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Thrips (Thysanoptera)
There are two different sub-groups of Myriapoda, i.e. millipedes (Diplopoda) and centipedes (Symphyla).
Thrips are small, only 1-2 mm long slim insects with two pairs of fimbriated wings. The respective species are determined by the shape of the body and the bristles. At the end of their legs there are tarsal segments with small claws and adhesive bulbs. These insects have stinging and sucking mouthparts, they pierce into the cells and remove their contents. The cells fill with air and look silvery and shiny. Thrips are usually plant suckers, but there are also some predatory species.
The plant damaging thrips lay their eggs on leaves and other plant parts with the help of a ovipositor. Development stages are two wingless larvae stadiums and then two to three nymph stadiums with the nymphs having so-called stumpy wings. The first larvae stadium and the adults are very mobile whereas the nymphs have phases of immobility. The development depends mainly on temperature and light. In constantly favourable greenhouse conditions there will be about 10-12 generations per year, depending on the respective species.

Different varieties of orchids can be affected.

Western Flower Thrips (Frankliniella occidentalis Pergande): most frequent species in greenhouses, very polyphagous. The adults are about 2 mm long, light yellow to brown-yellow, the larvae are usually golden-yellow. The development cycles includes two larvae and two nymph stadiums and takes about 2-3 weeks in temperatures between 20°C and 30°C. This species usually lives in blossoms, but can also multiply rapidly on leaves and then severely damage all plant parts above the ground. This thrips species is a carrier of the tomato spotted wilt virus which occasionally infests Phalaenopsis plants. Thrips become resistant to insecticides relatively quick.

Tobacco Thrips (Thrips tabaci Lind.): very polyphagous, frequently found species, greenhouses are often infested by animals coming from outside. The adults are 1-1.3 mm long, grey-yellow to brown, sometimes nearly black, the larvae are white to yellow.
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