Frankliniella occidentalis (Pergande, 1895)

This species breeds on a wide range of plants, in flowers and on leaves, and causes serious crop losses both through feeding damage and as an important vector of tospoviruses. However, it can also be a useful predator of spider mites on some crops such as cotton.
Originally from the South Western States of the USA, the western flower thrips is now widespread around the world. It has become established in areas with a Mediterranean climate, but in colder areas it is found in greenhouses. It is not a pest in the lowlands of the wet tropics, although it is sometimes abundant at high elevations in such countries, including Kenya and Malaya.
Female macropterous; body colour variable from yellow to brown in SW of USA, but widespread pest strain usually mainly dark yellow with brown areas medially on each tergite; antennal segments II & VI-VIII brown, III – V yellow with apices variably brown; legs mainly yellow washed with brown; forewing pale with dark setae. Antennae 8-segmented, III & IV with forked sense cone, VIII longer than VII. Head wider than long; 3 pairs of ocellar setae present, pair III longer than distance between external margins of hind ocelli, arising on anterior margins of ocellar triangle; postocular setae pair I present, pair IV longer than distance between hind ocelli. Pronotum with 5 pairs of major setae; anteromarginal setae slightly shorter than anteroangulars, one pair of minor setae present medially between posteromarginal submedian setae. Metanotum with 2 pairs of setae at anterior margin, campaniform sensilla present. Forewing with 2 complete rows of veinal setae. Tergites V-VIII with pair of lateral ctenidia, ctenidia sometimes weakly developed on IV, on VIII anterolateral of spiracle; posteromarginal comb on VIII complete, with short slender microtrichia arising from triangular bases. Sternites III-VII without discal setae.
Male similar to female but smaller and paler; tergite VIII without marginal comb; IX with median pair of dorsal setae shorter than lateral pair, posterolateral setae stout in larger males; sternites III-VII with transverse glandular area.
Second instar larva white, antennae weakly shaded, tergite IX not with shaded transverse band extending just anterior to major setae; tergites with transverse rows of small, weakly developed, linear plaques, dorsal setae all blunt; tergite IX campaniform sensilla wide apart, almost anterior to setae B2, posterior margin with complete row of well-developed teeth.
Related species
In its natural environment, F. occidentalis is remarkably variable in size and colour, as well as in structural details. The dark brown form has been found commonly in the Californian mountains in Spring, but is replaced in Summer by the pale yellow form. The widespread pest strain is more constant in size and colour, but dark forms are sometimes found in areas with low temperatures such as in winter insouthern Queensland, Australia. From most members of the genus, F. occidentalis can be recognised by the pale forewings, long postocular setae, presence of metanotal campaniform sensilla, and the rather irregular comb on tergite VIII.

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