Macroglenes penetrans is a beneficial parasitoid wasp from the family Pteromalidae. It is an important natural enemy of wheat midge. This small, black wasp can be seen emerging in large numbers from wheat stubble shortly after wheat midge adults are first sighted. This means that often they are emerging into canola fields and then have to disperse to find wheat fields where their hosts are active. Macroglenes penetrans is a parasitoid that lives inside the wheat midge larva and overwinters within the wheat midge larval cocoon. In the spring, the parasitoid larva develops to emerge from the wheat midge cocoon buried in the soil and then the adult parasitoid seeks out wheat midge eggs.
A very small adult Macroglenes penetrans on a wheat head. Picture credit: Shelby Dufton, AAFC Beaverlodge Research Farm.
Macroglenes penetrans is an important part of wheat midge management – parasitism rates can reach upwards of 70% of the wheat midge population! The numbers of this parasitoid overwintering inside wheat midge cocoons are counted during the fall soil core survey, so that the survey map only includes counts of non-parasitized wheat midge.
The following maps represent predicted regional estimates of wheat midge development. Remember – field level populations are assessed only through in-field scouting.
As of July 24, 2022, where wheat midge is present, model simulations predict that Albertan populations should be primarily in the egg stage, while populations across Manitoba and eastern Saskatchewan should consist of larvae developing in wheat heads (Fig. 1).
Figure 1. Wheat midge larvae (AAFC)
Regional differences in wheat midge development can be attributed to rainfall differences that occurred in May and June. Optimal rainfall in May and June across Saskatchewan and Manitoba has resulted in faster rates of wheat midge development rates than in Alberta. As a result, some adult wheat midge may still be active in Alberta (Fig. 2), while adult populations should have peaked and should be declining across Saskatchewan and Manitoba. Populations in the Peace River region are predicted to be primarily in the egg stage (Fig. 3). Across Manitoba and Saskatchewan, populations are predicted to be transitioning from the egg stage to the larval stage (Fig. 4). Wheat midge developmental rates near Regina, Saskatchewan are predicted to be greater than for Grande Prairie, Alberta.
Figure 2. Percent of wheat midge larval population (Sitodiplosis mosellana) that is in the adult stage, across western Canada,as of July 24, 2022.Figure. 3. Percent of wheat midge population (Sitodiplosis mosellana) that is in the egg stage across western Canada, as of July 24, 2022.Figure 4. Percent of wheat midge population (Sitodiplosis mosellana) that is in the larval stage (in wheat heads), across western Canada, as of July 24, 2022.
Model simulations indicate that egg development is complete and populations are primarily in the larval stage (>90%) for populations near Regina (Fig. 5) while Grande Prairie populations are predicted be in both egg (31%) and larval stages (61%) (Fig. 6). Potential risk continues to be greatest across eastern Saskatchewan and Manitoba.
Figure 5. Predicted development of wheat midge (Sitodiplosis mosellana) and wheat development near Regina, Saskatchewanas of July 24, 2022. Figure 6. Predicted development of wheat midge (Sitodiplosis mosellana) and wheat development near Grande Prairie, Alberta,as of July 24, 2022.
In-Field Monitoring:The window for scouting and application of the economic threshold for wheat midge (i.e., during the synchrony between wheat anthesis and midge flight period) has now drawn to a close for 2022.
Additional information can be accessed by reviewing the Wheat midge pages extracted from the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
The following maps represent predicted regional estimates of wheat midge development. Remember – the rate of development and density varies at the field level and can only be verified through in-field scouting. Midge flight coinciding with the beginning of anthesis is a crucial point when in-field counts of adults on plants are carefully compared to the economic thresholds!
As of July 17, 2022, where wheat midge are present, model simulations predict that eggs and larvae (in heads) are the two prevalent stages occurring across the prairies. Differences in wheat midge development are attributed to rainfall differences across the prairies. Optimal rain events in May and June across Saskatchewan and Manitoba have contributed towards and advanced development rates of WM populations whereas populations in southern and central Alberta remain largely in the adult stage (Fig. 1). Adult populations in Saskatchewan and Manitoba are predicted to have peaked and are declining. Populations in the Peace River region are predicted to be primarily in the egg stage (Fig. 2). Across Manitoba and Saskatchewan, populations are predicted to be transitioning from the egg stage to the larval stage (Fig. 3).
