Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Host trees and emergence of Megastigmus specularis Walley (Hym., Torymidae).

Abstract

Cones were collected in 1968 from 13 species of Abies (fir) in Finland and kept under observation for the emergence of Megastigmus, larvae of which had been found in samples of seeds collected during earlier studies on the cones. The only species reared was M. specularis Walley [cf. RAE/A 46, p. 267], which was known to be abundant in seeds of A. sibirica in Finland. A table is given showing ten other species of Abies from the cones of which the Torymid was reared and the extent of the infestation. The most most heavily infested were A. lasiocarpa, A. sachalinensis and A. sibirica. Adults emerged between mid-June and early July from seeds kept in rearing boxes and from fallen seeds. Males emerged slightly earlier than females; oviposition in the seeds began as soon as the females emerged. The larvae overwinter in the seeds, under the snow cover on the ground, and some remain in diapause until after the second or even the third winter. Studies in which infested seeds were removed to 25 deg C after chilling showed that a period of 180 days at 0 deg C sufficed for the termination of diapause in the males, but that four months of 5 deg C or three months at 10 deg C were necessary before diapause was terminated in both sexes.