Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 115

240

Thrips tabaci Lindeman ( 240-241 )
syn. Thrips debilis Bagnell
Onion thrips
An often common pest of cultivated plants, including
ornamentals such as Asparagus plumosus, Begonia ,
carnation ( Dianthus caryophyllus ), Chrysanthemum,
Cineraria, Cyclamen, Dahlia, Gerbera and orchids.
Most damaging in greenhouses; also a virus vector.
Cosmopolitan. Widely distributed in Europe.

DESCRIPTION
Adult female: 1.0-1.3 mm long; greyish yellow to
brown; antennae 7-segmented and yellowish brown;
fore wings pale brownish yellow; comb of setae on hind
margin of eighth abdominal tergite complete. Nymph:
whitish to pale yellowish-orange.

240 Onion thrips ( Thrips tabaci ) damage to leaf of Dianthus .

241

LIFE HISTORY
Under favourable conditions this entirely
parthenogenetic species breeds continuously. Eggs are
laid in plant tissue and hatch within 1-2 weeks. Two
nymphal stages then occur on host plants, fully fed
nymphs dropping to the ground about a week later. They
then enter the soil, where the transformation to the adult
stage takes place, again in about a week. Considerable
populations may develop on greenhouse-grown plants;
greenhouses are also subject to frequent invasion by
outdoor populations. In unprotected situations, several
broods occur from May through to winter, and adult
females usually overwinter in the soil. 241 Onion thrips ( Thrips tabaci ) damage to flower of

Cyclamen .

DAMAGE
Affected leaves become flecked extensively with silver,
damage typically being associated with black grains of
frass; flower petals may also become discoloured and
distorted. Attacks are most severe in hot, dry conditions.

Thrips nigropilosis Uzel
Chrysanthemum thrips
Generally common and sometimes troublesome on
greenhouse-grown Chrysanthemum , producing
characteristic brownish-red marks at the base of leaf
stalks and brownish warts on the foliage. Adults occur
throughout the year, with several broods of nymphs
developing from May to November. The adults are
1.2 mm long, and mainly yellow with brownish
markings, pale yellow fore wings and 7-segmented
antennae; some adults may have reduced wings. The
main outdoor hosts are plantains, especially ribwort
plantain ( Plantago lanceolata ).

Thrips atratus Haliday
Carnation thrips
This generally abundant species occurs throughout the
year, breeding on various outdoor plants from May
onwards. Adults (1.3-1.8 mm long) are mainly dark
brown, with 8-segmented antennae and narrow, brown
(basally paler) fore wings. They commonly enter
greenhouses from June to September, and may then
cause damage to flowers of carnation ( Dianthus
caryophyllus ) and pink ( D. plumarius ).