The orange wheat blossom midge, Sitodiplosis mosellana, is a recent pest on the prairies.

The adult female midge is a tiny, fragile fly with a distinctively orange abdomen (Olfert et al., 1985). It is

about 3 mm long (about one-third the size of a mosquito). The male midge is smaller. The head is light-brown with 2, large, jet-black eyes. The legs are light-brown and antennas are dark-brown. The wings are oval-shaped, dusky-colored, and fringed with fine hairs.

The orange-colored eggs are tiny, barely visible to the human eye. Newly-hatched larvae are orange-white. The mature larvae are oval-shaped and are orange-red in color.

The pupae are brown and oval-shaped. They are found in the soil, in cocoons smaller than canola seeds.

Spreading from Quebec, where it was first detected in 1628, the orange wheat blossom midge is now found wherever wheat is grown in Canada, including Manitoba.

This midge is typically found in wheat growing areas.

This midge seems to prefer wheat. Other grasses (e.g., barley, rye, wheat grass, couch grass) may also be attacked. Winter wheat is also a host. However, it escapes serious damage if flowering occurs before the eggs are laid and if the kernels are fully developed before the larvae can cause damage. The eggs must be laid before the half-flowering stage for the larvae to survive and damage the kernels.

Adult midges emerge from the soil over a 5-6 week period, from mid-June to mid-July (Elliott, 1988b). This is about the time when the wheat heads are emerging from the sheath and beginning to flower. The midges mate and disperse through the fields (Pivnick and Labbe, 1992). The female midges move downwind above the crop and then drop into the crop canopy and backtrack against the wind to find suitable egg-laying sites.

During warm, calm evenings, female midges lay their eggs on the wheat kernels, singly or in groups of 3-5, under the edge of the glume or in the grooves of spikelets (Reeher, 1945; Mukerji et al, 1988; Pivnick and Labbe, 1992). Female midges lay an average of 30-40 eggs, with a maximum of 100 over their 4- or 5-day life-span.

The eggs hatch in 4-7 days. The young larvae move to the surface of the developing kernels and feed for 2-3 weeks (Doane et al., 1987). The mature larvae remain in the wheat head, each larva enclosed in a transparent skin, until activated by rain or damp weather conditions. Then, these larvae leave the head, drop to the soil surface, and burrow into the soil to form overwintering cocoons. The larvae pass the winter in a resting stage in these cocoons.

The following spring, if the soil is moist and warm, the larvae leave the cocoons, move about in the soil, and pupate near the surface. The adult midges emerge from the pupae about 2 weeks later, completing the cycle. There is only one generation per year.

1. Seasonal Abundance:

Populations are highest after egg-laying is completed, when the wheat is flowering.

Damage is most severe in those areas where soil-moisture in June is high and allows the development

of pupae and emergence of adults. Thus, high population can occur during years with high spring and summer precipitation and warm temperatures.

The duration of egg hatch is affected by temperature, taking as little as 4 day days when warm or as long as 7 days when cool. High humidity, rain, or dew allows the larvae to leave the wheat and move into the soil (Olfert et al., 1985). Temperature can also affect night and ovipositional activity (Pivnick and Labbe, 1992).

If the soil is too dry, overwintering larvae may remain in the cocoons to emerge in subsequent years when moisture conditions are more favorable. The larvae may lie dormant for up to 13 years.

Wheat is most vulnerable to attack if the eggs are laid during the time the heads are about one-half emerged from the boot to half-flowering (when the anthers are exposed). Larval feeding will cause the kernels to shrivel. The more feeding that occurs, the less yield realized (Olfert et al., 1985).

In Manitoba, surveys carried out by Manitoba Agriculture during the 1980's indicate that wheat midge is a perennial but minor pest of wheat, usually causing only minor yield losses. Nevertheless, it has the potential to become a serious pest, given warm, wet conditions during the spring and early summer.

Parasitic wasps (Macroglenes penetrans), attacking the eggs, and mites may offer some long-term control of this insect in dryer wheat-growing regions of the prairies (Doane et al, 1989). Carabid beetles feed on mature larvae, while they are resting in the soil (Floate et al, 1989).

