2023 Week 11 (Released July 20, 2023)

Insect scouting season continues! Development of many pest insects (and of their host crops) is ahead of schedule this year, thanks to warmer than average weather during this growing season.

Adult grasshoppers are becoming more and more common across the prairies. Although grasshoppers are more widespread this year than in the past few years, the stage of grasshopper development and grasshopper population densities can vary between even relatively close locations. Scouting individual fields is important to best estimate crop risk.

Diamondback moth, if present, are into the third non-migrant generation across most of the prairies. Keep in mind that diamondback moth develop quickly in warm weather which could lead to rapidly increasing populations over the summer. Scout when you can and use the links in the Provincial Insect Updates post to learn about diamondback moth and bertha armyworm risk in your region. Diamondback moth was also the Week 11 Insect of the Week!

There is now a monitoring protocol for canola flower midge! As canola flowering finishes, it can be easy to see the galled flowers that result from infestation by canola flower midge, so the time to scout could be now. A three-year survey completed in 2019 found that canola flower midge is quite widely distributed across the prairies, but in relatively low densities and probably doesn’t cause economic yield losses. If you scout for canola flower midge this year and are willing to share your results please send them to meghan.vankosky@agr.gc.ca. If we get enough information, we will map the results!

This is a busy time for our field research programs across western Canada and with upcoming field days, we are even busier. A list of events can be found on the Prairie Pest Monitoring Network homepage and in the Week 10 update

Watch out for Invasive and Migrating Insects! The Insect Surveillance Community Practice has created posters for the Prairie Region, BC, Ontario & Quebec, and Atlantic Canada to raise awareness of potentially invasive insects to each region. If you suspect that you have found any of the insects on the Prairie Region Poster, please let us know using the form linked to the QR code on the poster. Note: many of us entomologists on the prairies are members of the Insect Surveillance Community of Practice!

Remember: insect Monitoring Protocols containing information about in-field scouting as well as information about insect pest biology and identification are available from the Prairie Pest Monitoring Network.

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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

The average daily temperature across the prairies was 0.5°C cooler than climate normals during the week of July 10 to July 16, 2023. However, specific locations remained warmer than normal, including Fort St. Jean, British Columbia, where it was 4°C warmer than normal; the warmest weekly average temperatures occurred across most of the Peace River region, southern Alberta, and southwestern Saskatchewan (Fig. 1). The coolest temperatures occurred across eastern Saskatchewan and western Manitoba with many locations having weekly average temperatures that were 2-4°C cooler than average.

Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for the period of July 10-16, 2023. 

Average temperatures over the past 30 days (June 17 – July 16, 2023) have been almost 1°C above normal; many locations in the Peace River region have reported 30 day average temperatures that were 3°C warmer than average. The warmest 30-day temperatures were reported across most of the southern prairies, particularly southern Manitoba (Fig. 2).

Figure 2. 30-day average temperature (°C) across the Canadian prairies for the period of June 17 to July 16, 2023. 

Precipitation during the week of July 10 to July 16, 2023 was minimal across most of the prairies (Fig. 3). Precipitation amounts ranged from 0.1mm at Lloydminster, Alberta/Saskatchewan to 34mm at Red Deer, Alberta. Average prairie precipitation (44 mm) for June 17-July 16, 2023) is 71% of normal. Unfortunately, much of the rain since July 10 has been accompanied by hail in some areas.

Figure 3. Seven-day cumulative rainfall (mm) observed across the Canadian prairies for the period of July 10-16, 2023. 

Cumulative rainfall for the past 30 days was greatest in the Edmonton region; the lowest rainfall amounts continue to be observed across most of Saskatchewan and southern Alberta (Fig. 4). Rain totals in the last 30 days ranged considerably from location to location. Mayerthorpe, Alberta had 131 mm in the last 30 days (167% of normal). In contrast, Taber, Alberta had only 6mm of rain (16% of normal) in the same period.

Figure 4. 30-day cumulative rainfall (mm) observed across the Canadian prairies for the period of June 17 -July 16, 2023. 

Since April 1, conditions across the prairies have generally been quite dry. Precipitation accumulation has been below normal across most of Saskatchewan and southern Alberta (Fig. 5). Most of the prairie region has had less than 88% of normal or expected precipitation so far in 2023. However, some areas have received more rainfall than normal, especially locations around Edmonton, Alberta.

