Western flower thrips

The western flower thrips (Frankliniella occidentalis) is one of the most dangerous pests of vegetable, ornamental and flower plants in greenhouses. It is an object of quarantine in many countries. The pest is a wide polyphage. It has a high adaptive ability. Its high degree of resistance to synthetic pesticides is inherent for European population. Frankliniella occidentalis is an agent of plant virus diseases.

Biology. Life cycle

The color of a body varies from dark-brown to light-yellow. There are spots in form of two grey-brown strips on the last segments. The length of a male body is to 0.9 mm. The female is 1.2 mm in length. The head is transversal. Its length without a mouth conus is 1.3–1.5 times as less than the width above eyes. The antennae are 8-segmented, the first segments are a little lighter than others. The pre-thorax is transversal with folds on hind corners. There are chaetae (bristles) on the tops of them. The wings are transparent, light-yellow, without spots and strips. They are narrow and have a curved frontal edge. The length of wings is 0.6 of body length. There are legs of run type. The light individuals have the yellow color of legs. The dark individuals have brown legs with yellow tarsi (paws). The egg is bean-shaped with a size of 0.2 mm. It is light after laying and it becomes dark later. The larva is light-yellow. In dependence on age its size is 0.5–1.2 mm.

Mode of life

The morphological and the biological characteristics of this pest are similar to the characteristics of distinct-stage insects (complete metamorphosis). The 1st age larva begins to feed in 2–3 hours after emergence from the egg. The molt of this larva stage occurs in 3–4 days. The larvae of the 2nd age differ from the larvae of the 1st age by larger size and some changes of body coloration. Besides, the head of the 2nd larva stage is bigger, and a body covering is thin and transparent. In 3–4 days the larva reaches the size of an adult individual. Then it ceases feeding and goes in the ground in a depth of 5–6 cm where molting occurs. There the larva is transformed into the motionless stage of a pronymph and a nymph. The pronymph and the nymph don't feed. In molting periods some limited peculiar motions are inherent to them. The formation of an adult insect occurs in this stage of development. The life span of females is a few more than the life span of males and amounts to 27–45 days. The fertility of Frankliniella occidentalis is 200–250 eggs.

The optimal temperature for species development is 15–30°C. The minimal temperature is 9.5°C. The duration of development from an egg to an adult at a temperature of 26–29°C is 10 days. In greenhouses the species is able to reproduce 7–12 generations. The adult insects fly quite well.

Symptoms of injures

The larvae and the adult individuals suck out cell sap from plant tissues. Initially this process causes the emergence of yellow necrotic spots and streak disease. Gradually these spots and streaks join. Injured plant tissue dies off. As a result of it holes are formed, leaves wither and fall. Under the intensive development of pest population the deformation and the twisting of shoots can be observed. The injuring of flower buds causes flower deformations. The specific sign of cucumber affection by pest is the curl of flowers and the crumple of fruit ovaries. When the pest colonizes rose flower buds it can cause their deformation and withering. The pest is able to transfer the viruses of plant diseases.