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.), str essed by the aback on resinous trees produce large amounts of l-5-(1-h ydroxy-1-methylethyl)-cyclohexa-1,3-diene. The compound appears to be derived from Delta(3)-carene and acts as a repellent. Males of Ips typ ographus (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 de scribed. The occurrence of (+)-grandisol and other compounds related t o weevil pheromones points to a close relation between Scolytidae and Curculionidae. Females of Dendroctonus simplex (Le Conte) use (-)-fron talin as the main pheromone. 6-Methyl-6-hepten-2-one, a minor componen t among the volatile compounds released by the females, is regarded as a possible precursor of frontalin. Similarly, (1-hydroxy-1-methylethy l)-5-methyltetrahydrofuran, pityol, a pheromone of Pityophthorus spp., is regarded to at least share a common biogenetic precursor with 6-me thyl-5-hepten-2-ol, sulcatol. A new bicylic acetal, -ethyl-1,5-dimethy l-6,8-dioxabicyclo[3.2.1]octane, is described as an aggregation pherom one of the beech bark beetle, Taphrorychus bicolor (Herbst). Structura l relationships between bark beetle pheromones and plant volatiles are discussed.