Description: There are more than 6,000 thrips species known in the world. A common pest found in greenhouses, and ornamental and vegetable gardens, they damage plants by sucking their juices, and scraping at fruits, flowers and leaves. Leaves may turn pale, splotchy and silvery, then die. Injured plants are twisted, discolored and scarred. Extremely active, thrips feed in large groups and leap or fly away when disturbed. Host plants include onions, beans, carrots, squash and many other garden vegetables and many flowers, especially gladioli and roses.
Adults are very small (less than 1/25 inch) straw-colored or black slender insects with two pairs of feathery wings. Without the use of a hand lens, they resemble tiny dark threads. Both adults and the wingless larvae are attracted to white, yellow and other light colored blossoms and are responsible for spreading tomato spotted wilt virus and impatiens necrotic spot virus.
Life Cycle: Adults and pupae overwinter in garden soil. In spring, newly emerged females insert eggs into the tissues of flowers, leaves or stems. (They do not need to mate for reproduction.) Each female can produce up to 80 eggs, which hatch within days in warm weather, or weeks to months in colder weather. They become wingless larvae (nymphs), which feed on plant sap. After two or more nymphal stages, many thrips drop to the soil to pupate. Emerging adults fly to the plant and repeat the cycle. There may be 12-15 generations per year with the entire cycle from egg to adult requiring less than 16 days in warm weather.
Thrips Control: Remove weeds and grass from around garden areas to eliminate alternate hosts. Blue sticky traps are helpful for monitoring adult populations. If found, use the Bug Blaster or hose off plants with a strong stream of water to reduce pest numbers. Release commercially available beneficial insects, such as minute pirate bugs, thrips predators, ladybugs and lacewing, to attack and destroy all stages of thrips. For best results, make releases when pest levels are low to medium. If populations are high, use a least-toxic, short-lived natural insecticide to establish control, then release predatory insects to maintain control. Insecticidal soap, spinosad, neem oil and botanical insecticides can be used to spot treat heavily infested areas. Clean up crop debris, especially onion leaves after harvest.
Tip: When using contact insecticides it is necessary to provide thorough coverage, especially inside the plant base of the leaves where the majority of pests are located.
Photo Credit: College of Tropical Agriculture and Human Resources, University of Hawaii