The first adult wheat midge of 2023 were reported in Saskatchewan last week. This year could be an interesting year for wheat midge. Some areas have had sufficient rain to trigger the end of diapause and the completion of larval and pupal development. If adult emergence coincides with susceptible crop stages, damage could result. Scouting for wheat midge right now is very important!
This is a busy week for our field research programs across western Canada. In particular, the annual cabbage seedpod weevil survey has begun. 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.
Because we are so busy in the field, this Weekly Update is shorter than usual. We decided to focus on wheat midge due to adult emergence reported last week, but do not forget about grasshoppers, diamondback moths, or bertha armyworm. This Weekly Update includes a short post with important links for all three of these species.
This week, the Insect of the Week also featured the wheat midge, a pest of cereal crops. In the next two weeks, we will feature the parasitoid of cereal leaf beetle and 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.
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.
During the week of June 19-25, the prairie average daily temperature was 1°C warmer than normal (Fig. 1). The warmest temperatures were observed across Manitoba, with Dauphin, Manitoba recording temperatures 4.5°C warmer than normal. The coolest temperatures occurred across eastern Alberta. Calgary, Alberta, for example was 2°C cooler than normal.
Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for the period of June 19-25, 2023.
Average temperatures over the past 30 days (May 27 to June 25, 2023) have been 3.5°C above normal with the warmest values being reported across Manitoba and Saskatchewan (Fig. 2). Relative to climate normals, Dauphin, Manitoba was 5.5°C warmer than normal. In the last 30 days, temperatures have been coolest in the Peace River region; Grande Prairie, Alberta was only 1°C warmer than normal.
Figure 2. 30-day average temperature (°C) across the Canadian prairies for the period of May 27 to June 25, 2023.
Seven-day cumulative rainfall was greatest in a region around Edmonton, Alberta (Fig. 3). Precipitation amounts were minimal for southern Alberta and a large area of Saskatchewan.
Figure 3. Seven-day cumulative rainfall (mm) observed across the Canadian prairies for the period of June 19 – 25, 2023.
The greatest 30 day rainfall totals (100-160mm) were reported from a region near Edmonton, Alberta (Fig. 4); rainfall totals in some of those areas have been 200% of normal. Rainfall amounts continue to be low across the southern prairies and near Saskatoon, Saskatchewan. For example, at Carman, Manitoba rainfall has been only 26% of normal and Brooks, Alberta has received only 49% of the precipitation expected in an average year.
Figure 4. 30-day cumulative rainfall (mm) observed across the Canadian prairies for the period of May 27 to June 25, 2023.
Wheat midge (Sitodiplosis mosellana) development is ahead of normal. 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 life-stage (Fig. 1). Recent rainfall in the Peace River region and Edmonton regions may have resulted movement of larvae to the soil surface and subsequent occurrence of pupae. First emergence of adults was reported last week.
Figure 1. Percent of wheat midge (Sitodiplosis mosellana) that is predicted to be in the pupal stage in western Canada, as of June 25, 2023.
Model simulations indicate that adults may be occurring in fields near Saskatoon, Regina, Estevan and Melita (Fig. 2). It is expected that adult populations may peak later next week. Oviposition is predicted to begin over the next few days.
Figure 2. Percent of wheat midge (Sitodiplosis mosellana) that is predicted to be in the adult stage in western Canada, as of June 25, 2023.
Based on the occurrence of wheat midge adults, field monitoring should begin now. In order to assess wheat midge populations and to take the appropriate action, 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.
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 south, densities are quite high and crop damage is being reported, as well as spraying to protect crops.
Model simulations for grasshopper development indicate that grasshoppers should range from first to fifth instars with some adults now present at many locations across the prairies, as of June 25. Based on average instar, development is most advanced across the southern prairies where 65% of the population is predicted to be fourth and 5th instar, with some adults also present (Fig. 1). In an ‘average year’, the majority of the grasshopper population (60%) would typically be in the first, second, and third instars in late June.
Figure 1. Predicted grasshopper (Melanoplus sanguinipes) development, presented as average instar, across the Canadian prairies as of June 25, 2023.
Based on occurrence of fifth instar grasshoppers, development is most advanced across southern Manitoba (Fig. 2).
Figure 2. Predicted migratory grasshopper (Melanoplus sanguinipes) development, presented as the percent of the population in the fifth instar, across the Canadian prairies as of June 25, 2023.
Adult two-striped grasshoppers (Melanoplus bivittatus) and migratory grasshoppers (M. sanguinipes) have been observed across the southern prairies.
Last week, models predicted that first instar bertha armyworm larvae might be present in some areas of the prairies. Bertha armyworm larvae could also be developing quickly, thanks to warm weather. The network of pheromone traps across the prairies is reporting low numbers of adults (less than 300 cumulative catch), including in Manitoba (check out the June 21 Manitoba Crop Pest Update) and Alberta. Risk to yield from bertha armyworm increases when cumulative trap catches exceed 300 (300-900 = medium risk, >900 = high risk). For information about scouting, check out the PPMN protocol and the Alberta Agriculture and Irrigation pages.
