Basswood Thrips: Appearance, Territory, Damage, and Life Cycle

Latin Name: Thrips calcaratus Uzel (Thysanoptera: Thripidae)

Appearance: T. calcaratus biology is poorly understood. This species has not been investigated beyond the taxonomic level since it is not a pest in its native European habitat.

Hosts Plants: This species feeds on American basswood in North America (T. americana).

Territory: The species ranges from New England and Quebec to Ontario, Pennsylvania, New York, and the Great Lake States.

Damage Insect Cause: Thrips calcaratus Uzel is a European species that has become invasive in eastern North America. Basswood thrips have rasping/sucking mouthparts and feed on buds, particularly those of American basswood, in early spring (Tilia americana L.). Defoliation can occur as a result of bud-feeding because mature leaves become distorted or torn. Defoliation of American basswood on a regular basis lowers tree development and increases the rate of dieback from other reasons. The species is important in northern Wisconsin, where damaging epidemics occur.

Life History and Habits: As an adult, T. calcaratus spends the winter under the earth. Emergence occurs in southern Wisconsin during the first week of May, and in northern counties approximately a week later. The emergence is very synchronized, with the south nearing completion by the end of the second week of May and the north nearing completion by late May.

The appearance of adults corresponds with the swelling of basswood buds. They feed on the opening buds, just as the leaves begin to grow. If the leaves get chlorotic, they will ultimately fall off. Oviposition appears to occur in the bottom leaf surface’s major veins. Larvae arrive in early June, by which time there are very few adults left.

Larvae mature in June, fall to the ground, and burrow into the earth. Soil populations outnumber litter populations by a wide margin. The majority of T. calcaratus reach adulthood by mid-July, with some immatures remaining until September. Each year, one generation is born.