Western Flower ThripsFrankliniella occidentalis

Frankliniella occidentalis, the western flower thrips, is a key pest of glasshouses, greenhouses and polytunnels.

Thrips can be difficult for growers to detect due to their small size and tendency for hiding within the concealed parts of the plant. Symptoms of plant damage by thrips include: bud deformation, shape distortion of fruits or vegetables during growth and a range of leaf spots and scars from thrips feeding. The larvae feed throughout the plant and leave the crop susceptible to secondary fungal and bacterial infection resulting in moulding and wilting.

Despite the small size of thrips at ~1mm in length the repercussions of Thrips infestations can be huge.

Western Flower Thrips
Biology

Thrips have six main life stages which includes the egg, two larval, prepupal, pupal and adult stages. Eggs are laid on the underside of leaves, flower structures or fruit. In some cases this can result in wart-like growths but in others it is undetectable.

Larvae mature through two instars in concealed and well-protected plant parts such as within flower petals or under the calyx of fruits. In heavy infestations the larval will become mobile as they attempt to nourish upon all parts of the plant that are above ground. Most thrips, including western flower thrips, fall to the ground in order to pupate.

Finally, the adult thrips will emerge with slender and fringed wings in order to take flight and seek a partner for reproduction.

Nature of Damage

Western flower thrips feeding often results in severly damaged crops. Growers may notice visible signs of damage such as bud and fruit deformities and a blackening of the skin. Female Thrips lay their eggs on crops and fruits, resulting in small discolorations surrounded by white rings. Thrip feeding will also affect the appearance of flowers.

The action of feeding enables entry of bacteria and fungi resulting in thrips being responsible for the spread of a number of plant diseases,  including the tomato spotted wilt virus and the necrotic spot virus.

Monitoring

Installation of blue sticky traps such as Optiroll sticky roller traps and Impact Blue boards from Russell IPM can provide a simple and effective monitoring system for the western flower thrips.

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