Introduction to the Latest Control Measures for Wheat Blossom Midge
The wheat blossom midge is a worldwide pest, widely distributed in the major wheat-growing countries of Asia, Europe and the Americas. In China, the wheat blossom midge is also widely distributed across the country's major wheat-producing regions. There are mainly two species of wheat blossom midge in China, namely the red blossom midge and the yellow blossom midge. The red wheat blossom midge occurs mainly on both banks of rivers in plain areas, while the yellow wheat blossom midge occurs mainly in plateau regions and high mountain zones.
Morphological Characteristics
The female adult of the red wheat blossom midge has a body length of 2-2.5mm, a wingspan of about 5mm, and an orange-red body. The forewings are transparent, with 4 well-developed veins, and the hindwings are reduced to halteres. The antennae are slender, with 14 segments; in the male, the middle of each segment is constricted so that each segment appears like a gourd-shaped knot, and the swollen parts each bear a ring of long looped hairs. The female's antennae are bead-like, bearing a ring of short looped hairs. The male has a body length of about 2mm. The egg is 0.09mm long, oblong, and light red. The larva has a body length of about 3-3.5 millimeters, is oval, orange-yellow, with a small head, no legs, and a maggot-like form; on the ventral surface of the prothorax there is a “Y-shaped” sternal spatula, with a forked front end and a deep depression. The pupa is 2mm long, a naked pupa, orange-brown, with 2 short white hairs and 1 pair of long respiratory tubes in front of the head.
The yellow wheat blossom midge female has a body length of about 2mm and a bright yellow body. The egg is 0.29mm long and banana-shaped. The larva has a body length of 2-2.5mm and is yellow-green or ginger-yellow, with a smooth body surface; the ventral surface of the prothorax has a sternal spatula whose front end is shallowly curved and split, and the rear end of the abdomen bears 2 protrusions. The pupa is bright yellow, with 1 pair of relatively long hairs at the head end.
Damage Symptoms
The larvae hide inside the glumes and suck the sap of the filling wheat grains, causing shriveled grains and empty husks. The wheat blossom midge damages the floral organs, kernels and/or wheat grains as larvae, and is a devastating pest.
Damage Characteristics
Both species of blossom midge have one generation per year, and under adverse environmental conditions the larvae have the habit of dormancy for many years, so there are also ones with one generation over many years. They overwinter and oversummer as mature larvae in round cocoons in the soil. In the Huang-Huai River basin, the overwintering larvae break out of their cocoons and rise to the soil surface in early to mid-March, and a large number pupate in mid-to-late April, with the peak emergence of pupae from late April to early May. After the adults appear, it is exactly the wheat heading and flowering stage, and they then lay large numbers of eggs (the yellow blossom midge is slightly earlier than the red wheat blossom midge). The yellow blossom midge mostly lays eggs inside the inner and outer glumes and on their side lobes of newly headed wheat plants, laying 5-6 eggs per spot, with an egg period of 7-9 days. The red blossom midge mostly lays eggs among the glumes and between the spikelets of wheat ears that have headed but not yet flowered, laying 3-5 eggs per spot, with an egg period of 3-5 days. After the larvae hatch, they immediately enter the glumes and attach to the ovary or newly filling wheat grains to suck sap and cause damage. After the mature larvae finish feeding, they crawl onto the glumes and awns, and with raindrops, dew or by their own springing they fall to the soil surface, burrow into the soil to a depth of 10-20 centimeters, and make round cocoons to oversummer and overwinter.
Influencing Factors
1. Temperature. The larvae tolerate low temperatures but not high temperatures, and the overwintering mortality rate is lower than the oversummering one. Overwintering larvae break out of their cocoons and become active when the soil temperature at 10 centimeters is 7℃, pupate at 12℃-15℃, and emerge as adults at 20℃-23℃; when the temperature rises above 30℃, the larvae resume dormancy.
