Week 11 and our staff are again busy surveying! In fact, it’s appropriate that we take this moment to thank the MANY people who are busy checking traps, doing sweeps, and processing samples! It’s a massive undertaking that happens across the Canadian prairies and begins with dedicated individuals.
Western Canada has one of the most expansive and historically deep data collections in agricultural entomology with grasshopper surveys extending over 100 years and many of our “recent” pests have data sets extending at least 5-40 yrs or more. That amazing data is used in so many ways but it directly supports the development of bioclimatic models for Canada’s most important economic agricultural insect pests and Canadians benefit with predictive model outputs that help growers time and prioritize in-field scouting. It also incrementally improves the ability to estimate insect pest risk from year to year. THANK YOU to everyone who contributes – just “see” how many sites were monitored in 2020!
Be sure to catch the Insect of the Week – it’s swede midge and the canola flower midge: Doppelganger pests!
Stay safe and good scouting to you!
Questions or problems accessing the contents of this Weekly Update? Please contact us so we can connect you to our information. Past “Weekly Updates” can be accessed on our Weekly Update page.
TEMPERATURE: This past week (July 5 – 11, 2021), the prairies continued to experience record-setting temperatures and extremely dry conditions. The warmest temperatures were observed across southern Alberta and Saskatchewan (Fig. 1). Across the prairies, the average 30-day temperature (June 12 – July 11, 2021) was almost 3 °C warmer than climate normal values. The warmest temperatures were observed across southern Alberta and western Saskatchewan (Fig. 2). Southern and western areas of the Peace River region have been 4-5 °C warmer than average.
The 2021 growing season (April 1 – July 4, 2021) has been 1.5 °C warmer than average. The warmest temperatures have occurred across southeastern Manitoba, west-central Saskatchewan and southern Alberta (Fig. 3).
PRECIPITATION: This past week, significant rainfall was reported across southern and central Saskatchewan and Alberta (Fig. 4). Rainfall amounts for the period of June 12 – July 11 (30-day accumulation) have been well below average with most of the prairies receiving less than 40% average (Fig. 5). Growing season (April 1 – July 11) precipitation has been less than average across most of the prairies. Western Saskatchewan and most of Alberta have received less than 100 mm of rain (Fig. 6).
The continued warm temperatures have resulted in the rapid development of wheat midge populations. Where present, wheat midge populations are predicted to be predominantly in the egg stage across most of the prairies (Fig. 1). This is a substantial change from last week where only 12 % of the population was predicted to be in the egg stage. The initial appearance of larvae (in wheat heads) is predicted to be occurring (Fig. 2).
The model was projected to July 27 to determine potential development at Regina (Fig. 3), Lacombe (Fig. 4), and Grande Prairie (Fig. 5) over the next two weeks. The model output suggests that oviposition will continue to increase over the next 5-7 days and should peak sometime this week. Larvae (Sm L1-2) are expected to complete development by the end of July. Macroglenes penetrans, a parasitoid of wheat midge, is active in wheat fields when wheat midge adults are present. Simulation runs indicate that the parasitoid has begun to appear in wheat crops in fields near Regina.
If not already underway, scout for wheat midge adults this week and especially in regions where higher densities are predicted to occur. It is especially important to be monitoring for adults at dusk in regions expected to be at high risk, based on the 2020 survey which is mapped here.
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. 7). 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 the economic threshold decision. Also remember that the parasitoid, Macroglenes penetrans (Fig. 8), 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.
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!
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.
Model simulations were used to estimate grasshopper (Melanoplus sanguinipes) development as of July 11, 2021. Above-average temperatures in late June and early July have resulted in a noticeable increase in grasshopper development. Grasshopper development should be greatest across southern Manitoba where the majority of the population will be in the adult stage (Fig. 1). Adults should be present across all three provinces; more than 13.5 % of the population should be adults.
The long-term average value for this week of the growing season is less than 1% of the population in the adult stage. Development, as of July 11, 2021, is well ahead of long-term average values (Fig. 3).
