The onion thrips, Thrips tabaci Lindeman, is a worldwide
pest of vegetable crops. It ranges from tropical and subtropical
areas into the temperate regions.
The female onion thrips is about 1.0 mm long. The basic color
is yellowish-gray to dark-gray. Dark blotches may occur on the
thorax and abdomen.
The head has postocular setae
of about the same length as the interocellar
setae. The basal segments of the usually seven-segmented antennae
are light brown, while the distal segments are dark brown.
The prothorax has only two pairs
of well developed setae on the posterior margin. This characteristic
separates Thrips spp. from Frankliniella spp., which
have well developed setae along the anterior margin as well. The
second thoracic segment has convergent
striations on the top surface, and lacks campaniform sensillae.
The abdomen bears a well developed comb on segment VIII.
The onion thrips attack a wide range of crops and weeds, and is
well known for the damage it causes to onion, although other crops,
such as peas and cabbage also suffer damage (Hoy & Kretchman
1991, Shelton & North 1987, North & Shelton 1986).
The onion thrips is a well-known pest of onions. Damage consists
of feeding scars on the leaves. As the thrips congregate in the
tight sheath area, some damage may occur prior to detection. Where
feeding scars occur, foliar diseases, such as gray neck rot caused
by Botrytis allii Munn, may be more severe than
in an insect-free crop (Mayer et al. 1987).
The onion thrips is a vector of
tomato spotted wilt virus (Sakimura
1940, 1963). An awareness of prevalence of this disease in weeds
and other crops in a growing area is important. Early detection
of potential vectors is imperative if disease management is to
be effective. This is especially true in sensitive crops, such
as tomato, pepper, and lettuce.
In onion growing areas, where TSWV occurs, care should be taken
to avoid flushing large numbers of onion thrips out of onion fields
into adjacent crops, where they may acquire the virus. Weed management
in and around vegetable fields may also be critical in managing
this disease and its vector (Doederlein & Sites 1993, Edelson
et al. 1986).