Figure 1. Percent of wheat midge larval population (Sitodiplosis mosellana) that is in the pupal stage, across western Canada,as of July 17, 2022.Figure. 2. Percent of wheat midge population (Sitodiplosis mosellana) that is in the egg stage across western Canada, as of July 17, 2022.Figure 3. Percent of wheat midge population (Sitodiplosis mosellana) that is in the larval stage (in wheat heads), across western Canada, as of July 17, 2022.
Wheat midge development can be very site specific. For example, (as of July 17, 2022) developmental rates near Regina, Saskatchewan were predicted to be greater than for Yorkton, Saskatchewan, and Grande Prairie, Alberta. Model simulations indicate that populations near Regina were predominantly in the larval stage (Fig. 4) while Yorkton and Grande Prairie populations were predicted to be predominantly eggs (Figs. 5 and 6).
Figure 4. Predicted development of wheat midge (Sitodiplosis mosellana) and wheat development near Regina, Saskatchewanas of July 17, 2022.Figure 5. Predicted development of wheat midge (Sitodiplosis mosellana) and wheat development near Yorkton, Saskatchewanas of July 17, 2022. Figure 6. Predicted development of wheat midge (Sitodiplosis mosellana) and wheat development near Grande Prairie, Alberta,as of July 17, 2022.
In-Field Monitoring:When scouting 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 15 ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads (Fig. 5). 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 5. Wheat midge (Sitodiplosis mosellana) laying their eggs on a wheat head. Photo: AAFC-Beav-S. Dufton and A. Jorgensen.
REMEMBER that in-field counts of wheat midge per head remain the basis of the economic threshold decision. Also remember that the parasitoid, Macroglenes penetrans (Fig. 6), is actively searching for wheat midge at the same time. Preserve this parasitoid whenever possible and remember insecticide control options for wheat midge also kill these beneficial insects who help reduce midge populations.
Figure 6. Macroglenes penetrans, a parasitoid wasp that attacks wheat midge, measures only ~2 mm long. Photo: AAFC-Beav-S. Dufton.
Economic Thresholds for Wheat Midge: a) To maintain optimum No. 1 grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage. b) To maintain 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 larval damage.
Wheat midge was featured as the Insect of the Week in 2021 (for Wk07). Be sure to also review wheat midge and its doppelganger, the lauxanid fly, featured as the Insect of the Week in 2019 (for Wk11) – find descriptions and photos to help with in-field scouting! Additionally, the differences between midges and parasitoid wasps were featured as the Insect of the Week in 2019 (for Wk12). Remember – 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 OR pollinators that perform valuable ecosystem services!
Additional information can be accessed by reviewing the Wheat midge pages extracted from the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Soil moisture conditions in May and June can have significant impacts on wheat midge emergence. Where wheat midge cocoons are present in soil, the 2022 growing season’s rainfall during May and June should be sufficient to terminate diapause and induce the larvae to move to the soil surface.
The map in Figure 1 provides a visual representation of regional estimates of wheat midge movement to the soil surface, where pupal development will occur, then adults will begin to emerge. Remember – the rate of development and timing of adult midge emergence varies at the field level and can only be verified through in-field scouting. Fields within regions receiving sufficient rainfall should scout! Midge flight coinciding with the beginning of anthesis is a crucial point when in-field counts of adults on plants are carefully compared to the economic thresholds.
As of July 3, 2022, model simulations predict that larvae (surface) and pupae are present with increased occurrence of adults. Larvae are completing development and transitioning to the pupal stage. Compared to last week, pupal populations are predicted to increase across the Parkland and Peace River regions (Fig. 1). Appearance of adults is predicted to increase across eastern Saskatchewan and southern Manitoba (Fig. 2). Occurrence of adults may be occurring when wheat is most susceptible. Occurrence of adults and eggs (top panel) are predicted to occur when wheat is heading (bottom panel) for fields near Regina, Saskatchewan (Fig. 3). Phenology simulations suggest that wheat may be susceptible for the next 10-12 days.
