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Western Flower Thrip


Western Flower Thrip

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Caused By:-     The Thrip Frankliniella occidentalis


The Western Flower Thrips (WFT), Frankliniella occidentalis can be a serious insect pest on over 500 different species of plants.
They are native to North America, but as they can hide in plant materials they have now spread worldwide.
They are difficult to spot as they are very small with the adult male being only 1 mm long and the female is 1.4 mm in length.
The eggs are oval or kidney-shaped, white, and about 0.2 millimeters long and the nymphs are yellowish in colour with red eyes.
Their life cycle from eggs to adult takes around 14 days in a warm greenhouse.
In Greenhouses it can be active all year round and can lay over 200 eggs during their lifetime, but outside it is only active in the summer and is less destructive during wet weather.
WFT females give birth to large numbers of young and with their short reproductive cycles they increase their population faster than their predators, therefore early detection and control is essential in combatting this pest.
The newly hatched nymph feeds on the plant for a while, then falls off the plant to complete its development in the soil. This means that control measures must also include the soil sterilisation.
WFT damage plants in many ways, by the adult laying eggs in the plant tissue, by the nymphs feeding and injecting saliva into the plant tissue, which often transmit viruses into the plant. The feeding process causes leaf distortion, scars, holes and areas of silvery discolouration when the plant reacts to the insect's saliva. There may also be black feces present. Nymphs also feed on new fruit just beginning to develop from the flower and flowers may streaks and be discoloured.
As WFT is also the major carrier of many viruses this must also be considered in any eradication measures.
Picture by P.M.J. Ramakers, Applied Plant Research ,


The thrips' natural enemies include insects of genus Orius and Neoseilus, nematodes such as Thripinema nicklewoodii and fungi such as Beauveria bassiana and Metarhizium anisopliae.
They can be controlled by a combination of screening entrances to the greenhouses with fine mesh, cultural controls such as host weed control, soil sterilisation, environmental conditions, chemical controls, biological control and using indicator plants such as petunias to test for thrips.
As the eggs are laid inside the plant tissues they are well protected and because they often feed on flowers, where systemic insecticides often do not reach, few pesticide sprays are effective over a long periods as their short life cycle enables resistance to be developed very quickly.
There are many chemicals available, but improper use has led to many cases of pesticide resistance, therefore it is advisable to rotate the use of different chemicals.
Wherever WFT is detected there should also be a check for virus transmission.

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