Damage will only be evident when the wheat kernels are separated and the developing seed is inspected. The seed is either undeveloped or shriveled and deformed. The symptoms are similar to those in which the grain has been frozen or affected by drought. Heads (primary heads, first tillers and second tillers) or whole plants can be collected from the field and the heads examined later. Close inspection with a hand-lens and penknife may reveal up to 24 tiny orange larvae feeding on the surface of a single seed.

The spherical larval cocoons or elongate pupal cocoons can be found in the soil by screening soil core samples (Doane et al., 1987). Densities of over 600 cocoons/M² indicate high populations. Up to 8000 cocoons/M² have been observed in outbreak area in Saskatchewan.

Adult midges can be collected by incubating soil samples, containing cocoons, in a glass jar. Adults can be also monitored in the field by up-ending a white pail, coated on the inside with canola oil, over the soil. Periodically, inspect the pails for recently-emerged and trapped adult midges. The sticky yellow cards used by greenhouse operators, mounted on stakes, can also be used in the field to monitor adult midge activity.

On warm, calm evenings, the midges can be observed in the field, laying their eggs on the wheat heads, during the heading stage of wheat growth. Obviously, if these pests are to be detected, the fields must be examined on a daily basis.

1. Threshold/Action Population Level:

Three or 4 maggots per kernel will destroy that kernel. Infestations of 30, 60 and 90% can reduce spring wheat yields by 40, 65 and 80% (Olfert et al, 1935). In Saskatchewan, if 1 or more adult midges are observed for every 4-5 heads, insecticide treatment is recommended.

1. Management Alternatives - Non-Chemical:

Growing alternate crops (e.g., canola, flax or field peas) will prevent a population build-up of wheat midge. Because barley and winter wheat are not as severely damaged as spring wheat, these crops may be grown in areas where infestations are low. Early seeding is recommended to help a crop to develop beyond the susceptible stage, before the files emerge and begin egg-laying. Farmers can seed alternate crops, including barley. Farming practices which promote greater crop uniformity, during heading and flowering (e.g., uniform seeding depth, higher seed rates to reduce tillering), will reduce midge kernel damage. However, chemical management may also be necessary.

Insecticide applications, targeting the adult midges during their flight period, may help to reduce egg-laying and subsequent damage (Elliott, 1988b). The time-frame is short: i.e., for 6-10 days, when the wheat is between the stage of 1/2 head emergence (booting) to 1/2 flowering (anthers exposed) or when about. 80% of the wheat heads are fully-emerged from the boot. Insecticides applied after flowering do not provide adequate control.

Recommended Insecticides usually include the following: i.e.,

Carbofuran (Furadan 480F) 140 21

Chlorpyrifos (Lorsban 4E) 400-480 60

Dimethoate (Cygon 480 EC) 480 21

Carbofuran may be applied by air or ground equipment. It has both systemic and contact action usually with quick results. Furadan 480F is compatible with fungicides commonly used on the same crops. Maybe tank mixed with phenoxy ester or amino herbicides and used only on crops listed on both labels.

When applied 3-6 days after oviposition begins, chlorpyrifos provides about 20-30% better kernel protection than carbofuran or dimethoate (Elliott, 1988a). The latter 2 products provide good control of the adult midge but poor control of the eggs that are already laid.

The treatments should be made in the late afternoon or evening, when temperatures exceed 15C and when the wind speed is less than 10 km/h. If adult midge activity persists for 3-7 days after the treatment, another application may be required.

Thorough coverage of the wheat heads is essential. Application methods which improve the uniformity and amount of spray deposited on wheat heads (i.e., higher water volumes, finer spray droplets, 45 degree nozzle orientation) provide better kernel protection and subsequent grade or yield improvements.

Use the higher rate of chlorpyrifos (Lorsban 4E) for aerial application. High water volumes of 20-35 1/ha are essential. Apply when 70% of the heads have emerged from the boot. When mixing add approximately 1/4 the amount of water required to the spray tank and, with agitation, add the Lorsban 4E. Maintain sufficient agitation during mixing and application. Do not apply or drift on to workers or other persons. Do not apply directly to water or where runoff could occur to adjacent aquatic sites. Avoid use when bees are actively foraging.