|Crop Knowledge Master|
Thrips palmi (Karny)
Jayma L. Martin, Educational Specialist
Ronald F.L. Mau, Extension Entomologist
Department of Entomology
Updated by: J.M. Diez April 2007
Melon thrips feed on many hosts, included are over 50 plant species representing over 20 taxonomic families (Wang and Chu, 1986). Crop plants reported to have been damaged, often severely, are: Solanceae: eggplant, pepper, potato, tobacco, ground cherry; Cucurbitaceae: bittermelon, cucumber, watermelon, muskmelon, cantaloupe, pumpkin, squash, zucchini; Leguminosae: kidney bean, broad bean, cowpea, green bean, soybean; Misc: amaranth spinach, Chinese wax gourd, Chinese spinach, chrysanthemum, cotton, cyclamen, dahlia, edible gourds, hyotan, morning glory, orchid, plumeria, sesame, sweet potato and togan. In addition, various weeds are also attacked. Melon thrips are a primary foliar pest on watermelon, eggplant, cucumber, and peppers in Hawaii . It is a pest of quarantine importance to dendrobium orchids.
Melon thrips have a world wide distribution throughout the Pacific. They are present in Bangladesh, China, Guam, Hawaii, Hong Kong, India, Indonesia, Japan, Malaya, New Caledonia, Pakistan, Philippines, Samoa, Singapore, Sudan, Taiwan, Thailand, and Wallis. In 1982 and 1983, severe infestations of melon thrips were discovered in Hawaii on cucurbits, eggplant, pepper, and amaranth spinach (Nakahara, 1984). The pest is also found in Florida, Puerto Rico, and on many Caribbean islands.
Melon thrips quickly build up heavy infestations causing severe injury. Both larvae and adults feed gregariously on leaves (first along midribs and veins), stems (particularly at or near the growing tips), flowers (among the petals and developing ovary) and fruits (under the calex or sepals). Scarring and deformities can result from extensive feeding.
Thrips are frequently found in pockets, cracks, or crevices on host material. Look for silvery feeding scars on leaf surfaces of host plants, especially alongside the midrib and veins. Heavily infested plants are characterized by silvered or bronzed appearance of leaves, stunted leaves and terminals, and scarred and deformed fruits. Individuals may be found on all parts of many kinds of plants during the outbreak stage.
Life stages of the melon thrips are the egg, two larval instars, two pupal instars, and the adult. The adult, egg, and two larval stages are found on the host. Pupae occur in the soil or among leaf litter. Duration of life cycle (egg to adult) for the melon thrips is 11 days at 86 degrees and 26 days at 62.6 degrees Fahrenheit.
The kidney shaped yellowish-white eggs are small, measuring approximately 1/100 inch in length and less than 1/100 inch in diameter. They are generally deposited into the leaves, flowers, and fruit. Eggs hatch in 3 days.
Melon thrips have two active, feeding larval stages. Larvae are pale, transparent yellow in color, and similar in appearance except for size. The first stage is approximately 1/50 inch in length and the second about 1/35 inch. They are similar to the adults in body form, but lack wing buds or wings and have smaller eyes. When the second stage larvae are fully fed, about 3 days after hatching, they crawl to the ground. They remain there for 1 to 2 days before becoming pupae.
The pupal stage in thrips is a resting period in the developing insects before becoming adults. There is no feeding during this stage. This period is divided into two stages, the prepupa and the pupa. Prepupae have free moving, backwardly flexed antennae and two short wing buds, or incompletely developed wings. This stage will last a day. After a molt, the insects become pupae. The pupae differ from the prepupae in having antennae fused to the body and considerably longer wing buds. If their containing cell breaks, these stages are able to walk slowly and clumsily. Their poor mobility and lack of feeding during this stage make them vulnerable to desiccation in drought conditions. The entire pupal period lasts about 3 days.
Under field conditions it is difficult to identify thrips to a species level. It is usually necessary to use a microscope. To the naked eye, adult melon thrips are yellow in color and measure approximately 1/25 inch long.
In examination by microscope, the major diagnostic characters for the melon thrips are: 1) clear yellow body without any grayish or brownish blotch, but with blackish and thick body hairs (setae); 2) interocellar setae outside ocellar triangle; 3) metascutum striates in mesial area and posteriorly converges mesad; 4) abdominal tergite II with 4 lateral setae; 5) abdominal tergites without accessory setae; 6) abdominal VIII with comb complete in both sexes; 7) male sternites III-VII each with transverse globular area. Antennal colors are variable and not reliable for diagnosis.
