Methanol, acetaldehyde, and ethanol have been identified in extracts of attractive wood and bark. The attractancy induced by anaerobic treatment in both sapwood and phloem of conifers and broadleaf trees was characterized by ethanol as the most concentrated component. In laboratory bioassays, ethanol was attractive at low concentration to both sexes of Trypodendron lineatum (Olivier). Methanol and acetaldehyde, at the concentrations found, apparently play no role in attraction. Monoterpenes had a repellent effect on T. lineatum.

Detection of weakened hosts from a distance by bark beetles through olfaction was investigated in field experiments. No significant numbers of Scolytidae were attracted to anaerobically treated pine bolts, stem disks, or sugar and ponderosa pine bark including phloem. Treatment of living trees with cacodylic acid induced attacks byDendroctonus brevicomis, D. ponderosae, Ips latidens, Gnathotrichus retusus, andPityophthorus scalptor, beginning two weeks after treatment. There was no significant difference between landing rates ofD. brevicomis andD. ponderosae on screened treated trees and screened controls. There was a significant increase in landing rates ofG. retusus andI. latidens, because both species had penetrated the screen and produced pheromones. Tree frilling alone did not increase the landing rate of bark beetles. Freezing of the lower trunk with dry ice did not increase significantly the landing rate ofD. brevicomis, D. ponderosae, G. retusus, orI. latidens on screened trees, whereas unscreened frozen trees were attacked by all four species. There was no significantly higher landing rate byD. brevicomis, D. ponderosae, I. paraconfusus, I. latidens, G. retusus, orHylurgops subcostulatus on screened trees evidencing symptoms of severe infection by the root pathogenVerticicladiella wagenerii, than on symptornless trees. These experiments show thatD. brevicomis, D. ponderosae, I. paraconfusus, I. latidens, andG. retusus land, apparently indiscriminately, on healthy and stressed hosts. Thus, in these species host discrimination must occur after landing and prior to sustained feeding.

No abstract

The antennae of the ambrosia beetle Trypodendron lineaturn (Olivier) were examined with the light and electron microscopes to determine the types, distribution, and structure of sense organs found thereon. Six main types of sense organs are present, with an additional seventh cuticular structure, the hypodermal gland pore, which is thought to be non-sensory.Sensilla chaetica possess one bipolar neuron terminating in a scolopale at the base of the thick-walled articulated hair.Type I sensilla trichodea are short articulated hairs of unknown fine structure and innervation. Type 11 sensilla trichodca are sharp-pointed hairs of intermediate length, with thin, perforated hair walls, and two neurons with slightly branched dendrites in the hair lumen. Type I11 sensil la trichodea are blunt-tipped, reversely curved hairs possessing a double lumen and four to scven bipolar neurons. the unbranched dendrites of which extend to the hair tip.Sensilla basiconica are short t hin-walled perforated hairs or pegs. possessing two neurons each, with many-branched dendrites. The relationship of dendrite branches to hair perforations is not clear.Sensilla campaniformia consist of a subsurface dome in the center of which lies the nerve ending of one neuron similar to that of the sensilla chaetica.Evidence is presented, indicating the probable absence of sensory axon fusion in the antennae.

Can. Ent. 123: 295-298 (1991)