Wheat blossom midge: damage characteristics and control timing of this worldwide agricultural pest

The wheat blossom midge is a worldwide agricultural pest, widely distributed in the major wheat-growing countries of Asia, Europe and the Americas. In China there are mainly two species of wheat blossom midge, namely the red blossom midge and the yellow blossom midge. The red wheat blossom midge occurs mainly on both banks of rivers in the plains, while the yellow wheat blossom midge occurs mainly in plateau regions and high mountain zones. Now let us take a look together at the damage characteristics of the wheat blossom midge and the control timing.

I. Morphological characteristics and damage characteristics

The female adult of the red wheat blossom midge has a body length of 2-2.5 mm and a wingspan of about 5 mm, and its body is orange-red. 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 the segments appear like gourd knots, and each swollen part bears a ring of long whorled hairs. The female antennae are bead-like, bearing a ring of short whorled hairs. The male has a body length of about 2 mm. The egg is 0.09 mm long, oblong and light red. The larva has a body length of about 3-3.5 mm, is oval, orange-yellow, with a small head, legless and maggot-shaped, and has a “Y-shaped” sternal spatula on the ventral surface of the prothorax, with a forked front end and a deep depression. The pupa is 2 mm 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: the female has a body length of about 2 mm and a bright yellow body. The egg is 0.29 mm long and banana-shaped. The larva has a body length of 2-2.5 mm, is yellow-green or ginger-yellow, with a smooth body surface; the ventral surface of the prothorax has a sternal spatula, the front end of which is shallowly lobed in an arc shape, and the posterior end of the abdomen bears 2 protrusions. The pupa is bright yellow, with 1 pair of relatively long hairs at the head end.

Both species of blossom midge have one generation per year, and under adverse environmental conditions the larvae have the habit of diapause for many years, so there are also cases of one generation over many years. They overwinter and oversummer as mature larvae in round cocoons in the soil. In the Huang-Huai River basin, 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 of pupal eclosion from late April to early May. After the adults emerge, it is exactly the wheat heading and flowering stage, and they then lay eggs in large numbers (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 the lateral lobes of newly headed wheat plants, laying 5-6 eggs per site, with an egg period of 7-9 days. The red blossom midge mostly lays eggs between the glumes and among the spikelets of wheat ears that have headed but not yet flowered, laying 3-5 eggs per site, with an egg period of 3-5 days. After the larvae hatch, they immediately enter the glumes and attach to the ovary or the just-filling wheat grains to suck sap and cause damage. After feeding, the mature larvae crawl onto the glumes and awns, and with raindrops, dew or by their own springing they fall to the soil surface and burrow into the soil to a depth of 10-20 cm, where they make round cocoons to oversummer and overwinter.

II. Control timing and control techniques

For plots with severe occurrence, control should be carried out at the pupal stage. The control time is the wheat booting stage, April 23-28, using 1.5% methyl parathion 1605 powder 2-3 kg per mu or 1.5% wheat blossom midge absolute kill No. 1 2-3 kg per mu, evenly mixed with 30 kg of fine soil and broadcast on the ground surface; watering after broadcasting gives good control efficacy.

For plots with less severe occurrence, control at the adult stage must be carried out. The control time is the wheat heading stage to before flowering, that is, May 1-10, using 50% phoxim 50 g plus imidacloprid 20-30 g per mu, adding 50 kg of water for spraying, which can control the adult blossom midges and also incidentally control early-generation aphids.

For wheat fields with severe occurrence of blossom midge, it is best to rotate with other crops such as cotton and rapeseed to avoid the source of the pest. Chemical control can adopt the “one broadcast plus one spray” method: from wheat jointing to before booting, use 50% phoxim 0.5-1 kg per mu mixed with 15-20 kg of fine sand and broadcast evenly (water after broadcasting the pesticide) to kill newly emerged adults, larvae and pupae; during the period from after wheat heading to before flowering, then use 4.5% cypermethrin and other pyrethroid pesticides plus 40.7% Lorsban 800-fold mixed solution (20 mL of each per sprayer), or “Hanke 140” 1500-fold solution (10 mL of “Dandayi” per sprayer), which can effectively kill the adults and eggs of the blossom midge, and can simultaneously control wheat aphids and red spiders, controlling multiple pests with one spray, with remarkable control efficacy.