2. Humidity. During the period when overwintering larvae break out of their cocoons, become active and rise to pupate, the emergence rate is higher when there is abundant rain (or irrigation). When humidity is high, not only is the egg hatching rate higher, but the newly hatched larvae are also more active and more likely to invade and cause damage. Abundant rain, high humidity and suitable temperatures around the wheat flowering period often cause major outbreaks of the blossom midge. Droughty weather and low soil moisture are unfavorable to its occurrence.
3. Soil. Loamy soil that is loose and has strong water retention favors its occurrence. Clay soil is unfavorable to its life, and sandy soil is even less suitable for its life. The larvae of the red blossom midge prefer alkaline soil, while the yellow blossom midge prefers relatively acidic soil.
4. When the peak period of adult occurrence coincides with the wheat heading and flowering stage, the occurrence is severe; when the two periods are mismatched, the occurrence is light.
Control Experience
For wheat fields with severe blossom midge occurrence, it is best to rotate with other crops such as cotton and rapeseed to avoid the pest source. Chemical control can adopt the “one spreading plus one spraying” method: from wheat jointing to before booting, use 0.5-1 kg of 50% phoxim per mu mixed with 15-20 kg of fine sand and spread it evenly (water after spreading the pesticide), to kill newly emerged adults, larvae and pupae; during the period from after wheat heading to before flowering, then use a mixed solution of 4.5% cypermethrin and other pyrethroid pesticides plus 40.7% chlorpyrifos at 800 times dilution (20 ml each per sprayer), or “Hanke 140” at 1500 times dilution (10 ml per sprayer, “single-hit”), which can effectively kill the adults and eggs of the blossom midge, and can also simultaneously control wheat aphids and red spiders, controlling multiple pests with one spray, with remarkable control results.
Control Measures
1. Agricultural control
(1) Select insect-resistant varieties
The blossom midge tolerates low temperatures but not high temperatures, so the overwintering mortality rate is lower than the oversummering mortality rate. Soil moisture conditions are an important factor for the overwintering larvae to begin activity, and are a necessary condition for the pupation and emergence of the blossom midge. Different wheat varieties suffer different degrees of damage from the wheat blossom midge; generally, varieties with long and spiny awns, tightly closed and densely arranged spikelets, a short and uniform flowering period, and thick pericarp are unfavorable to the egg-laying, larval invasion and damage of the blossom midge adults.
Therefore, wheat varieties with compact ear shape, long and dense hairs on the inner and outer glumes, thick grain pericarp, and sap that does not easily flow out should be selected.
(2) Crop rotation and stubble changing
Deep plowing of wheat fields year after year, and rotation of wheat with crops such as rapeseed, beans, cotton and rice, have a clear effect on reducing pest populations. In severely affected wheat fields and their surroundings, cotton-wheat intercropping can be implemented or the land can be switched to crops such as rapeseed and garlic, and wheat planted again after a rainy year, which will reduce the damage.
2. Chemical control
(1) Soil treatment
Timing: ① before wheat sowing, at the last shallow plowing; ② at the wheat jointing stage; ③ at the wheat booting stage.
Pesticides: 2% isofenphos-methyl powder, 4.5% jiadi powder, 4% dimethoate-malathion powder, 1.5% methyl 1605 powder (this pesticide is a highly toxic pesticide that has been explicitly banned by the state), using 2-3 kilograms per mu, or 50-100 ml of 80% dichlorvos emulsifiable concentrate added to 1-2 kilograms of water, or 200 ml of 50% phoxim emulsifiable concentrate added to 5 kilograms of water and sprayed onto 20-25 kilograms of fine soil, mixed evenly to make toxic soil for application, spreading while plowing, and turning it into the soil.
(2) Chemical control during the adult stage
From wheat heading to before flowering, use 150 ml of 80% dichlorvos per mu, add 4 kilograms of water to dilute, spray onto 25 kilograms of wheat bran and mix evenly, and spread one pile per mu every other row; this method has a long residual effect and good control results. Or use 40% dimethoate (this pesticide is a highly toxic pesticide that has been explicitly banned by the state) emulsifiable concentrate at 1000 times; 2.5% deltamethrin at 3000 times; 40% fenitrothion wettable powder at 1500 times dilution, etc. for spraying.