Wheat stem maggot

Scientific name Meromyza saltatrix Linnaeus, order Diptera, family Chloropidae. It is distributed from Heilongjiang, Inner Mongolia, ** in the north, south to Guizhou and Yunnan, and west to ** and Tibet. It also occurs in Hainan in Qinghai and the Garze and Aba regions of Sichuan. Damage is more severe in **, Inner Mongolia, Ningxia, as well as parts of Hebei, Shanxi, Shaanxi, and Gansu.

Hosts @#@245@#@, barley, oats, alkali grass, cogongrass, etc.

Damage characteristics: the larvae bore into the stems of wheat and other hosts to feed. Newly hatched larvae enter the wheat stem from the leaf sheath or between stem nodes, or bore downward in a spiral at the young heart leaf and the basal 1/5 to 1/4 of the ear node, causing dead heart, white heads, and rotten heads, with no grain set.

Morphological characteristics: male adult body length 3-3.5 mm, female 3.7-4.5 mm, body light yellow-green, compound eyes black, thorax dorsum with 3 black or dark brown longitudinal stripes; the middle stripe is broad in front and narrow behind, directly connecting to the end of the posterior prismatic area, while the lateral stripes are only half or a little more than half the length of the middle stripe and forked at the end. Antennae yellow, palps black with yellow base. Legs yellow-green. Hind femora enlarged. Egg length 1 mm, spindle-shaped, white, with 10 longitudinal striations on the surface. Mature larva body length 6-6.5 mm, yellow-green or pale yellow-green, maggot-shaped. Pupa is a coarctate pupa; male body length 4.3-4.7 mm, female 5-5.3 mm; puparium transparent, with compound eyes, thorax, abdomen, etc. visible.

Life habits: in spring wheat areas such as Inner Mongolia it has 2 generations per year, and in winter wheat areas 3-4 generations per year, overwintering as larvae at the root crown of hosts, in soil crevices, or on weeds. In spring wheat areas, overwintering-generation adults first appear in early to mid-May of the following year, enter the peak occurrence period in late May and early June, and the egg-laying peak is in mid to late June; eggs hatch after 4-7 days, and late June is the peak period of larval damage, lasting about 20 days. Pupation occurs in early to mid-July, with the pupal stage lasting 5-10 days. Most first-generation larvae emerge before wheat harvest in mid to late July and leave the wheat field, laying eggs on perennial gramineous weeds. In Inner Mongolia, only one generation of wheat stem maggot larvae damages wheat; after adult emergence, eggs are laid at the base of the leaf surface. In winter wheat areas, 1st- and 2nd-generation larvae damage wheat in April and May, the 3rd generation moves to volunteer wheat seedlings, and the 4th generation moves to autumn seedlings to cause damage. Henan also has two damage peaks per year. After maturity, larvae overwinter at the damage site or on wild hosts. Adults are phototactic and chemotactic; adults mate the same day they emerge, are active among wheat plants during the day, and lay eggs mostly on the wheat stems of the 4th and 5th leaves. Eggs are laid singly; each female can lay more than 20 eggs, with as many as 70-80. Egg laying and larval hatching require relatively high humidity; varieties with soft wheat stems, relatively wide leaves, or few hairs have higher egg-laying rates and suffer heavier damage.

Control methods: (1) Select insect-tolerant or early-maturing varieties suited to the local area according to local conditions. (2) Strengthen cultivation management by sowing early at the proper time and planting at a reasonable density. Strengthen water and fertilizer management to promote uniform wheat growth. Accelerating early wheat growth and development is the fundamental measure to control this insect. (3) Strengthen forecasting and prediction of wheat stem maggot. In winter wheat areas, begin insect surveys in mid to late March, and in spring wheat areas in mid-May. Every 2-3 days, around 10 o'clock, sweep the net 200 times at the top of wheat seedlings. When 2-3 insects are found in 200 net sweeps, about 15 days later will be the peak emergence period of overwintering-generation adults, which is the first suitable period for chemical control. In winter wheat areas, control is needed when the average is 25 insects per 100 net sweeps. (4) When wheat stem maggot adults have reached the control threshold, immediately spray 2.5% trichlorfon powder or 1.5% dimethoate powder or 1% 1605 powder, 1.5 kg per 667 sq m. (5) If wheat stem maggots have already laid a large number of eggs, promptly spray 36% ketenpyrafen-maggot emulsifiable concentrate at 1000-1500 times dilution, or 50% 1605 emulsifiable concentrate at 4000 times dilution, or a 1:1 mixture of 80% dichlorvos emulsifiable concentrate and 40% dimethoate emulsifiable concentrate diluted with water to 1000 times, or 10% Dagongchen wettable powder at 3000 times dilution, or 25% metolcarb wettable powder at 600 times dilution, spraying 50-75 L of the prepared solution per 667 sq m to control the eggs before hatching.