Distribution of bark insects in ?island? plantations of spruce (Picea abies (L.) Karst.) in subarctic Norway

Abstract

Eleven isolated plantations of Norway spruce Picea abies (L.) Karst, in Troms county, northern Norway, were examined for bark insects in summers 1990 and 1991. Field-infested bolts from controlled fellings were reared in laboratory to complement field-investigations. Results are compared to records made from the same plantations 1974–78. Eight scolytid species, two curculionids and two cerambycids were found inhabiting spruce in 1990–91. Dryocoetes autographus was found in ten, and Tetropium castaneum in 9 plantations. Hylastes cunicularius has apparently expanded its distribution since 1978. One plantation had no bark insects confined to spruce, except old galleries of Pityogenes chalcographus. No new immigrants to the region were found, but one curculionid species may have become extinct. Reproduction of Dryocoetes autographus and Tetropium castaneum was studied in the laboratory. D. autographus bred consecutive generations from the same bolt, whereas T. castaneum displayed varying generation time, partly within the same bolt. This enhances their viability in plantations where felling activity is low. Several scolytid species widely distributed elsewhere in naturally spruce-forested areas in Scandinavia north of the Arctic circle are still absent in Troms, including all the smallest species. It is suggested that the success of colonizers in unpredictable climates depends on both dispersal capabilities (larger species have a higher dispersal power than the smallest species), life cycle flexibility and versatility in habitat requirements. It is concluded that only species with certain properties have established in the plantations, i.e. the immigration and colonization is not stochastic.