Grasshopper Scouting Steps: ● Review grasshopper diversity and scouting information including photos of nymphs, adults, and non-grasshopper species to aid in-field scouting and accurately apply thresholds for grasshoppers. ● Measure off a distance of 50 m on the level road surface and mark both starting and finishing points using markers or specific posts on the field margin. ● Start at one end in either the field or the roadside and walk toward the other end of the 50 m, making some disturbance with your feet to encourage any grasshoppers to jump. ● Grasshoppers that jump/fly through the field of view within a one-meter width in front of the observer are counted. ● A meter stick can be carried as a visual tool to give perspective for a one-meter width. However, after a few stops, one can often visualize the necessary width and a meter stick may not be required. Also, a hand-held counter can be useful in counting while the observer counts off the required distance. ● At the endpoint, the total number of grasshoppers is divided by 50 to give an average per meter. For 100 m, repeat this procedure. ● Compare counts to the following damage levels associated with pest species of grasshoppers: 0-2 per m² – None to very light damage 2-4 per m² – Very light damage 4-8 per m² – Light damage 8-12 per m² – Action threshold in cereals and canola 12-24 per m² – Severe damage 24 per m² – Very severe damage For lentils at flowering and pod stages, >2 per m² will cause yield loss. For flax at boll stages, >2 per m² will cause yield loss. ● More practically, the following thresholds are offered but, in the event of additional crop stress (e.g., drought), the use of “may be required” versus “control usually required” requires careful consideration:
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season. Diamondback moth was the Insect of the Week for Wk10!
Model simulations to July 11, 2021, indicate that the second generation of non-migrant adults are currently emerging across the Canadian prairies (Fig. 1). A third generation is predicted for southern Manitoba. Based on climate normal inputs, development is well ahead of long-term average values (Figure 2). Based on current weather, the mean number of generations that have occurred is 2.1 compared to model runs, based on climate normals, predict that the number of generations should be 1.4.
Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 2) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Provincial insect pest monitoring networks in Manitoba, Saskatchewan and Alberta are now compiling cumulative counts of adults intercepted from the pheromone-baited green unitraps deployed in fields across the prairies. Review the Provincial Insect Pest Report Links to find summaries or link to the latest bertha armyworm moth counts by clicking the appropriate province’s reporting info for Manitoba, Saskatchewan or Alberta. So far, interception counts remain mainly in the “low risk” categories across the Canadian prairies. Review the 2020 pheromone trapping cumulative moth counts here to identify potential high risk areas to target for scouting for larvae now!
The Insect of the Week features Swede midge and the canola flower midge as doppelganger pests this week!
Two species of midges (Diptera: Cecidmyiidae) are known to infest canola in Canada. Since 2000, swede midge (Contarinia nasturtii) has been established in southern Ontario with serious levels of damage observed in several species of Brassicaceae, including canola by 2003. Swede midge is also established in Quebec, Nova Scotia, and Prince Edward Island. Across the prairie region of Canada, a separate canola flower midge (Contarinia brassicola Sinclair) was identified initially as larvae feeding within the developing flower that caused the formation of a “pop-bottle”-shaped gall (Fig. 1). To date, this is the only damage associated with the canola flower midge, and it has been minimal across the prairies.
Because of the serious threat that swede midge poses to canola production, it is vital that monitoring for swede midge continues across the Prairies. Monitoring is underway for 2021.
Tips for scouting canola for midges: • Watch for unusual plant structures and plant discolourations then follow-up by closely scrutinizing the plant for larvae. • The growing tip may become distorted and produce several growing tips or none at all, young leaves may become swollen, crinkled or crumpled and brown scarring caused by larval feeding may be seen on the leaf petioles and stems. • Flowers may fail to open. • Young plants that show unusual growth habits should be examined carefully for damage and larvae; especially if the sticky liners have many flies resembling midges (swede midges are about the size of orange blossom wheat midge but are not orange). • Larvae can be seen with a hand lens.
The following is offered to help predict when Culex tarsalis, the vector for West Nile Virus, will begin to fly across the Canadian prairies. This week, regions most advanced in degree-day accumulations for Culex tarsalis are shown in Figure 1 but the unusual heat across the prairies greatly accelerated mosquito development!
As of July 11, 2021 (Fig. 1), C. tarsalis development continues to be most advanced in Manitoba, southern Alberta, and in a small pocket in southern Saskatchewan. The map will change very quickly to red (i.e., areas with sufficient heat accumulation for C. tarsalis to emerge). Areas highlighted yellow or orange in the map below (as of July 11) should start to use DEET this week! IF C. tarsalis is present in an area where WNV is active, it may take as little as 12 days for adults to become fully infective with the current warm weather.
