Melon thrips (Thrips palmi) have a wide host range but are best known as pests of cucurbits and solanaceous crops. Vegetables attacked include bean, cabbage, cantaloupe, Chinese cabbage, cowpea, cucumber, eggplant, lettuce, melon, okra, onion, pea, pepper, potato, pumpkin, squash, and watermelon.
Melon thrips cause severe injury to infested plants. Leaves become yellow, white or brown, and then crinkle and die. Heavily infested fields sometimes acquire a bronze color. Damaged terminal growth may be discolored, stunted, and deformed. Feeding usually occurs on foliage, but on pepper, a less suitable host, flowers are preferred to foliage. Because melon thrips prefer foliage, they are less damaging to cucumber fruit than western flower thrips (Frankliniella occidentalis). Nevertheless, cucumber fruits also may be damaged. Scars, deformities, and abortion are reported. In addition to direct injury, melon thrips are capable of transmitting some strains of tomato spotted wilt virus and bud necrosis virus.
Larvae feed in groups, particularly along the leaf midrib and veins, and usually on older leaves. Adults are pale yellow or whitish in color, but with numerous dark setae on the body. A black line, marking the juncture of the wings, runs along the back of the body. The slender fringed wings are pale. Unlike the larvae, adults tend to feed on young growth, and so are found on new leaves.
Survival And Spread
Melon thrips reproduce in any season but are favored by warm weather. In South Florida, they are damaging on both autumn and spring vegetable crops. Eggs are deposited in leaf tissue in a slit cut by the female. The egg is bean-shaped and colorless to pale white. Females may produce up to 200 eggs, but average closer to 50. The larvae resemble the adults but they lack wings and are smaller. There are two instars during the larval period. Larval development time is determined principally by temperature, but host plant quality also has an influence. On completion of the larval stage, the insect descends to the soil or leaf litter where it pupates.
Densities from 1 to 10 per cucumber leaf have been proposed as the threshold for economic damage in some studies. Growers should check older leaves for adults and larvae. It helps to turn the undersurface of the leaf at 45-degree angle toward light to observe glittering feeding damage.
Foliar insecticides are frequently applied for thrips suppression, but at times it is difficult to attain effective suppression. It is usually inadvisable to apply insecticides if predators are present. Use of a non-ionic surfactant with insecticides will help improve control. Radiant (spinetoram, Dow AgroSciences) and Entrust (spinosad, Dow AgroSciences) have given good control and are both relatively easy on beneficial insects. Eggs and pupae are relatively insensitive to insecticide application. Other materials including: Lannate (methomyl, DuPont Crop Protection), Vydate (oxamyl, DuPont Crop Protection), Agrimek (abamectin, Syngenta), Provado (imidacloprid, Bayer CropScience), Trilogy (extract of neem oil, Certis USA), and Requiem (extract of Chenopodium ambrosioides, AgraQuest) should provide control.