The introduced basswood thrips is of European origin. Because it has not caused damage in its native European range, its basic biology, host range and life history are not well known.
Preliminary research suggests that egg production and thrips development are optimal at cooler temperatures. Adult females emerge from overwintering sites in the soil as basswood buds break in early spring. Adults feed on the newly opened leaves, rupturing individual plant cells. Oviposition (egg laying) occurs within the lower leaf veins of expanding leaves. Reproduction is parthenogenetic (females do not mate). No males have been recorded in North America.
Larvae appear in mid- to late May, and feed on leaf tissue throughout their development. At least two larval instars are recognized. Fully developed larvae drop from the foliage, move into the litter and soil, and pupate. Adults emerge from pupae later in the summer, move into the soil, and diapause until the following spring.
In addition to the introduced basswood thrips, the pear thrips, Taeniothrips inconsequens, may potentially defoliate deciduous forests of the Lake States. Other thrips that may be present on basswood include the native basswood thrips, Neahydatothrips tiliae, which is not known to cause damage, and the beneficial predatory thrips, Haplothnps mali.
Introduced basswood thrips adults have 7-segmented antennae and a pre-apical fore tarsal claw. Larvae have 17 to 18 projections on the posterior abdominal comb In contrast, adult pear thrips have 8-segmented antennae and an apical fore tarsal claw. Larval pear thrips have only 7 to 8 projections on the posterior abdominal comb. Both the native basswood thrips, which is white with red ocelli, and the predatory thrips, which is large and black, are easily distinguished from the basswood thrips.
Knowledge of the basic biology of the introduced basswood thrips, as well as its host range and impact of repeated defoliation, will be required in order to make sound resource management decisions.
Raffa, K. F. and D. J. Hall. 1989. Thrips calcaratus Uzel (Thysanoptera: Thripidae), a new pest of basswood trees in the Great Lakes region. Can. J. For. Res. 19:1662-1663.
Raffa, K. F. 1991. Biology and impact of Thrips calcaratus Uzel in the Great Lakes region. Pages 317-324, in B. L. Parker, M. Skinner and T. Lewis (eds.). Towards Understanding Thysanoptera. USDA For. Serv. Gen. Tech. Rep. NE-147.
Lynne K. Rieske
Steven A. Katovich
Kenneth F. Raffa