What are the dangers of wheat aphids and how to prevent and control wheat aphids?

Wheat aphids are one of the important pests of wheat in my country. They occur to varying degrees every year, but the control effects in recent years are poor. Adult aphids and nymphs of wheat aphids suck the juice from the leaves, stems and ears of wheat plants, causing yellow spots or all yellowing on the leaves, stagnant growth, reduced tillers, and grains that are thin or unable to bear fruit. Wheat aphids not only suck plant sap and affect crop development, but can also spread a variety of viral diseases, which can cause serious losses in wheat production. This article introduces in detail the morphological characteristics, occurrence patterns, harm and prevention methods of wheat aphids for your reference.

1. Morphological characteristics of wheat aphids

1.1 The wingless parthenogenetic aphid of Wheat Aphids is 3.1mm long, 1.4mm wide, long and nine-shaped, grass green to Orange-red, sometimes red or brown on the head, with inconspicuous gray-green to gray-black spots on both sides of the abdomen. The tentacles are black, and there are 8 to 12 sensory circles lined up in the third segment. Sections 6-8 of the abdomen and ventral surface were covered with transverse reticulate patterns, with no bordering tumors. The beak is thick, black, and longer than the base of the midfoot. The abdominal tube is long, cylindrical, black, 1/4 of the body length, and has more than ten rows of reticulated patterns at the end. The winged parthenogenetic aphids are 3.0mm long, oval, and green. The beak does not reach the base of the midfoot. The abdominal tube is long cylindrical, black, with 15 to 16 rows of transverse reticulation at the end, and the tail piece is long and conical with 8 to 9 hairs. If the aphid body is green, sometimes pink, the compound eyes are red, and the body is generally short.

1.2 The body of aphids is round, 2.0mm long and 1.0mm wide. Light green, dark green on dorsal midline. The antennae have 6 segments and are black, but the base half of the 3rd segment and the 1st and 2nd segments are light colored, reaching 2/3 of the body length. The beak is light in color, but the third segment and the terminal segment are gray-black, longer than the base segment of the midfoot, and the terminal segment is thick and short. The abdominal tube is long cylindrical, light green, with a black top. The middle frontal tumor is slightly raised, and the frontal tumor is taller than the middle frontal tumor. The middle thorax and abdomen have short handles. Winged parthenogenetic aphids: The body is oval, 1.8mm long and 0.73mm wide. The head and chest are black, and the abdomen is light in color. The tentacles are black and have 6 segments, and the total length exceeds 1/2 of its body length. The third segment of the tentacles has 4-10 small circular secondary sensory circles arranged in a row. Forewing midrib bifurcated. Other characteristics are similar to the wingless type.

1.3 The wingless parthenogenetic aphid of the cereal constrictor aphid is a wide oval body, 1.9 millimeter long, 1.1 millimeter wide, olive green to black green, with yellow-green streaks embedded in it. It is often covered by Thin wax powder. The antennae have 6 segments and are black, but the bases of the 1st, 2nd and 3rd segments are light colored, and the length exceeds 1/2 of the body length. The middle chest and abdomen are branched and without a handle. The midfrontal tumor is raised. The beak is thick, longer than the base of the midfoot, and the length is twice as long as the width. The abdominal tube is gray-black, with a black top, long cylindrical shape, and an obvious edge. There are often light brown or rust-colored markings around the base of the abdominal tube. The tail piece and tail plate are grayish brown. The winged parthenogenetic aphid is elongated, with a body length of 2.1 millimeter and a width of 1.1 millimeter. The head and chest are black, and the abdomen is dark green with black markings. The 3rd segment of the tentacles has 19 to 28 round secondary sensory circles, and the 4th segment has 2 to 7 circles. There are large green spots on the 2nd to 4th segments of the abdomen. The spots are large behind the abdominal tube and extend forward around the abdominal tube. Sections 7 and 8 have a middle transverse belt on the abdomen and back. Abdominal tube black. Other characteristics are similar to the wingless type. If the aphid body is lavender, with white powder on the cover, compound eyes are brown, and the antennae and legs are light in color.

2. The occurrence pattern of wheat aphids

Wheat aphids can produce more than 10 to 30 generations in one year. In the area south of the Yellow River, the wheat aphid produces aphids and nymphs as wingless embryos and overwinters around the rhizosphere of the host or under the soil. In the south of the Yangtze River, there is no obvious dormancy phenomenon. In places below -10~(2, it cannot survive in winter. Overwintering. As the temperature rises every spring, the overwintering long-tube aphids produce a large number of winged aphids, which migrate to the northern winter wheat areas with the air flow to reproduce and cause damage. ① The wheat aphids lay their eggs on dead leaves, soil cracks and weeds of wheat seedlings in the north. They overwinter on top or under soil clods. In the south of the Huaihe River, adult aphids and nymphs overwinter in wheat seedlings and soil cracks without obvious dormancy. They can still crawl to the leaves to feed when the weather is warm. In the north of the Yangtze River, the eggs overwinter in the bark cracks and bud axils of apples, peaches, etc. They seriously damage wheat in mid-to-early May. After the wheat is harvested, they move to corn and sorghum in large numbers and cause damage. ③ Wheat tube aphids. As the plant grows, the damage spreads to the upper leaves, and it prefers to suck on the young ears, so it is also called "ear aphid". It is distributed in the lower part and damages the back side of the leaves. The number of cereal aphids increases significantly in the late milk-ripening stage. Grain aphid prefers a moist environment and mostly damages the underside of wheat leaves, even on the leaf sheaths at the base of wheat stems.

The occurrence of wheat aphids is closely related to temperature and humidity. When the temperature is 6°C or higher than 28°C, the population of wheat aphids decreases significantly. When the humidity is lower than 40%, the occurrence of wheat aphids is also significantly suppressed.

