Wheat midge (July 11, 2019; Wk 14)

Wheat Midge (Sitodiplosis mosellana) – Where wheat midge are present, cool, dry conditions have resulted in delayed emergence of adults. Wheat midge larvae have moved to the soil surface and pupae are appearing.  In some locations adults should be beginning to emerge. The wheat midge model predicts that 45% (54% last week) of the population are in the larval  cocoon stage and 47% (42% last week) of the population is predicted to have moved to the soil surface. This week 7% (3.4% last week) is predicted to be in the pupal stage. Adults have begun to emerge in localized areas in southern AB and MB. 

The first map indicates the percent of the population that is in the larval stage, at the soil surface.  Midge development in SK was reduced due to dry soil moisture conditions. The second map indicates that pupae may be present in some fields in southern AB and MB. It should be noted that, based on fall surveys in 2018, wheat midge populations were expected to be low across most of AB and SK.

Figure 1.  Percent of larval population at the soil surface (as of July 8, 2019) across the Canadian prairies.

Figure 2. Percent of  population AT PUPAL STAGE (as of July 8, 2019) across the Canadian prairies.

 

Figure 3. Percent of  population AT ADULT STAGE (as of July 8, 2019) across the Canadian prairies.

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 (photographed by AAFC-Beav-S. Dufton & A. Jorgensen below). 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.

REMEMBER that in-field counts of wheat midge per head remain the basis of economic threshold decision.  Also remember that the parasitoid, Macroglenes penetrans (photographed by AAFC-Beav-S. Dufton below), 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 these beneficial insects which help reduce midge populations.

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. 

Wheat midge and its doppelganger, the lauxanid fly, were featured as the Insect of the Week (for Wk10).  Check that post for help with in-field scouting for this economic pest of wheat!  The differences between midges and parasitoid wasps are featured as the current Insect of the Week (for Wk11).  Not all flying insects are mosquitoes nor are they pests - many are important parasitoid wasps that actually regulate insect pest species in our field crops.

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.  

NEW - 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.