|Crop Knowledge Master|
Thrips tabaci (Linderman)
Ronald F.L. Mau, Extension Entomologist
Jayma L. Martin Kessing, Educaitonal Specialist
Department of Entomology
Onion thrips feed on many cultivated crops as well as uncultivated plants in at least 25 families. Principal crop hosts include beans, broccoli, cabbage, carnation, carrot, cauliflower, Chinese broccoli, cotton, cucumber, garlic, head cabbage, leek, melon, onion, orchids, papaya, peas, pineapple, rose, squash, tobacco, tomato, and turnip.
Believed to have originated in the Mediterranean region, the onion thrips is cosmopolitan in distribution throughout most of the world. This thrips was first found in Hawaii in 1915 and is now present on all islands.
Larvae and adults are found mainly in the narrow space between the tubular leaves of onions, in flowers and on the underside of foliage of certain other plants. Thrips feed by piercing individual cells and sucking the contents. These cells lose their normal color, and when many adjacent cells are damaged, the tissue appears as whitish spots or silvery spots or streaks. In advanced injury the leaves take on a blasted appearance. As is common with many thrips species, onion thrips deposit small dark specks of excrement on the surface of tissue where they feed. Substantial damage can be done to young plants especially to varieties grown in seed beds.
Besides direct damage caused by feeding of larvae and adults, this pest is also important as a vector of tomato spotted wilt virus and has been involved in transmitting the disease in pineapple, tomatoes, and certain other crops.
Stages in the developmental cycle are the egg, first larval stage, second larval stage, prepupa, pupa, and adult. Because of their small size, this pest species like other thrips cannot readily be identified to species even with a hand lens. Adult specimens are usually needed to make species identifications under high microscope magnification.
The entire life cycle (egg to adult) requires about 19 days. Large populations are able to develop quickly under Hawaiian weather conditions where there are many overlapping generations throughout the year.
Reproduction of this species in Hawaii is mostly through a process called parthenogenesis in which females are able to reproduce without mating. As a result, populations consist of females at a ratio of 1 male per 1000 females (Sakimura, 1932).
Females have a saw-like structure that helps to make an incision in plant tissue for egg laying. Eggs are placed singly just under the epidermis of succulent leaf, flower, stem or bulb tissue. Eggs are elliptical, approximately 1/125 inch in length. They are whitish at deposition and change to an orange tint as development continues. Hatching occurs in 4-5 days in Hawaii.
Larvae are whitish to yellowish. There are two larval stages and besides the adults they are the only damaging stages. Larval development is completed in about 9 days.
There are two non- feeding stages called the prepupa and pupa. They do not feed and occur primarily in the soil. Combined prepupal and pupal development is completed in 4-7 days.
Adults are 1/25 inch long. Their body color ranges from pale yellow to dark brown; wings are unbanded and dirty gray. In Hawaii, this species has a darker form during the rainy season. Males are wingless and exceedingly rare. Females live for about two to three weeks and each can lay about 80 eggs.
Several natural enemies have been introduced to Hawaii in an attempt to help control this pest. However, only the parasite, Ceranisus menes, has become established. Unfortunately the impact of this parasite is not considered great.
Cultural control practices can help reduce onion thrips infestations. Destruction of piles of cull onions between crops reduces the abundance of this pest along with other sanitation techniques such as removing weeds in the field and outlying areas. These practices help eliminate alternative hosts on the onion thrips between crops. Crop rotations to prevent the successive plantings of several onion crops and interplanting with non-host crops can also be effective in deterring large populations.
While the onion thrips can be readily killed by many insecticides, they are often difficult to control because of their small size and cryptic habits. Insecticidal control of this pest depends on the choice of an effective chemical and adequate spray coverage on parts of the plant where the thrips inhabit. For example, control of this pest on onions is exceedingly difficult because of the shape of onion leaves. Many larvae and thrips are found in the leaf axils which often do not receive insecticide deposits.
Thrips are shallow feeders that feed primarily on surface tissue. Contact-residual insecticides are more effective. Systemic insecticides which transport through the plants vascular tissues are not as likely to be effective if they are not applied in a manner like other contact insecticides.
Another important aspect of insecticidal control is spray intervals. Since eggs, prepupae, and pupae are not easily killed by insecticidal sprays, the time required for egg incubation and larval development must be considered. In order to control high population densities of this pest during warm, dry periods, repeated applications at 7-10 day intervals are required.
Clausen, C. P. (Ed.) 1978. Onion Thrips, (Thrips tabaci Lindeman). pp. 20-21. In USDA Agriculture Handbook #480: Introduced Parasites and Predators of Arthropod Pests and Weeds: A World View. 545 pages.
Lockwood, S. 1956. Onion Thrips, Thrips tabaci. California Department of Agriculture, Bureau of Entomology. Loose-Leaf Manual of Insect Control.
Mayer, D. F., J. D. Lunden, and L. Rathbone. 1987. Evaluation of Insecticides for Thrips tabaci (Thysanoptera: Thripidae) and Effects of Thrips on Bulb Onions. J. Econ. Ent. 80(4): 930-932.
Saini, R. K., A. S. Dahiya and A. N. Verma. 1989. Field Evaluation of Some Insecticides Against Onion Thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae). Haryama Ag. Univ. J. Res. 19(4): 336-342.
Shelton, A. M. and R. C. North. 1987. Injury and Control of Onion Thrips (Thysanoptera: Thripidae) on Edible Podded Peas. J. Econ. Ent. 80(6): 1325-1350.
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Waterhouse, D. F. 1987. Thrips tabaci Lindeman, Thysanoptera: Thripidae, onion thrips. In Biological Control: Pacific Prospects -- Supplement 1. (Ed. D.F. Waterhouse and K.R. Norris). Inkata Press, Melbourne, Australia.
Zimmerman, E. C. 1948. Thrips (Thrips) tabaci Lindeman. pp. 422-425. In Insects of Hawaii. A Manual of the Insects of the Hawaiian Islands, including Enumeration of the Species and notes on the Origin, Distribution, Hosts, Parasites, etc. volume. 2: Apterygota to Thysanoptera. The University Press of Hawaii, Honolulu. 475 pages.