| Biology |
| 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. |
 |
| Distribution |
| 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. |
| Recognition |
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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online
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