Scirtothrips dorsalis, the chilli thripsThis is the more common international spelling of "chilli" outside of the United States. This spelling has been preserved in the common name for the insect by entomologists in the United States in deference to the body of literature already published for this species by international authors. or yellow tea thrips, is an extremely successful invasive species of pest-thripsMorse, JG; Hoddle, MS (2005). Invasion biology of thrips. Annual Review of Entomology 51: 67 – 89. which has expanded rapidly from Asia over the last twenty years, and is gradually achieving a global distribution. It has most recently been reported in St. Vincent (2004) Florida (2005), Texas (2006), and Puerto Rico (2007). It is a pest of economic significance with a broad host range, with prominent pest reports on crops including pepper, eggplant, mango, citrus, strawberry, grapes, cotton, tea, peanuts, blueberry, and roses. Chilli thrips appear to feed preferentially on new growth, and infested plants usually develop characteristic wrinkled leaves, with distinctive brown scarring along the veins of leaves, the buds of flowers, and the calyx of fruit. Feeding damage can reduce the sale value of crops produced, and in sufficient numbers, kill plants already aggravated by environmental stress. This thrips has also been implicated in the transmission of three tospoviruses, but there is some controversy over its efficiency as a vector.Whitfield AE, Ullman DE, German TL (2005). Tospovirus-thrips interactions. Annual Review of Phytopathology. 43: 459–89.
This thrips has a rapid life cycle, and can develop from egg to adult in slightly less than two weeks under optimal weather conditions.
Identification A tentative (but inconclusive) field identification can be made of this thrips by searching for the following traits under low power magnification: small size (under a millimeter in length), yellow coloration, dark antennae, and dark striping on the lower abdomen.Skarlinsky, T. 2004. Identification Aid for Scirtothrips dorsalis Hood, 1919, pp. 6. In USDA [ed.]. unpublished.Seal, D; Ciomperlik, MA (2004). Surveys of St. Lucia and St. Vincent for Scirtothrips dorsalis (Hood), Jan. 14-23, 2004. USDA APHIS PPQ, Technical Report. 19 pp.Seal, D; Ciomperlik, MA; Richards, ML; Klassen, W (2006). Distribution of Scirtothrips dorsalis (Thysanoptera: Thripidae) in pepper fields and on pepper plants in St. Vincent. Florida Entomologist 89: 311 – 320.
It can be specifically identified and confirmed through the presence of forked sense cones on antennal segments III and IV, antennomeres I-II are pale and III to IX are dark; there are three discal setae on the lateral margins of abdominal tergites, with pronotal posteromarginal seta II nearly one and a half times the length of I or III, a complete posteromarginal comb on tergite VII; and three ocellar setae with III between posterior ocelli.Mound, L. A., and J. M. Palmer. 1981. Identification, distribution and host-plants of the pest species of Scirtothrips (Thysanoptera: Thripidae). Bulletin of Entomological Research 71: 467–479.Hoddle, M. S., and L. A. Mound. 2003. The genus Scirtothips in Australia (Insecta, Thysanoptera, Thripidae). Zootaxa 268: 1 - 40.
Recent research concludes that S. dorsalis does represent a species complex of three or more disparate species who are morphologically similar but genetically distinct.Hoddle, M. S., J. M. Heraty, P. F. Rugman-Jones, L. A. Mound, and R. Stouthamer. 2008. Relationships Among Species of Scirtothrips (Thysanoptera: Thripidae, Thripinae) Using Molecular and Morphological Data. Annals of the Entomological Society of America 101: 491 – 500.Dickey AM, Kumar V, Hoddle MS, Funderburk JE, Morgan JK, Jara-Cavieres A. 2015. "The Scirtothrips dorsalis Species Complex: Endemism and Invasion in a Global Pest." PLoS ONE. 10(4): e0123747. doi:10.1371/journal.pone.0123747
Biology Like all thrips of suborder Terebrantia, S. dorsalis undergoes two nymphal stages followed by two "false" pupal stages,Dev, H. N. 1964. Preliminary studies on the biology of the Assam thrips, Scirtothrips dorsalis Hood, on tea. Indian Journal of Entomology 26: 184–194. and under optimal conditions, this thrips may reach adulthood in approximately two weeks. However, research has shown that the length of these life-history stages are flexible within a group depending on an individual's access to nutrientsMound, L. A. 2005. Thysanoptera: diversity and interactions. Annual Review of Entomology 50: 247–269. and temperature.Tatara, A. 1994. Effect of temperature and host plant on the development, fertility, and longevity of Scirtothrips dorsalis Hood (Thysanoptera: Thripidae). Applied Entomology and Zoology 29: 31 - 37. Nymphs entering the metamorphic process drop off of the plant during the first of two propual stages, and then complete their development in loose soil or leaf litter at the base of their host - but have been observed to pupate in any dark and humid crevice low on the plant, including bark and the folds of tightly packed lower leavesOkada, T., M. Otaishi, and T. Kaneko. 1981. Diurnal change in activity of adults of Scirtothrips dorsalis Hood. Japanese Journal of Applied Entomology and Zoology 48: 44 - 46. or flowers. The pupal process can range from two days to a full week. In temperate regions where the temperature falls below the critical lower threshold, non-diapausing adults are reported to overwinter in the soil or apical buds.Shibao, M., F. Tanaka, and F. Nakasuji. 1990. Seasonal changes and infestation sites of the chillie thrips, Scirtothrips dorsalis (Thysanoptera: Thripidae) on grapes. Japanese Journal of Applied Entomology and Zoology 34: 145–152.Okada, T., and I. Kudo. 1982. Overwintering sites and stages of Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) in Tea fields. Japanese Journal of Applied Entomology and Zoology 26: 177–182.Okada, T., and I. Kudo. 1982. Relative abundance and phenology of Thysanoptera in a Tea field. Japanese Journal of Applied Entomology and Zoology 26. Colder temperatures may even drive pupation, but this has not been experimentally confirmed.
