On this page
How to identify it
- The adult is a very small, fragile orange fly about half the size of a mosquito, 2 to 3 millimeters (about 1/8 inch) long. Two large black eyes cover much of its brown head, its legs are long for its size, and its oval, clear wings are fringed with fine hairs.[1][2]
- It is active in the evening. Midges flutter from plant to plant and rest with the head pointing up.[1][2]
- The larvae are small orange maggots, 2 to 3 millimeters long when grown, found on the surface of developing kernels inside the florets, often three or four per floret.[1][2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Lauxaniid flies | Some lauxaniid flies common in wheat, such as Camptoprosopella borealis, are a little larger (2.5 to 4 millimeters) and yellowish-brown rather than orange. They rest on leaves and awns during the day, fly above the crop when disturbed, and sit level or head-down instead of head-up.[1][2] |
Where it lives
It is found around the world wherever wheat is grown. Significant damage has been reported in Minnesota, North Dakota and Idaho, and in Alberta, Saskatchewan, Manitoba and British Columbia.[2][1]
Biology and life cycle
There is one generation a year. Larvae spend the winter in round cocoons in the soil, mostly in the top 5 centimeters (2 inches), and can stay dormant until the next spring or for several years until conditions suit them.[1][2]
In spring the larvae move to the soil surface to pupate, and adults emerge in late June or early July; emergence can continue for about six weeks. Moist soil in May and June is needed for development, and in Manitoba the flight peaks in mid-July.[1][2]
During the day adults stay in the humid crop canopy. In the evening, females move to the top of the canopy and lay eggs on newly emerged wheat heads, singly or in groups of three or four under the glumes or in grooves on the florets. A female lives less than a week and lays about 80 eggs. Most egg laying happens from about 75 minutes before to 30 minutes after sunset, when it is warmer than 15 C (59 F) and the wind is under 10 km/h (6 mph).[1][2]
Eggs hatch in four to seven days, and the larvae feed for two to three weeks before dropping to the soil. In dry weather they can shrink inside their last larval skin and wait, in Manitoba's account for up to two months, until moisture lets them move on.[1][2]
Besides wheat it feeds on barley, couch grass, intermediate wheatgrass and rye, though infestations on these are usually not serious enough to need control.[1][2]
Damage and signs
- Only the larvae do damage. They feed on the developing kernel by releasing enzymes that break down the cell walls and turn starch into sugars, which leaves the kernel shriveled, cracked and deformed.[1][2]
- Damage varies within a head: some kernels are aborted, some are so small and light they pass through the combine with the chaff, some are only slightly damaged and some are untouched. Lost kernels reduce yield, and damaged ones lower the grade.[1][2]
- The head shows no change in color, size or shape, so the damage can only be found by opening the florets and looking at the seed. Populations can stay low for years and then build to epidemic levels quickly.[1][2]
- Uncontrolled, about one adult midge per four or five heads reduces yield by roughly 15 percent, and higher densities cut it further.[2]
Health risk
These agricultural sources treat it only as a wheat pest and do not mention any harm to people.[1][2]
Control
Prevention
Avoid growing wheat after wheat. Where midge numbers in the soil are high, switch to crops it does not damage, such as oilseeds and pulses; barley, oats and annual canary grass can also be grown with little or no risk.[1][2]
Midge-tolerant wheat varieties are available in Canada as blends that include 10 percent of a susceptible variety as a refuge, a step meant to reduce the risk that the midge develops resistance to them.[1]
Seeding date results have been mixed. Early seeding of early-maturing spring wheat at higher seeding rates can let the crop head and flower before the midge peaks, but Alberta trials found that some newer, longer-heading spring wheat and durum varieties had the least damage when seeded late.[1][2]
Biological control
A tiny parasitic wasp, Macroglenes penetrans, lays its eggs in wheat midge eggs and kills the larva the following spring; under natural conditions it controls about 40 percent of the overwintering midge population each year. Parasitized larvae still damage the current crop, so the benefit shows up the next year. Ground beetles also eat midge larvae in the soil.[1][2]
Pesticides
An insecticide is economical only when the threshold is reached after the heads emerge and before the crop flowers. Spraying during advanced flowering is discouraged because the crop is no longer susceptible and the spray harms the parasitic wasps. Apply in the evening, when females are at the top of the canopy. In Canada, Manitoba Agriculture lists dimethoate as the only registered insecticide; it kills adults but not eggs and should go on within 24 hours of reaching the threshold.[1][2]
Numbers are often highest along field edges, and when they drop off sharply toward the middle, treating only the margins may be enough.[2]
Scouting and thresholds
Wheat is most at risk when eggs are laid during heading; kernel damage falls 15- to 25-fold between late heading and early flowering. Check fields often from the time heads emerge from the boot until anthers show.[2][1]
Scout in the evening, from about 75 minutes before to 30 minutes after sunset, when it is warmer than 15 C and calm. Count the adults on four or five heads at three or four spots in the field. Densities are often highest next to last year's wheat fields and in low, moist spots.[1][2]
Suggested thresholds are one adult per four or five heads when yield is the only concern, and one per eight to ten heads when keeping the top grade matters.[1][2]
In Manitoba, yellow sticky cards set at head height can stand in for evening counts: ten traps 10 meters apart, collected after three evenings, with an action threshold of three or four midges per ten traps. Emergence can also be forecast from degree-days above 5 C, with half the adults out at about 784 degree-days.[1]
Common questions
- My wheat heads looked fine, so why are the kernels shriveled?
- Wheat midge larvae feed inside the florets without changing the head's color, size or shape, so the damage is often mistaken for frost or drought. Open the florets during kernel development and look for small orange larvae.[1][2]
- When should I check my wheat for midge?
- From the time heads emerge until anthers appear, in the evening around sunset on warm, calm days, when the females are laying eggs at the top of the canopy.[1][2]
Sources
- Manitoba Agriculture, Government of Manitoba, “Wheat Midge (fact sheet; J. Gavloski, revised May 2024).” www.gov.mb.ca/agriculture/crops/insects/pubs/wheat-midge-factsheet-revised-may2024.pdf (accessed 2026-11-09)
- Government of Alberta, “Wheat midge: Overview.” www.alberta.ca/wheat-midge-overview (accessed 2026-11-09)
- iNaturalist, “Sitodiplosis mosellana taxon page (order and family).” www.inaturalist.org/taxa/130249 (accessed 2026-11-09)