Onion thrips
The onion thrips (Thrips tabaci) is a wide spread pest injuring about 500 species of various plants. In the conditions of glass-covered ground it causes considerable harm to vegetable and flower-ornamental crops. In outdoor planting the pest often feeds on cucumbers, tomatoes, eggplants, melon crops, cabbage, salad, legume and various medicinal grasses. It is an agent of virus diseases.
Biology. Life cicle.
The female is light-yellow, sometimes dark, 0.8–0.9 mm in length. The head is transversal, chaetae (hairs) on the head are short. The antennae are grey, the 3rd segment is yellowish often darkened on a top. The femurs and the tibiae (shanks) are grayish. The fore wings are yellowish, sometimes grey-yellow. The chaetae on a body are dark-brown or blackish, sometimes light.
Life mode
Adult insects overwinter in the upper layer of ground in a depth of 5–7 cm or in plant remains. In the first part of April they begin to feed then can move to plants in greenhouses or to field crops. The female lays about 100 eggs on leaf tissue during 20–25 days. The larva hatches from an egg in 3–5 days. It feeds on leaves and in 8–10 days moves into the ground (to 15 cm in depth), where the larva is transformed into an imago in 4–5 days. The winged thrips emerges on the soil surface through cracks in the ground and colonize plants. The complete development of the thrips from egg laying to the emergence of the adult insect takes 15–20 days. Under outdoor planting in the South of Ukraine the onion thrips reproduces 3–5 generations, in the greenhouses it does 6–8 generations in a year.
Symptoms of injuries
The thrips and its larvae suck out sap from leaves, petals, stamens and ovaries. First it is formed an ajour net on the injured leaves, then yellowing appears and tissue dies off. It is possible to find slightly darkened or transparent spots on flowers — the places of insect punctures. The active development of the pest causes the premature falling of pedicles and immature fruits. Some flowers form underdeveloped ovaries producing small berries. The pest is an agent of plant virus diseases.