3. Wheat aphids are the main species. Harm

3.1 Nutritional sucking Wheat aphids harm wheat by sucking the sap from stems, leaves and young ears of wheat plants as adults and nymphs. Injury in the early stage of wheat seedlings can cause the leaves to turn yellow, affect growth, and even wither and die; Damage during the booting stage affects heading; in the later stages, small yellow spots appear on the damaged parts, the wheat leaves gradually turn yellow, and the wheat grains are not full. In severe cases, the wheat ears become white, unable to bear fruit, or even the whole plant dies, seriously affecting the yield.

< p>3.2 Impact on photosynthesis When wheat aphids occur in large numbers, the honeydew excreted by aphids is smeared on wheat leaves and young ears, seriously affecting photosynthesis and causing wheat yield reduction.

3.3 Virus-transmitting wheat aphids can also spread wheat yellow dwarf disease, causing wheat leaves to turn yellow and plants to become dwarfed, affecting yields and causing greater losses than sucking nutrients.

4. Wheat aphid control methods

4.1 Agricultural control: Reasonably adjust the crop layout. For example, do not plant winter wheat in spring wheat areas, and reduce the sorghum planting area in winter wheat areas. Adjust the sowing time to avoid the peak period of aphid occurrence at the ear stage, so that the wheat heading maturity period can be advanced or delayed accordingly to reduce aphid damage. Choose early-maturing varieties. Since early-maturing varieties grow and develop earlier, when the temperature for wheat aphids arrives, the wheat growth period is already in the later stages, which can avoid or reduce aphid damage.

Timely shallow plowing to eliminate stubble after wheat harvest, combined with deep plowing, can eliminate self-growing wheat seedlings and various grassy weeds in the wheat field, and control the number of oversummer aphids. Where conditions permit, winter irrigation and early spring harrowing can be implemented.

4.2 Protection and Utilization of Natural Enemies There are many natural enemies of aphids. Among them, the predatory natural enemies that have strong control over wheat aphids include various ladybirds, lacewings, hoverflies, and flower bugs; there are many parasitic natural enemies. Aphid braconid wasp. These natural enemies are abundant in wheat fields. When the ratio of the number of natural enemies to the number of aphids reaches more than 1:150, the natural enemies can control the wheat aphids below the control indicators without using pesticides. Therefore, wheat fields should pay attention to the scientific use of medication and choose selective agents that are safe against natural enemies.

4.3 Chemical control Spring is the season suitable for the growth and damage of aphids, and the main species are wheat aphids. Temperature and humidity play a leading role in the growth and decline of wheat aphids. Generally speaking, the temperature between 15 and 25°C and the relative humidity between 40% and 80% are the conditions for the occurrence of wheat aphids. From the perspective of wheat growth and development period, the number of aphids increases slowly before heading, rises sharply after heading, and reaches the highest peak from the filling period to the milky stage. During the filling period, aphid damage causes the most serious losses to wheat yield. Therefore, wheat aphids should be prevented and controlled in time during the late flowering and early grain-filling stages of wheat. The pharmaceuticals can be 10% imidacloprid wettable powder 2000 times liquid, 25% cyclosulfide EC 1000 times liquid, 3% acetamiprid EC 1500 times liquid, 2.5% Baode EC 2500 times liquid, 5% high-efficiency Dagongchenke Wet powder 1000 times liquid and 50% pirimicarb wettable powder 4000 times liquid etc. Long-term single use of pesticides can easily cause wheat aphids to become resistant to pesticides. Therefore, it is necessary to arrange and rotate medications reasonably.

5. Misunderstandings in wheat aphid control

5.1 Delaying the best control period

At present, the control of wheat aphids is too early or too late. Applying pesticides as soon as an insect appears, the number of sprays increases accordingly, resulting in high control costs and increased aphid resistance, further increasing the difficulty of control. If the control is too late, aphids have already caused certain damage to wheat. Aphid density is too high. If pesticides cannot be applied evenly, the damage of aphids cannot be effectively controlled.

5.2 Improper selection of pesticides

Most farmers lack pertinence when choosing pesticides and mistakenly believe that highly toxic pesticides have relatively better insecticidal effects. Highly toxic and toxic pesticides are generally broad-spectrum pesticides. while effectively controlling target pests. It will also harm natural enemies and some beneficial organisms such as bees, thereby destroying the balance of the entire farmland ecosystem and causing pollution to humans, animals, water bodies, and the ecological environment. At the same time, highly toxic pesticides have a short duration of effect and high residues. When applied close to the harvest period, pesticide residues in grains exceed standards, which is not conducive to people's healthy life. In addition, most farmers lack some conventional knowledge to distinguish between real and fake pesticides, such as the three pesticide certificates. If fake pesticides are accidentally used, it will not only increase the cost of prevention and control, but also fail to achieve the purpose of preventing diseases and pests, causing great harm to production.

5.3 Unreasonable pesticide application techniques

Some farmers abuse pesticides, use a relatively single variety, and apply pesticides frequently, resulting in a significant increase in the insect's resistance to pesticides. Farmers have no choice but to further increase the amount and frequency of pesticide application, which will further increase the resistance of the insect and increase the cost of control. Secondly, the amount of water used during pesticide application is generally less and the pesticide is applied unevenly. Especially in the middle and late stages of wheat, the field density is high, and it is difficult to reach aphids on the backs of leaves and stems. When the weather is suitable, it is easy for aphids to flourish again. Therefore, spraying is often required 2 to 3 times during the growth period of wheat. Difficulty and high cost of control are the biggest problems in wheat aphid control.