Melon thrips

Melon thrips (Thrips palmi) is an insect from the Thrips genus. It is a primary vector of plant viruses. T. palmi can cause damage to a wide range of glasshouse ornamental and vegetable crops, particularly plants in the families Cucurbitaceae and Solanaceae, such as cucumber, aubergine, tomato and sweet pepper.

Symptoms
Adults and nymphs feed by sucking the cell contents from leaves, stems, flowers and the surface of fruits, thereby causing silvery scars, and leaf chlorosis. Plant growth can be deformed and heavily scarred. A severe infestation can kill the entire plant.

Cultural control
Several cultural practices apparently affect melon thrips abundance, but few have been evaluated in the context of North American agriculture. Physical barriers such as fine mesh and row cover material can be used to restrict entry by thrips into greenhouses, and to reduce the rate of thrips settling on plants in the field.

Organic mulch is thought to interfere with the colonization of crops by winged thrips. Plastic mulch also is reported to limit population growth, but it is uncertain whether this is due to reduced rates of invasion or denial of suitable pupation sites.

Heavy rainfall is thought to decrease thrips numbers. However, there seems to be no evidence that overhead irrigation is an important factor in survival.

Resistance
Susceptibility to injury varied among pepper cultivars. Although sweet and jalapeno types were sensitive to foliar injury, cubanelle and cayenne types produced acceptable size and quality fruit. This is the reverse of injury susceptibility to western flower thrips, so in areas with mixed thrips populations growers cannot rely solely on plant selection to avoid damage.

Biological control
The predatory mite Neoseiulus cucumeris has been investigated for suppression of melon thrips. The mite density is correlated with thrips density, but within-plant distribution differs among the two species, suggesting that although the mites may increase in numerical abundance they are unlikely to drive the thrips to extinction.

Chemical control
Foliar insecticides are frequently applied for thrips suppression, but at times it has been difficult to attain effective suppression. Various foliar and drench treatments, alone or combined with oil, have achieved some success though it is usually inadvisable to apply insecticides if predators are present. The eggs, which occur in the foliar tissue, and the pupae, which reside in the soil, are relatively insensitive to insecticide application.