Both sexes fully winged. Body brown, tarsi yellowish, also apex of mid and hind tibiae; major setae brown; antennae brown, segment III paler; fore wings brown, base pale. Head wider than long; two pairs of ocellar setae; pair III arising on anterior margins of ocellar triangle; postocular setae pair I almost as long as ocellar setae III. Antennae 7-segmented; segments III–IV with short forked sensorium. Pronotum with many distinct transverse lines; 2 pairs of long posteroangular setae; posterior margin with 3 pairs of setae. Metanotum with irregularly elongate reticulation, transverse at anterior; median setae arising behind anterior margin; campaniform sensilla present. Fore wing first vein with 3 (or 2) setae on distal half; second vein with row of about 14 setae. Abdominal tergite II with 3 lateral marginal setae; sculpture on median tergites not extending to median pair of tergal setae; V–VIII with paired ctenidia laterally, on VIII posteromesad to spiracles; tergite VIII posteromarginal comb absent medially, with irregular slender microtrichia laterally; pleurotergites without discal setae, sculpture lines bearing dentate microtrichia. Sternite II with 2 pairs of marginal setae, III–VII with 3 pairs; sternites without discal setae.
Male smaller than female; tergite VIII comb absent; sternites III–VI with transversely oval pore plate.
The genus Thrips is the second largest genus in the Thysanoptera, and currently includes, worldwide, about 285 species. T. madronii appears to be a particularly common flower thrips in California. It has been compared by Nakahara (1994) both to a species found in the eastern States, T. varipes Hood, and to the widespread European T. major Uzel, but it differs from both of these in having dentate, not ciliate, microtrichia on the pleurotergites. It can also be confused with T. magnus, but that has the pronotum with weaker sculpture, and the males have pore plates on sternites III–VII. All members of genus Thrips lack ocellar setae I on the head, and they all have ctenidia on tergite VIII posteromesad to the spiracles. Other characters, such as number of antennal segments, number of setae on the fore wing veins, and number of discal setae on the sternites are variable between species (Palmer, 1992; Nakahara, 1994; Mound & Masumoto, 2005).
Thrips madronii Moulton
Presumably breeding in flowers.
Adults have been taken from plants in a range of families with no recognized specificity.
California, Oregon, Washington, British Columbia, Mexico.