The melon thrips is a bisexual species. Females reproduce with or without copulation. Unmated females produce progeny by parthenogenesis. Only males are produced by unmated females. Mated females produce predominately females. They may lay over 200 eggs in the course of their 2 month life span.
Adults are good flyers, but their small size makes their dispersal susceptible to wind and weather. Their activity peaks during hot weather when updrafts may carry them great distances.
To date, there are few cultural control methods known that are highly effective in controlling melon thrips. Mulching and the use of reflective material on the field has given some control while plants are small. No host plant resistance has been recorded.
Several natural enemies have been reported for melon thrips. A flower bug of genus Orius was observed by Johnson (1986) preying on melon thrips on watermelon in Hawaii. Other flower bugs have been observed preying on T. palmi in India (Kumar and Ananthakrishnan, 1984) and China (Wei et al., 1984). These bugs are general feeders. Hamasaki observed two species of mite predators.
The melon thrips is resistant to most insecticides. As a result, eggplant growers in Hawaii have reduced their pesticide applications to conserve natural enemies. Growers on Oahu and Maui have successfully used this strategy. Methiocarb was found to be the most effective on cucurbits in New Caledonia but the insecticide is not registered for use on food crops in the U.S. Oxamyl was once effective, but its current usefulness is doubtful. Single treatments of oxamyl applied to watermelon reduced active immature stages somewhat, but did not affect populations. Two treatments, applied 3 days apart, however, had significantly better results (Johnson, 1986). Tolerance to organophosphates was reported in Japan (Suzuki, 1982).
There is no listing for Oxamyl as of April 2007.
Gusukuma-Minuto, L. R. 1990. Host Preference Evaluation of the Melon Thrips, Thrips palmi Karny (Thysanoptera: Thripidae). MS Thesis, University of Hawaii, Department of Entomology.
Hamasaki, R. T. 1987. Impact of Insecticides and a Predatory Mite on Melon Thrips, Thrips palmi Karny. MS Thesis, University of Hawaii, Department of Entomology.
Johnson, M. W. 1986. Population Trends of a Newly Introduced Species, Thrips palmi (Thysanoptera: Thripidae), on Commercial Watermelon Plantings in Hawaii. J. Econ. Ent. 79(3): 718-720.
Johnson, M. W., R. F. L. Mau, A. P. Martinez and S. Fukuda. 1989. Foliar Pests of Watermelon in Hawaii. Tropical Pest Management. 35(1): 90-96.
Kumar, N. S. and T. N. Ananthakrishnan. 1984. Predator-Thrips Interactions with Reference to Orius maxidentex Ghauri and Carayonocoris indicus Muraleedharan (Anthocoridae: Hemiptera). Proc. Indian Natn. Sci. Acad. B50(2): 139-145.
Nakahara, L. M. 1984. New State record: Thrips palmi Karny. Hawaii Pest Report. Hawaii Dept. Agr. 4(1): 1-5.
Rosenheim, J. A., S.C. Welter, M. W. Johnson, R. F. L. Mau and L. R. Gusukuma-Minuto. 1990. Direct Feeding Damage on Cucumber by Mixed-Species Infestations of Thrips palmi and Frankliniella occidentalis (Thysanoptera: Thripidae). J. Econ. Ent. 83(4): 1519-1525.
Sakimura, K., L. M. Nakahara, and H. A. Denmark. 1986. A Thrips, Thrips palmi Karny (Thysanoptera: Thripidae). Fla. Dept. Agric. & Consumer Serv. Entomology Circular No. 280.
Suzuki, H., S. Tamaki and A. Miyahara. 1982. Physical Control of Thrips palmi Karny. Proc. Assoc. Pl. Prot. Kyushu. 28: 135-139 (in Japanese).
Wang, C. L. and Y. I. Chu. 1986. Review of the Southern Thrips, Thrips palmi Karny. Chinese J. Entomol. 6: 133-143 (in Chinese).
Waterhouse, D. F. 1987. Chapter 11: Thrips palmi Karny Thysanoptera: Thripidae, pp. 90-94. In Biological Control: Pacific Prospects (Ed. D.F. Waterhouse and K.R. Norris). Inkata Press, Melbourne, Australia. 454 pages.
Wei, C. L., Z. J. Peng, G. Q. Yang, Y. Cao, B. Z. Huang and X. Chen. 1984. On the flower bug, Orius similis Zheng. Natural Enemies of Insects. 6(1): 32-40.