Wheat midge – Survey and maps

Overview

The 2023 wheat midge survey results showed generally a low population of wheat midge throughout the province with the exception of a few fields in the Camrose-Edmonton region.

The parasitoid of wheat midge Macroglenes penetrans numbers were also low. This is not unexpected as the wheat midge numbers were low in 2022 survey. Keep in mind, wheat midge can remain as a diapausing, cocooned larva in the soil for at least one cropping year; a resurgence of the population can occur if there is a higher than normal rainfall in May and June.

Over the past several years, the field-to-field variation has been considerable throughout the province. Individual fields throughout Alberta may have economic levels of midge. Each producer needs to assess their risk based on indicators specific to their farm. Specifically, producers should pay attention to midge downgrading in their wheat samples and use this as an indication of midge risk in their fields. Even though the map may indicate that there is not a risk for midge in a specific area, that does not mean that there is no risk.

For information on identification, life cycle, damage and pest management, see Wheat midge – Overview.

Methodology

The 2023 growing season in southern Alberta was the 6th driest in weather records going back 99 years.¹ This situation forced us to take a different approach to the 2023 survey.

Wheat midge is dependent on May and June rain and temperature to complete its development from larva to adult. Throughout southern Alberta, no appreciable rainfall occurred in the spring or summer. Weighing the lack of environmental conditions that favour larval development the decision was made to change survey procedures.

Only irrigated fields were sampled in the area from south of Calgary and east to the Saskatchewan-Alberta border. In the municipalities of Acadia and Special Area 2 and 3 sampling for wheat midge was not done.

In total, 253 samples (31 samples from irrigated; 212 from dryland) were taken from 60 counties. The survey involves taking soil samples from wheat fields after harvest using a standard soil probe. Larval cocoons are washed out of the soil using a specialized series of screens. Larvae are counted, and then dissected to determine parasitism levels in the midge. The midge density displayed on the forecast map is based on viable (live, non-parasitized) midge larvae.

Survey findings

Image of a map of Alberta showing the Wheat Midge Forecast

Wheat Midge Survey 2023 (map)

This forecast is not intended to take the place of individual field monitoring populations in individual fields can be and often are highly variable. Producers should plan to monitor their fields when the midge adults are flying and their wheat is in the susceptible stage, from the boot leaf until anthers are visible on the heads. Regular field scouting on multiple nights in succession is important in understanding the population in a particular field.

Keep in mind, even if you are in the green areas of the map, wheat midge could still be an issue if weather conditions favour their development.

Although a number of factors influence the overwintering survival of the midge, the survey and map provide a general picture of existing densities and the potential for infestation in 2024. Weather conditions, specifically temperature and moisture will ultimately determine the extent and timing of midge emergence during the growing season. Temperature and wind also play critical roles in egg laying activities of the adult female wheat midge. The level of damage from wheat midge is determined by the synchrony of wheat midge emergence and wheat and the number of wheat midge present. Look for the results of our wheat midge pheromone trapping in June and July to help track adult midge emergence.

Parasitism of midge larvae by a small wasp species (Macroglens penetrans) has been important in keeping wheat midge populations below the economic threshold in many areas. These beneficial wasps tend to thrive in warm, dry conditions. Parasitoid populations increase and decrease with changes in the midge population and are very important in moderating population levels in Alberta. It is important to understand that once midge has established in an area it unlikely to ever completely disappear. Low-lying and moist areas in fields provide a refuge, enabling the population to survive even when conditions are not favorable in the rest of the field. These low population levels, however, also help sustain a population of natural enemies.

Acknowledgements

The wheat midge survey was conducted by the Agriculture and Irrigation, Plant and Bee Health Surveillance Section with assistance from:

Mountain View County
Parkland County

Thank you for your contribution.

Thank you Adriana Van Tryp for your dedication to the field sampling program. Your contribution to the program was significant.

Thank you to all the agronomists, who lined up fields, or producers who offered their fields for the survey. Your contribution can’t be measured.

Thank you very much Jon Williams from Agriculture and Agri-Food Canada for producing this map.

¹Canada’s largest irrigation district faces challenges following another season of drought.

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Wheat midge – Survey and maps

Overview

Methodology

Survey findings

Acknowledgements

Historic survey maps

Resources