Diamondback moth
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 Rosetown and Swift Current in Saskatchewan, in the Vulcan area in Alberta, and in the Central, Eastern, and Interlake regions in Manitoba (see the June 21 Manitoba Crop Pest Update). Like grasshoppers and bertha armyworm, diamond back moth development occurs quickly in warm weather. Last week, we predicted that diamondback moths had reached the second non-migrant generation and we heard of some sightings of larvae in some areas of the prairies. Because diamondback moth can have multiple generations in a single growing season, 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.
Developing tools for the management of Lygus bugs in faba bean
*The text of this post was written by Teresa Aguiar-Cordero and Sean Prager.
This research project, led by Sean Prager and Teresa Aguiar-Cordero, focuses on studying insects in the genus Lygus and their impact on faba bean crops in the province of Saskatchewan. Faba beans are a significant legume crop in the region, but they face threats from various insect pests, including Lygus species. Lygus bugs feed on faba beans by injecting salivary enzymes into the plant, resulting in damage such as hull perforations, seed coat discoloration, and tissue wilting which reduces yield. Damage to seed lowers the quality and grade of faba beans below that for human consumption with substantial economic consequences.
Microscope image of an adult Lygus bug. Picture provided by Teresa Aguiar-Cordero, University of Saskatchewan.
The project aims to address crucial knowledge gaps regarding Lygus bugs in faba beans. By conducting a survey across Saskatchewan, the study aims to determine the optimal timing and methods for effective Lygus sampling. In addition to the survey, a series of no-choice bioassay are currently being performed to quantify the relationship between Lygus bug numbers and the resulting damage to faba bean pods, which can help develop action thresholds.
Faba bean pods with damage resulting from Lygus bug feeding activity. Picture provided by Teresa Aguiar-Cordero, University of Saskatchewan.
As part of the future directions, the researchers plan to incorporate the electrical penetration graph technique (EPG) to gain a better understanding of the feeding behavior of Lygus bugs in faba beans. This technique will provide valuable insights into the precise feeding patterns employed by Lygus bugs.
In addition, a series of choice bioassays will be conducted to analyze and determine the preferences of Lygus when given a choice of different crop and plant species. This will help establish which crops Lygus may migrate into faba bean from. By studying the preferences of Lygus bugs for different crops, the researchers aim to identify potential trap crops that can attract Lygus populations as part of a management program to reduce the impact of Lygus bugs on faba bean crops.
The project’s outcomes will contribute important information and management tools for growers, enabling them to mitigate the impact of Lygus insects on faba bean crops. By understanding the associations between Lygus numbers and damage, and exploring innovative strategies such as trap crops, the project strives to minimize damage and decrease losses for growers.
Teresa Aguiar-Cordero is a graduate student at the University of Saskatchewan, working with Dr. Sean Prager to study Lygus bugs.
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 (new last week!).
New issues of the Saskatchewan Crop Production News are coming soon in 2023. Use the link to browse the articles from 2022 or subscribe to receive new issues of the newsletter as they are published online.
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).
Now is the time to get out and scout for wheat midge!
Wheat midge are small, orange, fragile-looking flies that attack members of the grass family including barley, couch grass, wheat grass, triticale, and spring rye, though their preferred host is wheat.
Adult wheat midge. Picture credit: Shelby Dufton and Amanda Jorgensen, both of AAFC-Beaverlodge.
Adults emerge from mid-June through mid-July and typically coincide with wheat head development and flowering. Wheat midge remain in the humid crop canopy throughout the day and emerge on calm, warm evenings to mate and lay eggs. Eggs are laid singly or in groups of three to five on wheat kernels prior to flowering.
Adult wheat midge. Picture credit: Shelby Dufton and Amanda Jorgensen, both of AAFC-Beaverlodge.
Upon hatching, larvae crawl to developing kernels and feed for two to three weeks. Larval feeding damage results in shriveled, misshapen, cracked, or distorted kernels. Kernels must be inspected within the glume, as damage may not be readily apparent at a glance. Lost or damaged kernels from feeding result in lower crop yield and quality. The Canadian Grain Commission allows midge damage between two and five percent prior to impacting the assigned grade.
Wheat midge larva on a damaged wheat kernel. Picture credit: Amanda Jorgensen, AAFC-Beaverlodge.
After feeding, larvae remain inside the heads until rain or a moisture event occurs, at which point they drop to the soil, bury themselves, and form a cocoon to overwinter. In the spring, if moisture and temperature requirements are met, larvae leave their cocoons and return to the soil surface, pupating for a period of two weeks.
Wheat fields should be inspected for wheat midge in late June and early July, as wheat heads emerge, and females are laying eggs on the developing heads. Scouting should occur in the evening (after 8:30 PM) on calm, warm (15 ˚C) evenings. The number of adults should be counted on four to five wheat heads in three or four locations. Insecticide applications should be considered if economic thresholds are met. To maintain optimum grain grade, the economic threshold is one adult wheat midge per eight to ten heads during susceptible stages (wheat head emergence up until flowering). To prevent yield loss, the economic threshold is one adult wheat midge per four to five heads.
Varieties of midge tolerant wheat are available to help manage this pest! More information on these can be found at www.midgetolerantwheat.ca.
Are there any natural enemies that stand up to wheat midge? Yes! The parasitoids will be featured in an upcoming issue of Insect of the Week.
