Population levels and flight phenology of bark beetle predators in stands with and without previous infestations of the bark beetle Tomicus piniperda

Relative population levels and flight periods of Tomicus piniperda (L.) (Co l.:Scolytidae) and two of its main predators, Thanasimus formicarius (L.) ( Col.: Cleridae) and Rhizophagus depressus (F.) (Col.: Monotomidae) were mon itored in 1995 in eight Scots pine stands in central Sweden using flight ba rrier traps (five per stand) baited with alpha-pinene and ethanol. In four of the stands (A-stands) T. piniperda and associated species had reproduced the previous year in stumps and slash remaining after thinnings conducted in the winter of 1993/1994. In the remaining four stands (B-stands) no bark beetle breeding material had been available during the five preceding year s. In addition, the flight periods of the species were monitored in one sta nd in 1996. In 1995 the catches of T. piniperda and R. depressus were four to five times higher in the A-stands than in the B-stands, whereas there wa s no difference in the catch of T. formicarius between the two kinds of sta nds. The T. formicarius/T. piniperda ratio was ca. 50 times higher in the B -stands compared with the A-stands during the period of clerid predation on colonising bark beetle adults and six times higher during the period of cl erid oviposition. The R. depressus/T. piniperda ratio was only slightly hig her in the A-strands than in the B-stands as a result of the spatial distri bution of T. piniperda. Three additional species of bark beetle predators w ere caught: Glischrochilus quadripunctatus (L.), Pityophagus ferrugineus (F .) (Col.: Nitidulidae) and Rhizophagus ferrugineus (Payk.) (Col.: Monotomid ae). Based on their seasonal abundance the bark beetle predators can be div ided into three temporal groups: the first species to occur in the spring i s G. quadripuctatus, the second group consists of R. depressus and T. formi carius, and the last species to initiate flight are R. ferrugineus and P. f errugineus. (C) 1999 Elsevier Science B.V. All rights reserved.