Post-emergence, females have a pre-oviposition period of one to two days. Using their ovipositor, females lay single eggs within the plant tissue,Lewis, T. 1973. Thrips. Their biology, ecology and economic importance. Academic Press, London, GB. and may lay an average of forty eggs during their lifetime. Females of S. dorsalis prefer to lay their eggs inside of young leaves and buds at the apical meristem of plants, but as populations increase, will lay their eggs within the surface of mature leaves.Raizada, U. 1965. Life history of Scirtothrips dorsalis Hood with detailed external morphology of the immature stage. Bulletin of Entomology 6: 30 - 49. Depending on temperature, eggs may gestate for one to three weeks. After hatching, larvae will migrate from older leaves to the newer growth at terminals.Onkarappa, S., and B. Mallik. 1998. Distribution and management of Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) on rose, pp. 165–167. In P. P. Reddy, N. K. Kumar and A. Verghese [eds.], Advances in IPM for horticultural crops. Indian Institute of Horticultural Research, Bangalore, India. Like many thrips, S. dorsalis appears to prefer feeding on new growth and young plants, and is often found on the newer top leaves on smaller plants, although individual plant morphology and chemistry may result in some distributional differences.
Nymph populations will continue to increase so long as new shoots are allowed to grow,Shibao, M., F. Tanaka, K. Fujisaki, and F. Nakasuji. 1993. Effects of lateral shoot cutting on population density of the chillie Thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) on Grape. Applied Entomology and Zoology 28: 35 - 41. and adults are permitted to land.Shibao, M. 1996. Effects of a Vinyl Film Cover on the Population Density of the Chillie Thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), on Grape. Applied Entomology and Zoology 31: 174–177. Physically manipulating the host by removing preferred feeding sites has been shown to reduce thrips density on the plant, but also to increase the relative rate of between-plot dispersal.Shibao, M. 1997. Effects of Resource Availability on Population Density of the Chillie Thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), on Grape. Applied Entomology and Zoology 32: 413–415.
History of Expansion Molecular evidence currently suggests that the point of biogeographical origin for the thrips is in Southeast Asia or on the Indian subcontinent, but the original host remains unknown. Chili peppers did not arrive in India until the sixteenth and seventeenth centuries with Portuguese traders,Collingham, E. 2006. Curry: A Tale of Cooks and Conquerors. Oxford University Press. so the host upon which S. dorsalis was first described cannot be the point of origin. Given S. dorsalis’ broad polyphagy and long history of pestilent behavior, it has been speculated that a weed such as castor that was adopted for agriculture may have been one of several hosts of origin, and that the thrips adapted and began to exploit other hosts as they became available in the changing agricultural landscape.
It spread rapidly throughout the contiguous region of southeastern Asia fairly early, and there are many historical instances of these thrips attacking key crops on a regular basis. In India, it has been described as a pest of castor, pepper,Varadharajan, S., and R. Veeravel. 1995. Population dynamics of chilli thrips Scirtothrips dorsalis Hood in Annamalainagar. Indian Journal of Ecology 22: 27 - 30. cotton,Panickar, B. K., and J. R. Patel. 2001. Population dynamics of different species of thrips on chilli, cotton, and pigeonpea. Indian Journal of Entomology 63: 170–175. tea,Mukhopadhyay, A., S. Sannigrahi, and G. Biswas. 1997. Colonization and utilization of young tea plants by some insects and mites in Darjeeling foothills. Ecology and evolution of plant-feeding insects in natural and man-made environments.: 59 69. mango, and peanut.Wheatley, A. R. D., J. A. Wightman, J. H. Williams, and S. J. Wheatley. 1989. The influence of drought stress on the distribution of insect on four groundnut genotypes grown near Hyderabad, India. Bulletin of Entomological Research 79: 567–578. Outside of India, it has been reported as pest in China on tea and fruits like litchi,Li, J.-M., G.-W. Liu, and R.-B. Peng. 2004. Bionomics and control of the yellow tea thrips, Scirothrips dorsalis infesting litchi. Entomological Knowledge 41: 172–173. in Taiwan on citrus and vegetable,Chang, N. T. 1995. Major pest thrips in Taiwan, pp. 105–108. In B. L. Parker, M. Skinner and T. Lewis [eds.], Thrips Biology and Management. Plenum Press, New York. on citrus and tea in Japan,Tatara, A., and K. Furuhashi. 1992. Analytical Study on Damage to Satsuma Mandarin Fruit by Scirtothrips dorsalis Hood (Thysanoptera : Thripidae), with Particular Reference to Pest Density. Japanese Journal of Applied Entomology and Zoology 36: 217–223. many vegetable and fruit crops in Thailand,Bansiddhi, K., and S. Poonchaisri. 1995. Thrips of vegetables in Thailand, pp. 109–110. In B. L. Parker, M. Skinner and T. Lewis [eds.], Thrips Biology and Management. Plenum Press, New York. peppers and mango in Vietnam, and even seasonally on the Korean peninsula.Lee, G.-S., J.-H. Lee, S.-H. Kang, and K.-S. Woo. 2001. Thrips species (Thysanoptera: Thripidae) in winter season and their vernal activities on Jeju Island, Korea. . Journal of Asia-Pacific Entomology 4: 115–122.