Gladiolus thrips (Thrips simplex)
Pest description and damage Adult thrips emerge milky-white but soon turn brown and begin feeding. The female is approximately 0.06 inch (1.65 mm) long and slightly larger than the male. The egg is about 0.0125 inch (0.3 mm) long, opaque white, smooth, and bean-shaped. Eggs are deposited in the leaf tissue and corms. Thrips feed by rasping the surface of the leaves or corms, which causes plant juices to flow. The affected leaf surfaces turn a whitish-gray and eventually dry out and turn brown. Infested flowers are discolored and spotted and entire spikes may fail to bloom. Affected corms are discolored and deformed, and are prone to decay. Plants do not develop normally from such corms.
Biology and life history These thrips are native to Africa and cannot overwinter outdoors where temperatures consistently drop below 50°F. The thrips are brought into previously uninfested gardens or greenhouses on infested corms. These thrips can overwinter at any stage on stored corms or on plants growing in greenhouses. The life cycle consists of six stages: the egg, two larval instars, two pupal instars and the adult stage. Females deposit 100 to 200 eggs. During the warm growing season, the development of the gladiolus thrips can occur in about 2 weeks. With such rapid development, the thrips can have nine or more generations outside during the growing season. The eggs are deposited in the leaves of gladioli or in the corms in storage. Larvae and pupae can be found in the buds or leaf sheaths, although the larvae often drop to the ground to transform into the quiescent pupae. Adult gladiolus thrips live 35 to 40 days.
Pest monitoring Observe growth for spotting or bleaching of foliage, or for plants that fail to grow vigorously. Bloom stalks may shrivel as though dry.
Some control of thrips by predatory mites is possible. Hypoaspis miles and Amblyseiulus cucumeris are both considered to be effective predators of mites and possibly thrips.
Storing corms at cool temperatures will eliminate all life stages of the thrips from the corms. After being kept in cold storage for a minimum period of 6 weeks at 35.6°F or 8 weeks at 41°F, larvae, pupae, and adult specimens died and eggs were no longer viable. Hence, the corms were damaged no further. Storage of corms at these low temperatures, provided they were well dried, proved not to be harmful to emergence and growth. Prompt removal of infested plants and corms once symptoms are noted helps arrest spread within a planting to uninfested plants.
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For more information
Antonelli, A.L. 2003. Thrips. WSU Puyallup REC. PLS-36 (http://www.puyallup.wsu.edu/plantclinic/resources/pdf/pls36thrips.pdf)