2023 WEEK 9 (Released July 7, 2023)

Meghan Vankosky
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Week 9

Insect scouting season is in full swing after the long weekend! The Prairie Pest Monitoring Network is busy with the annual cabbage seedpod weevil survey right now. Grasshoppers, wheat midge, and moths remain on our radar though, with development of many insect pests ahead of schedule this year thanks to warmer than average weather.

The first adult wheat midge of 2023 were reported in Saskatchewan in late June. Although not all areas had enough rainfall at the right time for wheat midge development, but scouting for wheat midge will be important in wetter areas. Models suggest that pupal development is well underway and that adults are flying and laying eggs in some areas. This could be an interesting year for wheat midge.

Adult grasshoppers are becoming more common across the prairies now. Diamondback moth could be entering into the third non-migrant generation in some areas (if present), and the peak flight of adult bertha armyworm should now be finished. Where present, bertha armyworm populations should mostly consist of larvae. Use information from this Weekly Update and updates from our provincial partners to learn more about risk in your area and to plan scouting activities.

This is a busy time for our field research programs across western Canada. In particular, the annual cabbage seedpod weevil survey is well underway. For farmers in Alberta, watch the map for near-real-time monitoring results from the cabbage seedpod weevil survey! It looks like some fields in southern Alberta have high numbers of cabbage seedpod weevils. The PPMN monitoring protocol for cabbage seedpod weevil is available on the Monitoring Protocol page.

This week, the Insect of the Week featured Tetrastichus julis, a parasitoid that attacks cereal leaf beetle. Next week, look for our post about natural enemies of wheat midge.

Remember, insect Monitoring Protocols containing information about in-field scouting as well as information about insect pest biology and identification.

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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.

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Weather Synopsis

Ross Weiss, Tamara Rounce, Jennifer Otani and Meghan Vankosky
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Week 9

During the week of June 26 – July 2, 2023, the average daily temperature was 3°C warmer than normal on the prairies. The weekly average temperature in Dawson Creek, British Columbia was 17.8 °C, a whopping 5°C warmer than normal. The warmest temperatures were observed across the southern prairies last week (Fig. 1). The weekly average temperature at Carman, Manitoba was 22°C (4.4°C warmer than normal). The coolest temperatures occurred across northwestern Alberta.

Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for the period of June 26 to July 2, 2023. 

Average temperatures over the past 30 days (June 3 – July 2, 2023) have been 3°C above normal with the warmest values reported across Manitoba and eastern Saskatchewan (Fig. 2). Relative to climate normals, many Manitoba locations have been 4°C  warmer than normal over the last 30 days of 2023. Though warmer than normal, temperatures continue to be coolest in the Peace River and Edmonton regions.

Figure 2. 30-day average temperature (°C) across the Canadian prairies for the period of June 3 to July 2, 2023. 

Since April 1, warmest temperatures have been reported across the southern prairies (Fig. 3). The coolest temperatures have been observed across eastern Saskatchewan.

Figure 3. Growing season average temperature (°C) observed across the Canadian prairies for the period of April 1 to July 2, 2023.  

Between June 26 and July 3, 2023 only small amounts of rainfall were recorded across most of Alberta and Saskatchewan. The exception was the Parkland region of both provinces, where more than 15 mm of rain was recorded (Fig. 4). Seven-day cumulative rainfall was greatest in Manitoba, where many locations reported rain amounts greater than 20 mm.

Figure 4. Seven-day cumulative rainfall (mm) observed across the Canadian prairies for the period of June 26 to July 2, 2023. 

The greatest 30 day (June 3 – July 2, 2023) rainfall totals (100-160mm) were reported from a region near Edmonton, Alberta where rainfall totals are 200% of normal (Fig. 5). Rainfall amounts continue to be low across the southern prairies, particularly southern Alberta.

Figure 5. 30-day cumulative rainfall (mm) observed across the Canadian prairies for the period of June 3 to July 2, 2023. 