Figure 5. Growing season cumulative rainfall, expressed as the percent of normal/expected rainfall, observed across the Canadian prairies for the period of April 1 to July 16, 2023. 

Predicted Grasshopper Development

Based on earlier than normal appearance of adults, high densities and drought conditions, grasshopper risk continues to increase and may be significant for large areas of Alberta, Saskatchewan, and southern Manitoba. Model simulations were used to estimate development of grasshoppers as of July 16, 2023. As a result of warmer than normal temperatures, grasshopper development continues to be well ahead of average. Simulations indicate that 51% of the prairie population should now be in the adult stage (Fig. 1).

Figure 1. Predicted migratory grasshopper (Melanoplus sanguinipes) development, presented as the percentage of the population in the adult stage, across the Canadian prairies as of July 16, 2023. 

In contrast, in a ‘normal’ year we would expect that 60% of the population would be in the fourth or fifth instar, with less than 5% of the population in the adult stage in mid-July (Fig. 2).

Figure 2. Predicted migratory grasshopper (Melanoplus sanguinipes) development, presented as the percentage of the population in the adult stage, across the Canadian prairies as of July 16 in a ‘normal’ year, based on long-term average weather data. 

Geospatial maps are a tool to help time in-field scouting on a regional scale but grasshopper development and population densities can vary over relatively small distances. Scouting is required to accurately assess the stage of grasshopper development and estimate their densities.

Information about grasshoppers and grasshopper monitoring is available from the Prairie Pest Monitoring Network, in the Field Crop and Forage Pests guide, Alberta Agriculture and IrrigationSaskatchewan Ministry of Agriculture, and Manitoba Agriculture

Predicted Wheat Midge Development

Wheat midge (Sitodiplosis mosellana) emergence is reduced when soil moisture is insufficient to terminate spring diapause. Dry conditions in southcentral Manitoba as well as central and southern regions of Alberta have likely resulted in reduced emergence of larvae from the soil.

In regions where rainfall was sufficient to trigger the end of wheat midge diapause and the completeion of wheat midge development, we expect that eggs and larvae should be the most abundant life stages (Figs. 1 and 2).

Figure 1. Proportion (%) of the wheat midge (Sitodiplosis mosellana) population that is predicted to be in the egg stage in western Canada, as of July 16, 2023. 
Figure 2. Proportion (%) of the wheat midge (Sitodiplosis mosellana) population that is predicted to be in the larval stage in western Canada, as of July 16, 2023. 

Simulated development at Regina, Saskatchewan and Grande Prairie, Alberta indicates that adult emergence has peaked (Fig. 3). Development in the Peace River region is approximately 1 week behind development of wheat midge in eastern Saskatchewan. 

Figure 3. Predicted development of wheat midge (Sitodiplosis mosellana) near Regina, Saskatchewan and in the Peace River region as of July 16, 2023. Note, Sm L1-2 in the legend refers to wheat midge larvae that are feeding in wheat heads. The model used to simulate wheat midge development was developed by Olfert et al. (figure by Ross Weiss, 2023).

It may still be important to be scouting for adult wheat midge in some areas of the prairies. For more information about scouting and economic thresholds for wheat midge, check out the wheat midge monitoring protocol and the Insect of the Week for Week 8, that featured wheat midge. 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.

Predicted Diamondback Moth Development

In summer 2023, diamondback moth development is well ahead of average. Model simulations to July 16, 2023, indicate that the third generation of non-migrant adults (based on early May arrival dates) is currently occurring across the Canadian prairies (Fig. 1).

Figure 1. Predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of July 16, 2023.

When we ran the model using long term average weather data (based on climate normals), the model output showed that the second generation of diamondback moth would be occurring at this date in a ‘normal’ year (Fig. 2). Above normal temperatures in 2023 have increased the rate of diamondback moth development, resulting in three generations in the time it usually takes for the development of two generations!

Figure 2. The number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of July 16, based on climate normal data. 

