Polychagotarsonemus latus Banks, commonly known as Hemitarsonemus latus Banks, is also referred to as the side-to-multi-food quail line, tea semi-line larvae, and tea leaf mites. It belongs to the class Arachnida, order Tetranychida, and family Tetranychidae. This pest is highly polyphagous, meaning it can feed on a wide range of host plants, making it a significant threat to various crops, especially tea plants.
The damage caused by this mite is quite distinctive. Infested leaves develop oily, yellow-brown spots, and their edges curl downward. The leaves often appear upright, while young stems turn brownish. Severely affected plants become stunted, with twigs falling off and creating bald patches. The stalks and fruit tips turn yellow-brown, lose their shine, and the fruits stop growing, becoming hard and unviable.
In terms of morphology, the female mite measures approximately 0.21 mm in length, has an oval shape, and ranges from pale yellow to orange-yellow. It is translucent, with five pairs of short legs and four pairs of slender ones. The male is smaller, about 0.18 mm long, with a hexagonal body that tapers at the end. It also has a pale yellow to orange-yellow color and is translucent. The eggs are elliptical, around 0.1 mm long, colorless and transparent, with 5–6 rows of white nodules on the surface. Nymphs are elliptical, pale green, and have three clearly divided abdominal segments. Their ends are tapered, with one pair of bristles and three pairs of legs. Some nymphs remain stationary, enclosed in their old skins.
In terms of life habits, this mite completes one generation within 7–10 days at temperatures between 20–30°C. In tropical and greenhouse environments, it can occur year-round, although its reproductive activity decreases in winter. The species is primarily bisexual, but parthenogenesis can also occur. However, unhatched eggs tend to be all male, with low hatching rates. Eggs are usually laid sparsely on the back of young leaves and in the depressions of fruits. Both adult and nymph stages are tender, preferring the upper surfaces of young leaves, tender stems, flowers, and young fruits.
The optimal temperature for growth and reproduction is 16–23°C, with relative humidity between 80–90%. High temperatures inhibit their development, and heavy rainfall can significantly reduce their population.
For prevention and control, regular field monitoring is essential. Early detection during the flowering stage of chili plants allows for timely spraying. A spray should be applied every 10–14 days, with three consecutive applications recommended. The focus should be on the upper leaves, particularly the underside of tender leaves, young stems, flower parts, and developing fruits. Available pesticides include 1.8% spinosad (such as avermectin or efford) diluted at 3000 times, with a safety interval of 7–10 days. 20% compound liuyangmycin EC diluted at 1000 times, with a 7-day interval. 57% kete EC diluted at 800 times, 48% lethben EC diluted at 1500 times, and 20% oleolacil WP diluted at 1000 times. These treatments are effective when applied correctly and consistently.
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