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

Abstract

Relative population levels and flight periods of Tomicus piniperda (L.) (Col.: Scolytidae) and two of its main predators, Thanasimus formicarius (L.) (Col.: Cleridae) and Rhizophagus depressus (F.) (Col.: Monotomidae) were monitored in 1995 in eight Scots pine stands in central Sweden using flight barrier traps (five per stand) baited with α-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 years. In addition, the flight periods of the species were monitored in one stand 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 was no difference in the catch of T. formicarius between the two kinds of stands. 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 clerid oviposition. The R. depressus/ T. piniperda ratio was only slightly higher in the A-strands than in the B-stands as a result of the spatial distribution of T. piniperda. Three additional species of bark beetle predators were caught: Glischrochilus quadripunctatus (L.), Pityophagus ferrugineus (F.) (Col.: Nitidulidae) and Rhizophagus ferrugineus (Payk.) (Col.: Monotomidae). Based on their seasonal abundance the bark beetle predators can be divided into three temporal groups: the first species to occur in the spring is G. quadripunctatus, the second group consists of R. depressus and T. formicarius, and the last species to initiate flight are R. ferrugineus and P. ferrugineus.