Olfactory recognition of host-tree susceptibility by pine shoot beetles

Abstract

Storm-fallen Scots pines with broken roots and trees with severed tops exude wound oleoresin. These trees are susceptible to bark beetles due to an injured vascular system that can not provide adequate oleoresin in order to resist new attacks by beetles [I]. Once a tree is attacked, most bark beetles use pheromone attractants to locate mates and often to overcome tree resistance through a mass attack [I, 21. It would be clearly advantageous for bark beetles to have evolved sensory systems for efficiently locating their host and in recognizing whether a particular host was less resistant than most healthy trees. However, little is known of how bark beetles select their host from among other plant and tree species [I], or what may attract the first individuals to a susceptible host. We have investigated the semiochemical basis of the mass aggregation of pine shoot beetles, Tomicus piniperda, on storm-injured Scots pine. We found that the beetle can recognize while still in flight a host tree and whether it is susceptible by means of olfaction of three plant monoterpenes evaporating from wound oleoresin. Scots pine logs infested with males and females of T. piniperda were tested in the forest of southern Sweden (Table 1, 1982) to determine their attractiveness to naturally swarming populations in the spring. The resulting catches of beetles indicate that there was a strong attraction to volatiles released from logs