Rhizoglyphus echinopus (Fumouze et Robin), commonly known as the bulb mite, belongs to the family Acrididae. This pest becomes particularly active from May to August, causing significant damage in onion fields and is considered a newly emerging threat in agricultural areas.
Bulb mites primarily affect crops such as onions, leeks, lilies, loquats, beets, potatoes, gladiolus, pinellia, and fritillaria. The symptoms of infestation include yellowing leaves, stunted growth, and wilting. The underground stems or bulbs become dark brown and decayed, with the mites spreading through the roots and into the inner tissues, leading to poor plant development. Seedlings are often the first to show signs of damage, with withered leaves, discoloration, and even blueish tissue lesions. In lilies and other bulbous plants, brown spots appear on the bulbs, and above-ground parts may dry out. Some vegetables and flowers may display purple leaves after germination, which then gradually wither. It's important to differentiate this damage from plant diseases.
Morphologically, adult bulb mites are oval-shaped, measuring 0.6–0.9 mm in length, with a milky-white, shiny body and light reddish-brown legs. They have three pairs of legs as larvae, while nymphs and adults have four pairs. The eggs are white and oval, approximately 0.2 mm long.
In terms of life habits, bulb mites feed on the false stems of leeks and garlic, causing rot. Under high humidity and temperatures between 18.3°C and 23.9°C, one generation takes 17–27 days, but at higher temperatures (20–26.7°C), it can complete in just 9–13 days. Mating occurs within 1–3 days, and females lay an average of 195 eggs, with some reaching up to 500. When environmental conditions are unfavorable, they produce smaller, mobile forms. In Japan, there can be over 10 generations per year. These mites prefer sandy soils and can be found in large numbers, with more than 10 individuals per root. They move freely through the soil and thrive in acidic conditions.
The occurrence of bulb mites is influenced by environmental factors and crop management practices. To control them effectively:
1. Deep plowing and proper fertilization during soil preparation are essential. Applying 80–100 kg of slaked lime per acre helps neutralize the soil.
2. Implement crop rotation to avoid continuous planting of the same host crops, such as melons and beans.
3. Expose root crops to sunlight to reduce infestations.
4. During transplanting, use insect-free seedlings and avoid those showing signs of mite infestation. Soak roots in 20% cypermethrin emulsion or 50% fenitrothion EC diluted 2000–3000 times for 5–10 minutes, achieving up to 90% mortality.
5. For chemical control during the adult stage, apply 48% lindane EC, 20% chlorpyrifos EC, 1.8% abamectin EC, or 20% acephate EC diluted 1000–1500 times around the base of green onions. This method has shown control efficacy exceeding 80%.
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