|Scientific Name||Frankliniella occidentalis (Pergande)|
|Common Names||English: Western Flower Thrips; German: Kalifornischer Blütenthrips; French: Thrips de Californie; Spanish: Trips de California, Trips occidental de flores; Italian: Nuovo fitomizo delle serre|
|Description||The adult has a slender, flattened body, about 1 mm (male) (0.039 inch) and 1.5 mm (female) (0.06 inch) in length. There are three color forms, pale yellow, intermediate and dark brown. The four wings, in rest folded lengthwise, consist for the most part of fringes. At their feet the insects have bladderlike adhesive organs which allow them to walk on extremely smooth surfaces.|
With their mouth parts, thrips puncture individual plant cells, mostly in the epidermis, and suck up their sap. The empty, air-filled tissue causes the plant surface to get a characteristic silvery appearance. Heavier infestations will lead to browning and wilting of leaf tips, in extreme cases to shoot distortions and dropping of leaves. When fruits or vegetables are attacked, scarring can occur. Distinctive black spots of frass are left at the feeding sites. Egg-laying causes unsightly suberised marks due to the plant's reaction. F. occidentalis is strongly attracted to brightly colored flowers, which will consequently show discolored spots and become deformed; buds may fail to open. Ornamentals will thus be gravely blemished and rendered unmarketable.
In other crops, even more important than the direct damage as described is that by transmitted diseases. F. occidentalis is an important vector of Tospoviruses, namely of Tomato spotted wilt virus, which can cause severe reduction in quality and yield of many crops. In persons repeatedly exposed to great numbers of the insects skin and respiratory irritations have occasionally been observed.
Thrips have an unusual form of incomplete metamorphosis. There are four nymphal instars. They are all mobile, but only the first two, actually called larvae, are able to ingest food. The third and fourth are called prepupa and pupa, respectively.
Development is largely dependent on temperature. Hatching occurs about 3-4 days after the egg has been laid, the nymphal stage can last from 5 to 20 days. Adults are mature about 3 days after emerging, they can live up to 30 days. F. occidentalis is facultatively parthenogenetic.
In warm regions or in greenhouses, where continuous breeding is possible, it can have up to 12-15 generations per year. Otherwise, adults and pupae will overwinter in sheltered places like under lumps of soil, tree bark, in grass and weeds etc., and only one or two generations may be completed. In spring, the adults migrate to flowering plants and start with oviposition. The female lays about 40-50 eggs, 1-2 per day. Each is inserted singly into the plant tissue in a way that part of it remains protruding.
All thrips are poor fliers, but easily transported passively by the wind. The origin of F. occidentalis is in North America. In the 1980s it was by chance introduced to Europe. Meanwhile, it has been spread with international trade throughout subtropical and temperate regions of the world. In colder climates it is frequently a serious pest in greenhouses.
Additional Crop Information
F. occidentalis is a polyphagous species. Causes damage on more than fifty genera and about 200 species of crops, including fruit trees, vegetables and ornamentals.
Due to its wide host range and its importance as a vector F. occidentalis is considered one of the world's major pests.
Integrated Crop Management
Meticulous examination of aquired plant material is important in greenhouses to prevent introduction. Special gauze netting can in many cases be used to keep thrips out.
Generally, early detection of an infestation is essential for successful control. F. occidentalis is difficult to find because of its behavior trait always to hide deep between leaves or petals.
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