Predicted wheat midge development (June 20, 2019; Wk 11)

Wheat Midge (Sitodiplosis mosellana) – Wheat midge adults generally emerge during the first week of July. Compared to long term normal values for temperature and rainfall, May and June in the Saskatoon region has been approximately 1 °C cooler and rainfall is 40-60% less than normal. Dry conditions in May and June can have significant impact on midge emergence. Elliott et al (2009) reported that wheat midge emergence was delayed or erratic, if rainfall did not exceed  20-30 mm  during May.  

Olfert et al. 2016 ran model simulations to demonstrate how rainfall impacts wheat midge population density. Two simulations were run to demonstrate the impact of rainfall and temperature on adult emergence and oviposition. The first graph illustrates adult emergence and oviposition based on long term (climate) data for Saskatoon (Fig. 1). The model indicates that emergence should begin in early July with oviposition beginning a few days later. 

Figure 1. Predicted adult emergence and oviposition of wheat midge (Sitodiplosis mosellana) based on LONG TERM DATA for Saskatoon SK.

The second graph (Fig. 2) shows how DRYER, COOLER conditions would result in:
   a. Delayed adult emergence and oviposition.
   b. Reduced numbers of adults and eggs.

Figure 2. Predicted adult emergence and oviposition of wheat midge (Sitodiplosis mosellana) using LONG TERM DATA manipulated to both DRYER and COOLER conditions for Saskatoon SK.

Monitoring:
When monitoring wheat fields, pay attention to the synchrony between flying midge and anthesis.  
• In-field monitoring for wheat midge should be carried out in the evening (preferably after 8:30 pm or later) when the female midges are most active. 
• On warm (at least 15ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads (Fig. 3). 
• Midge populations can be estimated by counting the number of adults present on 4 or 5 wheat heads. 
• Inspect the field daily in at least 3 or 4 locations during the evening.

Figure 3. Adult wheat midge (Sitodoplosis mosellana) active on wheat head at anthesis stage
(Photo: AAFC-Beaverlodge; S. Dufton and A. Jorgensen).

REMEMBER in-field counts of wheat midge per head remain the basis of economic threshold decision.  Also remember the parasitoid, Macroglenes penetrans (Fig. 4), is actively searching for wheat midge at the same time. Preserve this parasitoid whenever possible and remember your insecticide control options for wheat midge also kill beneficial insects that help regulate midge populations.

Figure 4. The tiny parasitoid wasp, Macroglenes penetrans, is synchronized to emerge when wheat midge adults are present and the wasp seeks and oviposits on wheat midge eggs (Photo: AAFC-Beaverlodge; S. Dufton).

Economic Thresholds for Wheat Midge:
a) To maintain optimum grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage.

b) For yield only: 1 adult midge per 4 to 5 heads. At this level of infestation, wheat yields will be reduced by approximately 15% if the midge is not controlled.

Inspect the developing kernels for the presence of larvae and the larval damage. 

Information related to wheat midge biology and monitoring can be accessed by linking to your provincial fact sheet (Saskatchewan Agriculture, Alberta Agriculture & Forestry) or access the Prairie Pest Monitoring Network's monitoring protocol recently updated by Wist et al. 2019.  A review of wheat midge on the Canadian prairies was published by Elliott, Olfert, and Hartley in 2011.  

Alberta Agriculture and Forestry has also released a YouTube video describing in-field monitoring for wheat midge this week.  

More information about Wheat midge can be found by accessing the pages from the new "Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide".  View ONLY the Wheat midge pages but remember the guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.