No abstract

In the ambrosia beetle Trypodendron lineatum (Oliver) (Coleoptera: Scolytidae) a large number of olfactory receptor cells were identified keyed to the pheromone (+)-lineatin. No cell responding to pheromones adhering to other bark beetle genera was found. This indicates that T. lineatum do not benefit from recognizing other bark beetle species when colonizing a host. The results support previous field results that e-pinene and ethanol are signals of significance for T. lineatum. However, concerning c~-pinene it should not be excluded that an other component might instead be the key odour.Results obtained by the combined gas chromatographical (GC) separation with electrophysiological single cell recordings, suggested that host odour cells respond to one or a few compounds and that minor constituents are rather important. Selective responses of a few cells to non-liost volatiles further suggest that such signals may play a role as repellents or inhibitors when the beetles search for a host.

A field test with synthetic dimethyl trisulphide as attractant in flight traps was carried out in Finnmark, northern Norway, in July 1992 and. The reindeer oestrids Hypoderma (= Oedemagena) tarandi (L.) and Cephenemyia trompe (Modeer) (Diptera: Oestridae), previously shown to react positively to dimethyl trisulphide on the olfactory receptor level, were only caught in small numbers, with no significant differences between baited and unbaited traps. In both years, however, the baited traps caught significantly more individuals of Calliphoridae and Hydrotaea anxia (Zetterstedt) (Diptera: Muscidae) than unbaited control traps. In 1992, Protophormia terraenovae (Robineau-Desvoidy) (Diptera: Calliphoridae) and H. anxia were the predominant species (78.5% and 20.5%, respectively). In 1994, H. anxia was the most prevalent species (73.6%). Seven species of Calliphoridae were caught, with P. terraenovae, Calliphora vomitoria (L.), C. uralensis (Villeneuve) and C. loewi (Enderlain) as the most numerous ones. Dimethyl trisulphide is probably a decomposition product from bacterial activity and may be one of the major cues for calliphorid host finding. The significance of the reaction for oestrids on the receptor level, but evidently not on a behavioural level, remains unclear.

Short Communicationsimply that secondarily formed metabolites II and/or III might play a behavioral role as a part of a male pheromone in their courtship sequence, and also potentially function as an allomone against predators. Rigorous work will be needed to clarify the ecological significance of the phenylpropanoid -fruit fly association. Acknowledgment. We thank Dr H. Etoh of Meijo University for providing us with the synthetic sample of compound II and useful comments, and Mr A. Denis of Universiti Sains Malaysia for technical assistance. We are also grateful to Dr K. Matsushita and N. Fujii of JEOL. Co. Ltd., for the measurement of nuclear Overhauser effects using JNM GX-400 (400 MHz).Summary. Sticky traps containing (+)-lineatin, the pheromone of the ambrosia beetle, Trypodendron lineatum, attracted the predator Thanasimus formicarius to about the same extent as traps baited with ipslure, the pheromone blend used for mass-trapping Ips typographus. The results indicate that T. lineatum is an important prey for T. formicarius early in the season before the main prey becomes active. Addition of exo-brevicomin to ipslure and ethanol and/or c~-pinene to (+)-lineatin did not significantly influence the catches of the predator.

Olfactory receptor cells were studied electrophysiologically inIps typographus andDendroctonus micans. The investigation revealed cells which were keyed to pheromone compounds characteristic of the reciprocal genus. Thus, cells keyed toexo-brevicomin were found inI. typographus, whereas cells keyed to (+)-ipsdienol were present inD. micans. Laboratory behavioral tests indicated an attractive effect of the two compounds on beetles of the reciprocal genus. InI. typographus the effect ofexo-brevicomin predominantly concerned males and enhanced their response to the pheromone "ipslure." It is suggested thatexo-brevicomin serves as an interspecific attractant forI. typographus, which may be guided by pheromone compounds of the reciprocal genus in finding suitable breeding material. The function of (+)-ipsdienol inD. micans is more uncertain. It may be either a pheromone or an interspecific messenger.