Predicted wheat midge development

Wheat Midge (Sitodiplosis mosellana) – Wheat midge overwinter as larval cocoons in the soil.  Soil moisture conditions in May and June can have significant impact on wheat midge emergence.  Adequate rainfall promotes termination of diapause and movement of larval to the sol surface where pupation occurs.  Insufficient rainfall in May and June can result in delayed movement of larvae to the soil surface. 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. Our wheat midge model (Olfert et al. 2020) indicates that dry conditions may result in:
    a. Delayed adult emergence and oviposition 
    b. Reduced numbers of adults and eggs

As of June 28, 2020, midge model runs indicate that, where midge are present, pupation is occurring across Alberta, northwest Saskatchewan and southern Manitoba (Fig. 1).  Simulations suggest that the first adults might be emerging now (Fig. 2).  

Figure 1. Predicted  percent of population of wheat midge (Sitodiplosis mosellana) at pupal stage across
the Canadian prairies (as of June 28, 2020).

Figure 2. Predicted  percent of population of wheat midge (Sitodiplosis mosellana) at adult stage across
the Canadian prairies (as of June 28, 2020).

Females lay eggs on developing wheat heads.  This typically occurs in evenings when winds are calm. The wheat midge monitoring protocol suggests that wheat fields should be inspected for adults in late June and early July as wheat heads are emerging.  The next three weeks are very important for monitoring wheat midge populations for the purpose of making management decisions.  

Simulations were run to July 21 to assess population development over the next three weeks.  The first two graphs illustrate that adult wheat midge populations near Saskatoon (Fig. 3) and Lacombe (Fig. 4) are expected to emerge on June 30 and July 1, respectively.  

Figure 3. Predicted wheat midge (Sitodiplosis mosellana) phenology at Saskatoon SK projected to July 21, 2020.

Figure 4. Predicted wheat midge (Sitodiplosis mosellana) phenology at Lacombe AB projected to July 21, 2020.

Oviposition will occur soon after adult emergence.  Adult numbers are predicted to peak in mid July (Fig. 3 and 4).  A comparison of the synchrony between wheat midge and wheat is represented in Figure 5 and indicates that adult emergence and oviposition may occur when the crop is most susceptible near Saskatoon.  This information can be used as a guide to determine when fields should be monitored.

Figure 5. Comparison of predicted phenology of wheat midge (Sitodiplosis mosellana) and wheat at Saskatoon SK projected to July 21, 2020.

Information related to wheat midge biology and monitoring can be accessed by linking to your provincial fact sheet (Saskatchewan Agriculture or Alberta Agriculture & Forestry).  A review of wheat midge on the Canadian prairies was published by Elliott, Olfert, and Hartley in 2011.  

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

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.