Cotton seedling thrips (Onion thrips, cotton thrips)
Onion thrips feed on many cultivated crops as well as uncultivated plants in at least 25 families. Principal crop hosts include beans, broccoli, cabbage, carnation, carrot, cauliflower, Chinese broccoli, cotton, cucumber, garlic, head cabbage, leek, melon, onion, orchids, papaya, peas, pineapple, rose, squash, tobacco, tomato, and turnip.
Adults are 1/25 inch long. Their body color ranges from pale yellow to dark brown; wings are unbanded and dirty gray. In Hawaii, this species has a darker form during the rainy season. Males are wingless and exceedingly rare. Females live for about two to three weeks and each can lay about 80 eggs.
Larvae and adults are found mainly in the narrow space between the tubular leaves of onions, in flowers and on the underside of foliage of certain other plants. Thrips feed by piercing individual cells and sucking the contents. These cells lose their normal color, and when many adjacent cells are damaged, the tissue appears as whitish spots or silvery spots or streaks. In advanced injury the leaves take on a blasted appearance. As is common with many thrips species, onion thrips deposit small dark specks of excrement on the surface of tissue where they feed. Substantial damage can be done to young plants especially to varieties grown in seed beds.
Besides direct damage caused by feeding of larvae and adults, this pest is also important as a vector of tomato spotted wilt virus and has been involved in transmitting the disease in pineapple, tomatoes, and certain other crops.