Some areas of the prairies might be at risk of damage from diamondback moth this summer. Pheromone traps with cumulative counts greater than 25 male moths were located around Cadillac, Rosetown, Makwa, Eatonia, and Swift Current in Saskatchewan, in the Vulcan area in Alberta, and in all regions of Manitoba (data in the July 5 Crop Pest Update). According to the July 19 edition of the Manitoba Crop Pest Update, canola fields in the Plum Coulee, St. Joseph and Dominion City areas of Manitoba had high levels of diamondback moth larvae in the last week.  Because diamondback moth can have multiple generations in a single growing season and because the generation time is shorter when temperatures are warm, their populations can build up quickly. Keep scouting for diamondback moth to avoid unpleasant surprises at the end of this summer.

To scout for diamondback moth, 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.

Canola Flower Midge Scouting

Scouting for canola flower midge tends to be easiest as the flowering stage of canola ends and pod development begins. Female canola flower midge lay eggs on developing canola buds and larvae develop inside the buds, resulting in galled flowers that do not open or produce pods.

Although canola flower midge does not appear to occur at densities that cause economic damage, scouting for canola flower midge will help to monitor population growth at the local scale to avoid surprises in the future. The monitoring protocol used during our survey from 2017-2019 is now available online so that everyone can scout for canola flower midge.

Check out the Canola Flower Midge Scouting post from Week 10 for pictures of damage caused by this insect and to see a map of canola flower midge distribution.

Watch Out for Invasive Insects

From the Insect Surveillance Community of Practice:

Do you spend time monitoring, photographing or observing insects? If so, your help is needed to watch for and report invasive and migratory insect pests that harm plants, causing damage to Canada’s environment, farm lands, forests, parks and other natural areas. Early detection is critical for slowing the spread of these insect pests. 

View the poster for your region (links below) to learn more about priority insect pests to watch out for. Use the QR codes on the posters to report your detections!

A sample from the Priority Invasive and Migratory Insects to Report poster for the Prairie Region. Use the links below to view and download the full version of the Prairie Region poster, as well as posters for other regions in Canada.

This initiative is a collaborative project developed by the Insect Surveillance Community of Practice of the Canadian Plant Health Council, a multi-partner body that coordinates action for the protection of plant health in Canada. 

Prairie Region (French version here)

British Columbia (French version here)

Ontario & Quebec (French version here)

Atlantic Canada (French version here)

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 cabbage seedpod weevil.

Saskatchewan Crop Production News issues are now online! Use this link to read Issue #2 and watch for future issues. Issue #2 for 2023 includes information plant diseases and plant staging for pesticide applications. There are links on the Crop Production News page so that interested readers can subscribe to the newsletter.

Weekly Manitoba Crop Pest Updates for 2023 are available online with timely updates about insect pests, weeds, and plant pathogens. Watch their website for new Crop Pest Updates (usually published on Wednesdays this year).


The diamondback moth (Plutella xylostella) is an invasive species that migrates northward to the Canadian Prairies on wind currents from infested regions in the USA. Upon arrival, migrant diamondback moths begin to reproduce, resulting in non-migrant populations that may have three or four generations on the prairies during the growing season. The time required for diamondback moth to complete a generation gets shorter when temperatures are warm. In warmer years, diamondback moth populations can build up relatively quickly, increasing their chances of causing economic damage to crops where populations are present. Host plants of diamondback moth include canola, mustard and other cruciferous vegetables and weeds. 

A diamondback moth pupa inside a cocoon on a canola leaf. Picture credit: Jonathon Williams, AAFC-Saskatoon.

Diamondback moths lay their eggs on leaves. Hatchling larvae emerge and tunnel into the leaves, later moving to the surface to feed. Damage first appears as shot holes but eventually expands until the leaves are skeletonized, leaving only the leaf veins. Larvae also feed on flowers and strip the surface of developing pods and stems. Larval damage lowers seed quality and crop yield of canola and can affect the marketability of crucifer vegetables.

The lifecycle of diamondback moth: A) eggs, B) early instar larva with damage typical of this life stage, C) late instar larva on a skeletonized leaf, D) pupa, and E) adult moth. All pictures taken by Jonathon Williams, AAFC-Saskatoon.

Adult moths measure 12 millimeters long with an 18-20 millimeter wingspan. At rest, their forewings form a diamond-shaped pattern along the mid-line. Mature larvae are 8-millimetre-long green caterpillars. Their terminal prolegs extend backwards, resembling a fork. When disturbed, caterpillars drop towards the ground on a silken thread to avoid harm. 

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 and Alberta). 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).