Melon thrips

Thrips palmi Karny

Thysanoptera: Thripidae

Melon thrips is a major pest, originated from South East Asia, which has spread from there and gained a foothold in many tropical and subtropical regions of the world.

Host plants and damage

Melon thrips is a major pest of cucurbits and solanaceous plants in many tropical regions of the world. They attack over 50 plant species representing over 20 taxonomic families. Main host crops are Cucumis sativus (cucumber), Cucumis melo (melon), Piper nigrum (pepper), Cucurbita pepo (squash), Helianthus annuus (sunflower), and Vigna unguiculata (cowpea). Melon thrips population build up quickly.

Adults and nymphs feed by sucking cell contents from leaves, stems, flowers, and fruit surfaces. Melon thrip feeding shows the typical damage caused by thrips. Leaves turn silvery or bronze, sometimes yellow. If infestation is severe terminal shoots become stunted and fruits scarred and deformed.

Melon thrips is a vector for tomato spotted wilt virus (Tospoviruses). This virus is capable of infecting a range of plants, including cucurbits.

Morphology & biology

Eggs are kidney shaped, yellowish-white and are deposited into leaves, flowers, and fruits. They hatch after 2-4 days.

Melon thrips have two active feeding larval stages. They are transparent to yellow in color and look similar to the adults except for the wings. The second larval stage moves when fully fed to the ground for pupation.

Pupation takes place in the soil. Prepupal stage lasts one day before molting into the final pupa. Pupae are dark orange in color but remain unseen for several months in the soil.

Adult melon thrips emerge from the pupae and move to leaves and flowers of host plants. They make an incision in the green leaf tissue with their ovipositor and lay their eggs. Each female can deposit up to 200 eggs in their lifetime.

Adults have slender wings, which are fringed with long hairs. Females are pale yellow in color, have brown hairs on the body and antennae with seven segments. Male adults are similar to females but smaller.

Adults are good fliers and can be dispersed by wind and weather over long distances.

Species can be distinguished from other thrips species under the microscope. Characteristics for melon thrips are: 1) clear yellowish body with thick and black body hairs (setae), 2) abdominal tergites without setae, 3) abdominal VIII with comb complete in both sexes. The antennal colors are variable and can not be used for species identification.

A complete generation can be completed in about 12 to 20 days, depending on the temperature.

Monitoring

All thrips are small and very difficult to detect. Adhesive traps, favorable in white color, or water pan traps in the field can be used for monitoring melon thrip populations.

Check plants regularly for signs of damage.

Pest management

Rainfall is known to effect negatively Thrips populations.

Biological control

There are many natural enemies of melon thrips which can contribute to the control of thips.

Most important predators are Anthocorid bugs and ladybird beetles. Seven Anthocorid bug species including Orius similes and O. tantillus have been described in Asia.

The parasitoid Ceranisus menes Walker (Hymenoptera: Eulophidae) shows particular benefit in Asia.

There are several fungi affecting melon thrips, including Beauveria bassiana, Neozygites parvispora, and Verticillium lecanii.

Cultural control

Thrips populations were smaller in Trinidad when weeds were frequently removed. Some weeds can serve as alternative hosts.

In Japan and South-East Asia are resistant eggplant varieties available.

Chemical Control

Melon thrips became resistant to many organophosphates and other active ingredients in synthetic insecticides. As a result in eggplant fields in Guadeloupe melon thrips populations were much higher in diazinon- and profenofos-treated plots than in untreated.

Effective foliar insecticides can be applied alone or with oil to suppress thrip populations.