Melon thrips (Thrips palmi) has spread from Southeast Asia to many tropical regions of the world. In the U.S., they were first detected in Hawaii in 1982 and reached Florida in 1990. In Florida, they are only a pest in the southern part of the state.
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, or deformed.
Because melon thrips prefer foliage, they are less damaging to cucumber fruit than western flower thrips (Frankliniella occidentalis). Nevertheless, fruit damage has been 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 are found on new leaves.
Careful examination is required to distinguish melon thrips from other common thrips. The Frankliniella species are easily separated because their antennae consist of eight segments, whereas in other thrips species there are seven segments.
Survival and Spread
Melon thrips reproduce in any season but favor warm weather. In South Florida, they damage both spring and fall crops. Eggs are deposited in leaf tissue, in a slit cut by the female. The egg is bean-shaped and colorless to pale white in color. Females may produce up to 200 eggs, but average closer to 50.
The larvae resemble the adults, but they are smaller and lack wings. There are two instars during the larval period.
On completion of the larval stage, the insect descends to the soil or leaf litter where it pupates.
In some studies, densities from one to 10 per cucumber leaf have been proposed as the threshold for economic damage. Growers should check older leaves for adults and larvae.
Natural enemies, particularly predators like the minute pirate bug, are important in the natural control of melon thrips.
Foliar insecticides are frequently applied for thrips suppression, but at times it is difficult to attain effective suppression. Growers should avoid broad-spectrum insecticides to preserve predators. Use of a non-ionic surfactant will help improve control.
Growers should be sure to rotate insecticides with different modes of action to avoid developing resistance.
Consult UF/IFAS recommendations for currently labeled insecticides for melon thrips control in Florida.