Figure 1. Percent of wheat midge larval population (Sitodiplosis mosellana) that is in the pupal stage, across western Canada,as of July 3, 2022.Figure. 2. Percent of wheat midge population (Sitodiplosis mosellana) that is in the adult stage, across western Canada, as of July 3, 2022.Figure 3. Predicted development of wheat midge (Sitodiplosis mosellana) and wheat development near Regina, Saskatchewanas of July 3, 2022.
In-Field Monitoring:When scouting 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 15 ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads (Fig. 4). 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 4. Wheat midge (Sitodiplosis mosellana) laying their eggs on a wheat head. Photo: AAFC-Beav-S. Dufton and A. Jorgensen.
REMEMBER that in-field counts of wheat midge per head remain the basis of the economic threshold decision. Also remember that the parasitoid, Macroglenes penetrans (Fig. 5), is actively searching for wheat midge at the same time. Preserve this parasitoid whenever possible and remember insecticide control options for wheat midge also kill these beneficial insects who help reduce midge populations.
Figure 5. Macroglenes penetrans, a parasitoid wasp that attacks wheat midge, measures only ~2 mm long. Photo: AAFC-Beav-S. Dufton.
Economic Thresholds for Wheat Midge: a) To maintain optimum No. 1 grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage. b) To maintain 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 larval damage.
Wheat midge was featured as the Insect of the Week in 2021 (for Wk07). Be sure to also review wheat midge and its doppelganger, the lauxanid fly, featured as the Insect of the Week in 2019 (for Wk11) – find descriptions and photos to help with in-field scouting! Additionally, the differences between midges and parasitoid wasps were featured as the Insect of the Week in 2019 (for Wk12). Remember – 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 OR pollinators that perform valuable ecosystem services!
Additional information can be accessed by reviewing the Wheat midge pages extracted from the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
The Field Heroes campaign continues to raise awareness of the role of beneficial insects in western Canadian crops. Check the recently updated Field Heroes website for scouting guides, downloadable posters, and videos. Learn about these important organisms at work in your fields!
Two NEW Field Heroes resources for 2021 include:
The NEW Pests and Predators Field Guideis filled with helpful images for quick insect identification and plenty of tips to manage the pests AND natural enemies in your fields. Claim your free copy at http://fieldheroes.ca/fieldguide/ or download for free to arm your in-field scouting efforts!
This week’s Insect of the Week is a beneficial wasp from the Family Pteromalidae named Macroglenes penetrans. It is an important natural enemy of wheat midge. The wasp is a parasitoid that lives within the wheat midge larva and overwinters within the host. In the spring, the parasitoid larva develops to emerge from the wheat midge cocoon buried in the soil and seeks out wheat midge eggs.
For more information about M. penetrans, see our Insect of the Week page.
Macroglenes penetrans – adult (AAFC)
Follow @FieldHeroes to learn more about Natural Enemies that are working for you for FREE to protect your crops!
Wheat Midge (Sitodiplosis mosellana) – Predictive modelling will be used again to help forecast wheat midge emergence across the Canadian prairies. The map below predicts the geographic distribution and corresponding accumulation of heat units necessary for wheat midge to emerge from puparia developing in the soil.
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 growers in Alberta can access mapped cumulative counts from wheat midge pheromone traps. A screen shot of the map is provided below (retrieved August 3, 2016).
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.
Wheat Midge (Sitodiplosis mosellana) – Predictive modelling will be used again to help forecast wheat midge emergence across the Canadian prairies. The map below predicts the geographic distribution and corresponding accumulation of heat units necessary for wheat midge to emerge from puparia developing in the soil.
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 growers in Alberta can access mapped cumulative counts from wheat midge pheromone traps. A screen shot of the map is provided below (retrieved 27Jul2016).
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.