Since April 1, prairie rainfall has generally been below normal (Fig. 6). The driest region is southern Alberta where rainfall received so far in 2023 is only 40% of the average rainfall for the region. A region extending from Oyen to Taber has had less than 60 mm rain in 2023 (Fig. 6). Over the same time period, this region has also been one of the warmest regions of the prairies (Figs. 3). 

Figure 6. Growing season cumulative rainfall (mm) observed across the Canadian prairies for the period of April 1 to July 2, 2023.  
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Predicted Wheat Midge Development

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 9

Wheat midge (Sitodiplosis mosellana) development is ahead of normal in 2023. Last week, wheat midge pupae were just beginning to appear at the soil surface. This week, where wheat midge populations are present, pupae should be the most abundant lifestage (Fig. 1).

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

First emergence of adults was reported last week and the model indicates that peak emergence has not yet occurred. Model simulations indicate that eggs and larvae should be occurring in fields across Saskatchewan and western Manitoba (Fig. 2). 

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

Based on the occurrence of wheat midge adults, field monitoring should begin now, if it has not started already. In order to assess wheat midge populations and to take the appropriate action for management, it is recommended that fields should be monitored when wheat is between heading and flowering. Field inspection should be carried out after 8:30 p.m. when the female midge are most active. Females are more active when the temperature is above 15°C and wind speed is less than 10 km/h. Wheat midge populations can be estimated by counting the number of adults present on four or five wheat heads. 

For more information about scouting and economic thresholds, 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.

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Grasshoppers

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 9

Development of the pest grasshoppers continues to be ahead of schedule in 2023, as compared to past years. The first adult two-striped grasshoppers (Melonplus bivittatus) were collected on June 15 (Alberta) and June 19-20 (Saskatchewan). No one that we’ve spoken to remembers finding adult two-striped grasshoppers in June before. Especially in the southern prairies, densities are quite high and crop damage is being reported, as well as spraying to protect crops.

Model simulations were used to estimate development of grasshoppers as of July 2, 2023 and indicate that about 75% of the prairie grasshopper population should be in the 4th or 5th instar (Fig. 1). In an average year, we would expect 52% of the prairie grasshopper population to be in the 2nd or 3rd instar in early July (Fig. 2).

Figure 1. Predicted grasshopper (Melanoplus sanguinipes) development, presented as average instar, across the Canadian prairies as of July 2, 2023. 
Figure 2. In an average year (based on 30-year average weather or climate normals), about 50% of the grasshopper population would be expected to be in the second or third instar in early July as pictured here on the map. In contrast, in 2023, warm weather has significantly sped up the rate of grasshopper development.

Reports of adult occurrence suggest that adults are occurring much earlier than normal. The grasshopper model, developed for pest grasshoppers, indicates that adult grasshoppers should now be occurring across most of the southern prairies (Fig. 3).  

Figure 3. Predicted migratory grasshopper (Melanoplus sanguinipes) development, presented as the percent of the population that now in the adult stage, across the Canadian prairies as of July 2, 2023. 

Geospatial maps are a tool to help time in-field scouting on a regional scale but grasshopper development can vary and is only accurately assessed through scouting. In Saskatchewan, grasshoppers have be observed in field crops. Monitor roadsides and field margins to assess the development and densities of local grasshopper populations.  

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 Irrigation, Saskatchewan Ministry of Agriculture, and Manitoba Agriculture. 

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Diamondback Moth

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 9

Diamondback moths are a migratory invasive species; in 2023, the first migratory adults were found in pheromone traps in early May. Thanks to the above average warm weather across most of the prairie region this year, diamondback moth development is well ahead of average. Based on development models and weather to July 2, a third generation of non-migrant adults is expected to be occurring in some parts of the prairies (Fig. 1), with the second generation occurring in nearly all other areas of the 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 2, 2023.  

Diamondback moth typically have 4 full generations during prairie summers. In an average year, we would expect that the second generation of non-migrant diamondback moth would we widespread right now, NOT the third non-migrant generation (Fig. 2).

