SEMIOCHEMICALS FROM BARK BEETLES - NEW RESULTS, REMARKS, AND REFLECTIONS

A brief survey is given about recent results in the identification of semiochemicals in bark beetles: Males of lps sexdentatus (Boern.), stressed by the aback on resinous trees produce large amounts of (3S)-1-methyl-5-(1-hydroxy-1-methylethyl)-cyclohexa-1,3-diene. The compound appears to be derived from Delta(3)-carene and acts as a repellent. Males of Ips typographus (L.), stressed through the attack on unsuitable host material release 3-methyl-7-methylene-1,3(E), 8-nonatriene, which seems to act as a repellent. The odor bouquet of three species of Pityogenes is described. The occurrence of (+)-grandisol and other compounds related to weevil pheromones points to a close relation between Scolytidae and Curculionidae. Females of Dendroctonus simplex (Le Conte) use (-)-frontalin as the main pheromone. 6-Methyl-6-hepten-2-one, a minor component among the volatile compounds released by the females, is regarded as a possible precursor of frontalin. Similarly, (2R,5S)-2(1-hydroxy-1-methylethyl)-5-methyltetrahydrofuran, pityol, a pheromone of Pityophthorus spp., is regarded to at least share a common biogenetic precursor with 6-methyl-5-hepten-2-ol, sulcatol. A new bicylic acetal, 2-ethyl-1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane, is described as an aggregation pheromone of the beech bark beetle, Taphrorychus bicolor (Herbst). Structural relationships between bark beetle pheromones and plant volatiles are discussed.