Anyone keen to identify mosquitoes will enjoy this pictorial key for both larvae and adults which is posted on the Centre for Disease Control (CDC) website but sadly lacks a formal citation other than “MOSQUITOES: CHARACTERISTICS OF ANOPHELINES AND CULICINES prepared by Kent S. Littig and Chester J. Stojanovich” and includes Pages 134-150. The proper citation may be Stojanovich, Chester J. & Louisiana Mosquito Control Association. (1982). Mosquito control training manual. pp 152.
Provincial entomologists provide insect pest updates throughout the growing season so link to their information:
MANITOBA’SCrop Pest Updates for 2021 are now available – access the July 14, 2021 report here. Be sure to bookmark their Crop Pest Update Index to readily access these reports! Bookmark their insect pest homepage to access fact sheets and more! • Bertha armyworm pheromone trap monitoring update for MB – Cumulative counts arising from weekly data are available here. The initial counts are categorized as “low risk” so far (i.e., 0-300 moths). • Diamondback moth pheromone trap monitoring update for MB – Trapping has drawn to a close for 2021. Access the summary here. Only 65 traps intercepted moths and the highest cumulative count was 171 moths near Selkirk. Access the summary (as of June 30, 2021). At this point, in-field scouting for larvae remains important.
ALBERTA’SInsect Pest Monitoring Network webpage links to insect survey maps, live feed maps, and insect trap set-up videos and more. There is also a Major Crops Insect webpage. The new webpage does not replace the Insect Pest Monitoring Network page. Remember, AAF’s Agri-News occasionally includes insect-related information or Twitter users can connect to #ABBugChat Wednesdays at 10:00 am. • Wheat midge pheromone trap monitoring update for AB – Cumulative counts arising from weekly data are available so refer to the Live Map. Some sites in central Alberta are beginning to report “high risk” adult counts so synchrony with anthesis will need to be carefully monitored(08Jul2021). • Cabbage seedpod weevil sweep-net monitoring update for AB – In-field counts can be entered here to populate the Live Map. Some sites in southern Alberta are reporting densities at or above the economic threshold in canola (08Jul2021). • Bertha armyworm pheromone trap monitoring update for AB – Cumulative counts arising from weekly data have begun so refer to the Live Map. Cumulative counts throughout the province report “low risk” numbers of moths so far (08Jul2021). • Diamondback moth pheromone trap monitoring update for AB – Trapping has drawn to a close for 2021. Refer to the Live Map which reports extremely low numbers of moths intercepted so far (<50 province-wide as of 01Jul2021). At this point, in-field scouting for larvae remains important. • Cutworm reporting tool – Refer to the Live Map which now reports seven sites with cutworms (as of 01Jul2021).
In 2016, entomologists on the Canadian Prairies identified a previously unknown species of midge while conducting field experiments in northeastern Saskatchewan. The new midge was described in 2019 and is named Contarinia brassicola Sinclair (Diptera: Cecidomyiidae). It is known unofficially as the canola flower midge, although its host range includes mustard varieties.
The full extent of the host range of canola flower midge has yet to be studied. Field surveys conducted between 2017 and 2019 found that the canola flower midge is widely distributed in Alberta, Saskatchewan, and Manitoba, with some pockets of higher population densities (i.e., northeastern Saskatchewan). The canola flower midge is morphologically similar to the swede midge: a doppelganger insect that damages the same field crops that canola flower midge does, as well as a variety of cruciferous vegetables (e.g., cabbage, cauliflower, Brussels sprouts) and Brassica weeds. Both species have much in common, but differences in the type of plant damage they inflect can help distinguish between the two.
Neither insect poses a threat to crops in their adult form, but both species have larvae that cause damage to their host plants. Canola flower midge larvae consume individual canola buds, resulting in characteristic galled flowers. In comparison, swede midge larvae are known to attack and consume plant material at any growing point on their host plants, affecting normal plant development.
Both midge species are quite similar in their physical characteristics. Adults are delicate, 2–5 mm long flies ranging in colour from light brown to grey. These insects have long legs, long beaded antennae and sparse venation on their wings. Larvae grow between 3–4 mm long. Young larvae are semi-translucent when they hatch and turn yellow as they mature.