A Complete Guide to Onion Thrips Damage and Control Methods

I. Distribution and Damage

Onion thrips, also known as tobacco thrips, cotton thrips, etc., belongs to the order Thysanoptera, family Thripidae. It mainly damages onions, scallions, garlic, Chinese chives, cucurbits, eggplant, Chinese cabbage, potatoes, and so on.

Both adults and nymphs use their piercing-sucking mouthparts to suck the sap from tender tips and heart leaves of plants. Damaged scallions develop many fine, elongated grayish-white spots, the leaf tips turn yellow and dry up, and in severe cases the leaves become twisted and withered.

II. Morphological Characteristics

Adult. Body length 1-1.3 mm, light yellow to dark brown, etc. Wings slender and transparent, with many fine long hairs densely covering the margins.

Egg. Length 0.2 mm, kidney-shaped, gradually becoming oval.

Nymph. Body similar to the adult; first instar body length 0.3-0.6 mm. Fourth instar nymph (pseudopupa) body length 1.2-1.6 mm. Antennae tilted toward the dorsal side of the head and thorax.

III. Life Habits

Widely distributed in China; in the north it produces 6-10 generations per year, mainly overwintering as adults and nymphs in the leaf sheaths of unharvested scallions, onions, and garlic, with a few overwintering as pseudopupae in crop residues, weeds, and soil. In South China it can occur and cause damage year-round. In the following spring, adults and nymphs begin to become active and cause damage. Adults are lively, good at flying, and can migrate and spread by wind, but they fear light; during the day they often stay on the underside of leaves or at the leaf veins and leaf axils, and only come to the leaf surface to feed in the early morning, evening, on cloudy days, and at night. They enter the peak damage period in May-June. Eggs are laid singly in stem and leaf tissues; they can reproduce by parthenogenesis, with males appearing only in autumn. Females insert their ovipositors into scallion tissues to lay eggs, and in the later stage of egg development small bumps can be seen on the leaf surface. Newly hatched nymphs have the habit of congregating to cause damage, and disperse as they grow slightly larger. The 1st and 2nd instars are the damaging stage; late 2nd instars enter the soil and pass through the 3rd and 4th instar stages, finally emerging as adults. This pest prefers warm and relatively dry environmental conditions; in the north during winter and early spring it also damages greenhouse cucumbers and other vegetables.

IV. Control Methods

1. Agricultural control. Clean up the field in early spring, and collect and destroy dead branches, fallen leaves, and weeds together to reduce overwintering pest sources. Proper frequent weeding and irrigation can reduce or alleviate the damage.

2. Chemical control. Take advantage of the favorable timing when 1st and 2nd instar nymphs are causing damage to apply pesticides. Options include 40% dimethoate emulsifiable concentrate, 50% dichlorvos emulsifiable concentrate, and 50% cartap soluble powder, each at 1000-fold dilution; or 40% diazinon emulsifiable concentrate and 50% malathion emulsifiable concentrate, each at 1000-2000-fold dilution; or 10% cypermethrin emulsifiable concentrate at 1500-3000-fold dilution; or a 1:1 mixture of 3% malathion powder and 2% dimethoate powder, applied at 1.5-2 kg per 667 sq m, sprayed in the early morning before the dew has dried. Although the above pesticides are highly effective and low in toxicity, use should still be stopped 7-10 days before harvest. In addition, spraying with tobacco-lime water (ratio 1:0.5:50) also has a good control effect.