Western flower thrips

The western flower thrips is an invasive pest insect in agriculture. This species of thrips is native to the Southwestern United States but has spread to other continents, including Europe, Australia (where it was identified in May 1993), and South America via transport of infested plant material. It has been documented to feed on over 500 different species of host plants, including a large number of fruit, vegetable, and ornamental crops. The adult male is about 1 mm long; the female is slightly larger, about 1.4 mm in length. Most western flower thrips are female and reproduce by arrhenotokous parthenogenesis; i.e. females can produce males from unfertilized eggs, but females arise only from fertilized eggs. Males are rare, and are always pale yellow, while females vary in color, often by season, from red to yellow to dark brown. Each adult is elongated and thin, with two pairs of long wings. The eggs are oval or kidney-shaped, white, and about 0.2 mm long. The nymph is yellowish in color with red eyes. The lifecycle of the western flower thrips varies in length due to temperature, with the adult living from two to five or more weeks, and the nymph stage lasting from five to 20 days. Each female may lay 40 to over 100 eggs in the tissues of the plant, often in the flower, but also in the fruit or foliage. The newly hatched nymph feeds on the plant for two of its instars, then falls off the plant to complete its other two instar stages. The insect damages the plant in several ways. The major damage is caused by the adult ovipositing in the plant tissue. The plant is also injured by feeding, which leaves holes and areas of silvery discoloration when the plant reacts to the insect's saliva. Nymphs feed heavily on new fruit just beginning to develop from the flower. The western flower thrips is also the major vector of tomato spotted wilt virus, a serious plant disease. Western flower thrips are a year-round pest, but are less destructive during wet weather. Damage can be reduced by growing barriers of nonhost plants around crops and by eliminating reservoir plants, plants to which the thrips are especially attracted, such as jimson weed. The thrips' natural enemies include pirate bugs of genus Orius. Other agents show promise as biological pest control, including the fungus Metarhizium anisopliae, and the mirid Dicyphus hesperus. Flower-feeding thrips are routinely attracted to bright floral colors, especially white, blue, and yellow, and will land and attempt to feed. Some flower thrips will 'bite' humans wearing clothing with such bright colors, though no species feed on blood; such biting does not result in any known disease transmission, but skin irritations are known to occur.