The number of thrips species, listed in the "Table of introduced and potential invaders", that have been inadvertently introduced to California, presumably through human activities, is now over 60. Some of these will have been introduced many years ago, such as the greenhouse thrips, Heliothrips haemorrhoidalis, and the fern thrips Leucothrips nigripennis, both of which presumably came from Southern Brazil (Mound, 1999; Nakahara et al., 2015). One Oriental species, Liothrips floridensis on Cinnamomum camphora leaves, has been known in Florida for many years, but was recognised in California only in 2011. In contrast, Scirtothrips perseae and Neohydatothrips burungae have both been found in California only in recent years, both of them in association with the avocado orchards (Hoddle, 2002). Similarly, the Oriental gall-invading species, Androthrips ramachandrai, has been recorded from California only very recently, together with Gynaikothrips uzeli, the leaf-rolling thrips on Ficus benjiamina (Boyd & Held, 2006). Another recent introduction is Klambothrips myopori from southeastern Australia (Cameron & Mound, 2014), a black thrips that induces severe damage to the shrub Myoporum laetum that is so widely grown along roadsides in California. Moreover, a healthy population of Dendrothrips howei, another Australian species, was discovered at a Los Angeles plant nursery in 2010.
Such invasions are continuing, largely as a result of the international horticultural trade transporting large numbers of plants by air. During the peak marketing seasons in North America, up to 35 flights have been reported to leave Colombia daily, fully laden with plants and flowers for Miami and Los Angeles. Because of this massive trade in horticultural produce, the identification and information system presented here includes 40 species that are currently not established in California, but that are considered potential immigrants, particularly from Hawaii. For example, the citrus pest, Pezothrips kellyanus, and a Pacific flower thrips, Thrips maculicollis, have both been intercepted many times at Sacramento in floral leis arriving from Hawaii.
There is limited biological or geographical pattern concerning the origin of the immigrant species. Early European settlement involving sailing ships presumably introduced many thrips, such as grass-living species associated with hay (Limothrips cerealium) or within grass seeds (Chirothrips manicatus), and several fungus-feeding species arrived presumably on dead wood (Mound, 1983). One species, Cartomothrips browni, has been widely distributed around the world from Australia in the seed capsules of various Eucalyptus species. Another, Amynothrips andersoni, has been introduced to California deliberately, as a biological control agent against a weedy plant. However, most of the introduced species are phytophages that have presumably been transported accidentally on live plants.
The species listed below as potentially invasive include a range of widespread pests in warmer parts of the world, such as the red-banded cocoa thrips, Selenothrips rubrocinctus, and the melon thrips, Thrips palmi, as well as the Southeast Asian species, Thrips parvispinus, that is now a pest in Hawaii. Also included are species from the Caribbean area, Frankliniella bispinosa, F. cephalica, F invasor and F. parvula. The horticultural trade in Ficus species has introduced the Oriental species Anascirtothrips arorai into Florida, and several other species that are common in the Caribbean must be considered potential immigrants to California, including Haplothrips gowdeyi, Anaphothrips sudanensis and the crop virus vector species Frankliniella schultzei. Again, there is little pattern to the species selected for this list except that all of them have been found in association with crops in other parts of the world. Two further potential immigrants are the rice thrips, Stenchaetothrips biformis, and some of the thrips associated with sugar cane such as Podothrips lucasseni.
Boyd DW & Held DW (2006) Androthrips ramachandrai (Thysanoptera: Phlaeothripidae): an introduced thrips in the United States. Florida Entomologist 89: 455–458.
Cameron SL & Mound LA (2014) Trans-Bass Strait speciation and trans-Pacific dispersal in the Myoporum thrips (Thysanoptera, Phlaeothripinae). Austral Entomology 53: 36–41.
Hoddle MS (2002) Developmental and reproductive biology of Scirtothrips perseae (Thysanoptera: Thripidae): a new avocado pest in California. Bulletin of Entomological Research 92: 279–285.
Mound LA (1983) Natural and disrupted patterns of geographical distribution in Thysanoptera (Insecta). Journal of Biogeography 10: 119–133.
Mound LA (1999) Saltatorial leaf–feeding Thysanoptera (Thripidae, Dendrothripinae) in Australia and New Caledonia, with newly recorded pests of ferns, figs and mulberries. Australian Journal of Entomology 38: 257–273.
Nakahara S, O’Donnell CA & Mound LA (2015) Heliothrips haemorrhoidalis and its relatives, with one new species and one new genus (Thysanoptera). Zootaxa 4021 (4): 578–584.