Figure 2. Number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the prairie region by early July in a ‘normal’ year (based on 30-year average or long-term normal weather data).

Some areas of the prairies might be at risk of damage from diamondback moth. Pheromone traps with cumulative counts greater than 25 male moths so far in 2023 are located around Cadillac, Rosetown, Makwa, Eatonia, and Swift Current in Saskatchewan, in the Vulcan area in Alberta, and in all regions of Manitoba (see the July 5 Manitoba Crop Pest Update). In Manitoba, the highest counts of diamondback moths in pheromone traps exceed 200 total moths in the Central and Eastern regions. 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 later 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.

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Bertha Armyworm

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 9

Based on model simulations, bertha armyworm development continues to be 7-10 days ahead of normal. Where present, populations of bertha armyworm will largely be in the larval stage (Fig. 1).

Figure 1. The proportion (%) of the bertha armyworm (Mamestra configurata) population that is expected to be in the larval stage across the Canadian prairies as of July 2, 2023. Note that bertha armyworm may not be present at all locations.

The larvae of this generalist moth could be found in canola fields, but also in other crops.

The lifestages of bertha armyworm: A) eggs, B) larva, C) pupa, and D) adult. All pictures taken by Jonathon Williams, AAFC-Saskatoon (please include a photo credit if these pictures are reproduced elsewhere).

The network of pheromone traps across the prairies is reporting low numbers of adults (less than 300 cumulative catch over the last 6 weeks) so far in 2023, including in Manitoba (check out the July 5 Manitoba Crop Pest Update), Saskatchewan, and Alberta. Only one monitoring location (in Manitoba) has caught more than 300 bertha armyworm adults so far this year, suggesting relatively low risk across the prairies. Risk to yield from bertha armyworm increases when cumulative trap catches exceed 300 (300-900 = medium risk, >900 = high risk). Although the pheromone trap network suggests low risk of economic damage from bertha armyworm, it is still important to scout for larvae. For information about scouting, check out the PPMN protocol and the Alberta Agriculture and Irrigation pages.

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Provincial Insect Updates

John Gavloski, Shelley Barkley, James Tansey and Meghan Vankosky
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Week 9

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.

The first Saskatchewan Crop Production News issue is now online! Use the link to read Issue #1 and watch for future issues. Issue #1 for 2023 includes information about springtails and wheat midge. 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).

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TETRASTICHUS JULIS

Amanda Jorgensen, Shelby Dufton, Jennifer Otani and Meghan Vankosky
Categories
Week 9

The cereal leaf beetle larvae you see in wheat fields may be full of this week’s Insect of the Week, Tetrastichus julis. This parasitoid wasp is an important natural enemy of cereal leaf beetle. Adult T. julis lay their eggs inside cereal leaf beetle larvae, leaving about five eggs to consume the beetle from the inside out. Adult parasitoids feed on nectar and aphid honeydew.  

A Tetrastichus julis female in the process of parasitizing a cereal leaf beetle larva, sitting on a wheat leaf with cereal leaf beetle feeding damage. Picture credit: Emily Lemke and Karen Shamash, AAFC-Lethbridge.

Mature T. julis larvae overwinter in infested cereal leaf beetle cocoons and emerge in spring to lay more eggs in cereal leaf beetle larvae. Where T. julis has become established, it can reduce cereal leaf beetle populations by 40 – 90%, preventing yield loss without using pesticides. See also the factsheet, Biological Control at its Best, Using the T. julis Wasp to Control the Cereal Leaf Beetle (en français).  

AAFC researchers have assisted T. julis in establishing and spreading to help control cereal leaf beetle populations in the Canadian prairies! Reducing the use of insecticides (if possible), leaving refuge areas, and reducing tillage can all help protect populations of this valuable parasitoid in areas where they are already established in a field.  

Biological information related to T. julis and cereal leaf beetle in field crops is available online. For more information, visit the cereal leaf beetle 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).  

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