Thursday, 25 June 2020

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 21, 2020, wheat midge model runs indicate that recent rainfall in Manitoba should result in development of wheat midge larvae (between Brandon and Winnipeg).  These larvae (in the soil) are expected to be moving to the soil surface.  Dry conditions across eastern Saskatchewan has delayed development of larval cocoons.  Pupae are predicted to be appearing across Alberta.  
Figure 1. Predicted  percent of larval population of wheat midge (Sitodiplosis mosellana) at soil surface across
the Canadian prairies (as of June 21, 2020).

Figure 2. Predicted  percent of population of wheat midge (Sitodiplosis mosellana) at pupal stage across
the Canadian prairies (as of June 21, 2020).

The following graph illustrates that adult wheat midge populations in the Saskatoon area are expected to emerge on June 30th.  Peak adult numbers are predicted to peak in mid July.  Females lay eggs on developing wheat heads. This typically occurs in the evening 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.  

Figure 3. Projected wheat midge (Sitdiplosis mosellana) phenology at Saskatoon SK as of June 30, 2020.

The following table provides an estimate of first occurrence of wheat midge adults and can be used as a guide to determine when fields should be monitored. 

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.