Thysanoptera Californica

Endemic thrips of California

Little is known of the biology of most of the thrips species that are considered native to California, despite the efforts of Dudley Moulton and Stanley Bailey, two eminent specialists who were long-term residents of this State. Not only is there a lack of knowledge of the biology of the recorded species, but recent collecting has suggested that more species live in this area than are currently known. There is great opportunity for interesting discoveries on this fauna, as indicated by a series of publications on the arid fauna by Wiesenborn since 2000 (see ThripsWiki, 2019).

The thrips fauna of California includes some remarkable elements. Two of the smallest Thysanoptera families worldwide, the Stenurothripidae (=Adiheterothripidae) and the Fauriellidae, are both represented in California. The first of these derives its name from fossils in Cretaceous Amber from about 100 million years ago, although only three genera of living species are included in the family. Two of these three genera are known only from California, whilst the third genus, Holarthrothrips, comprises four species found in the flowers of Phoenix (date palm) trees between the Mediterranean and India. The second small family, the Fauriellidae, comprises five species arranged in four genera, one from California, one from the Mediterranean area, and two from southeast Africa. Similar discontinuous distributions occur in the genus Orothrips (Aeolothripidae) with one species in the Mediterranean area and two in California. Currently there is no biogeographic explanation for these discontinuous distributions between western North America and the European Mediterranean.

In addition to these unusual elements, the Californian thrips fauna seems curiously asymmetric. The genus Dactuliothrips (Aeolothripidae) comprises nine species in the western parts of the Americas, with five species in California but the others in South America. Similarly, Ankothrips (Melanthripidae) comprises 13 species, of which seven are from Western USA and four from Europe. Members of these two genera are large and spectacular, but there are few observations on their behavior and biology, and no ecological explanation for their diversity in California. More problematic is the presence in California of over 20 species of the genus Aeolothrips (Aeolothripidae). Members of this genus are commonly regarded as facultative predators, and thus might be expected to exhibit limited host specificity. Judging from the available descriptions, particularly of males, the diversity of Aeolothrips species in California constitutes a remarkable radiation and an interesting biological phenomenon. In the family Phlaeothripidae, nine species of Leptothrips are listed from California, and 12 species of Liothrips, and the seven described species of Bagnalliella are all from the Western arid zone in association with Yucca species. However, species recognition in these three genera remains unsatisfactory, particularly because of the lack of reliable observations on their host-associations. The genus Thrips (Thripidae) includes at least 25 species in California, and at least 16 species of Frankliniella are listed from this State (Hoddle et al., 2004), but again, little is known of their biology other than the pest species.

The Californian thrips fauna is noticeably different from, and less diverse than, the thrips fauna of eastern USA. In particular, the large suite of leaf-litter species related to the genus Eurythrips that is so abundant in the eastern States (Mound, 1976, 1977) is not known to be represented in California. Moreover, in Florida (Diffie et al., 2008), possibly as a result of the more humid climate, the thrips fauna includes a much larger proportion of Neotropical species that are presumably windborne northwards from the Caribbean. Of particular interest in Western USA is the sharp faunal discontinuity in the region of the Mexican border. Only a single species of the very large and worldwide genus Thrips is considered to be native to the area south of this border, and the number of large fungus-feeding thrips species increases rapidly southwards through Mexico into Central America.