

Figure 2. The proportion of the bertha armyworm (Mamestra configurata) population that is predicted to be in the adult stage (% of total population) across the Canadian prairies as of June 4, 2023. 

Predicted wheat midge development

Wheat midge (Sitodiplosis mosellana) overwinter as larval cocoons in the soil. Adequate rainfall in May and June is a signal to larval cocoons to end their diapause and move to the soil surface to pupate. where pupation occurs. Insufficient rainfall in May and June can result in delayed movement of larvae to the soil surface. Wheat midge emergence may be delayed or erratic if rainfall does not exceed 20-30 mm during May. The Olfert et al. (2020) model indicated that dry conditions may result in: 
a. Delayed adult emergence and oviposition 
b. Reduced numbers of adults and eggs

Figure 1. Areas in western Canada where cumulative rainfall (mm) from May 1 to June 4, 2023 is sufficient (greater than 30 mm) to promote movement of wheat midge (Sitodiplosis mosellana) larvae to the soil surface. 

In the last few weeks, rainfall events over parts of the prairies may have provided the cue to end wheat midge larval diapause. From May 1 to June 4, cumulative rainfall was normal or above normal in the Peace River region and parts of Saskatchewan (Fig. 1). Larvae, if present, are likely moving towards the soil surface in the Peace River region and in wet areas of Saskatchewan (Fig. 2).  

Figure 2. The proportion of the wheat midge (Sitodiplosis mosellana) larval population that has moved to the soil surface across western Canada, as of June 4, 2023.

In contrast to the wet areas on the prairies, wheat midge adult emergence might be delayed in dry areas 2023. It is also possible that the wheat midge larval cocoons will remain in a diapause state until a future year when spring moisture is more suitable for wheat midge development.

Scouting for adult wheat midge usually starts in late June or early July. Over the next few weeks, the Prairie Pest Monitoring Network will continue to use phenology models to predict that status of wheat midge development and provide additional updates.

For information about scouting, check out the wheat midge monitoring protocol. More information is available from Alberta Agriculture and Irrigation, the Saskatchewan Ministry of Agriculture, and Field Crop and Forage Pests and their Natural Enemies in Western Canada available for free download from our Field Guides page.

Prairie Research

The 2023 growing season is in full swing and researchers working with insects, weeds, plant pathogens, and crops are very busy across the prairie region! For something new this year, the Prairie Pest Monitoring Network will occasionally include Prairie Research Updates in the Weekly Update. This post will highlight the hard work of our colleagues at Agriculture and Agri-Food Canada (AAFC) research centers, at universities, and by other research organizations across western Canada. If you have ideas for a Prairie Research Update, please contact Dr. Meghan Vankosky (meghan.vankosky@agr.gc.ca).

Science News from the Prairies is an AAFC newsletter that highlights work by scientists at AAFC research centres in Alberta, Saskatchewan, and Manitoba. The June 3, 2023 edition highlights the Plant Gene Resources of Canada, a plant gene bank at the AAFC Saskatoon Research and Development Centre. Plant gene banks serve to maintain the genetic diversity of plants by collecting, preserving, and rejuvenating plant reproductive material and sharing their resources to support plant breeding programs, education, and research. Read more about the Plant Gene Resources of Canada and other AAFC research projects in Science News from the Prairies.

To learn more about entomology research at the AAFC Saskatoon Research and Development Centre, please read “Pest Detective: How AAFC is using pest monitoring data to model climate change impacts” available in English and in French.

Provincial Insect Updates

Visit the Alberta Insect Pest Monitoring Network and Crop Insects pages for information about insects and monitoring in Alberta, including links for live maps from the 2023 monitoring season for diamondback moth, bertha armyworm, cutworms and others.

Watch for new issues of the Saskatchewan Crop Production News coming soon in 2023 and browse the articles from 2022 for information from the past.

The latest Manitoba Crop Pest Update for 2023 was posted on June 7. Watch their website for new Crop Pest Updates as the season continues and check out the archives to read past Updates.


Pea leaf weevils may be prowling legume crops, but ground beetles and rove beetles are on the hunt as well. This Insect of the Week features two large groups of insects: ground beetles (Carabid beetles) and rove beetles (Staphylinid beetles). Many of species of ground beetles and some rove beetles are generalist predators, like ants, centipedes and spiders. These arthropods are not picky when it comes to choosing a meal and they often target pests in crop fields. 

From left to right, a Carabid beetle (about 2 cm long), a Carrion beetle (about 2 cm long) and a Staphylinid beetle (less than 1 cm long). Photo credit: Jonathon Williams, AAFC-Saskatoon.

Based on research conducted in western Canada, at least two species of ground beetle have pea leaf weevil on the menu. First, a small beetle called Bembidion quadrimaculatum can feast on pea leaf weevil eggs.

Small bodied (2-3 mm long) Bembidion quadrimaculatum ground beetles can eat pea leaf weevil eggs. Photo credit: Shelby Dufton, AAFC-Beaverlodge Research Farm

A larger beetle called Pterostichus melanarius will catch and eat adult pea leaf weevils. Other pests that different ground beetle species may eat include cutworms, aphids, wheat midge, cabbage root maggots, slugs, and many others! 

A pinned Pterostichus melanarius specimen. These ground beetles eat larger prey, including adult pea leaf weevils. Photo credit: Shelby Dufton, AAFC-Beaverlodge Research Farm
A ground beetle (likely from the genus Pterostichus) next to a finger for scale. Photo credit: A. Harpe, AAFC-Beaverlodge Research Farm

Ground beetles are characterized by long threadlike antennae, have a body that is flattened top-to-bottom, and have strong legs designed for running, large eyes, and obvious jaws (mandibles).  

Rove beetles, like ground beetles, can be important predators of a number of insect pests! Some species will feed on pea leaf weevil eggs. One species of the rove beetle, Aleochara bilineata, is an important natural enemy of cabbage, seedcorn, onion and turnip maggots. Rove beetles are small, thin and have shortened fore-wings that leave most of their abdomen exposed.  

A pinned Staphylinid (rove) beetle (<1cm long). Photo credit: Shelby Dufton, AAFC-Beaverlodge Research Farm

For more information on these field heroes and the other pests they help to manage, see the Field Crop and Forage Pests and their Natural Enemies in Western Canada guide. The guide has helpful information about the life cycle of these and other predators. The guide also has tips for conserving predators and parasitoids and pictures to help with identification. Please visit the PPMN Field Guide page to download a copy of the guide in French.