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Thrips taxa introduced to California

The number of thrips species that have been inadvertently introduced to California, presumably through human activities, is now 56. 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 & Monteiro, 1997; Mound, 1999). In contrast, Scirtothrips perseae and Neohydatothrips burungae have both been found in California only in the past 10 years, both of them in association with the avocado orchards (Hoddle, 2002). Moreover, the Oriental gall-invading species, Androthrips ramachandrai, has been recorded from California only very recently (Boyd & Held, 2006). Such invasions are continuing, largely as a result of the expanding international horticultural trade involving air, rather than sea, transport. For example, during the peak marketing seasons in North America, up to 35 flights leave Colombia each day fully laden with flowers mainly for Miami but with increasing numbers for Los Angeles. Because of this massive trade in horticultural produce, the identification and information system presented here includes a further 14 species that are considered to be potential immigrants.

There is little biological or geographical pattern to the immigrant species. Early European settlement involving sailing ships presumably introduced many species, such as grass-living thrips associated with hay (Limothrips) or within grass seeds (Chirothrips), and three fungus-feeding species were probably introduced on dead wood (Mound, 1983). At least one species has been introduced deliberately (Amynothrips), as a biological control agent against a weedy plant, but most species are phytophagous and have presumably been transported on live plants.

The species listed 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 two species from the Caribbean area, Frankliniella bispinosa and F. cephalica. 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. One exception is the inclusion of Oxythrips divisus; the reason for this is that there is an old and unsubstantiated record of a European species of this genus from California, so that some member of Oxythrips will presumably be found living in California.