Reception of bark beetle pheromone in the predaceous clerid beetle,Thanasimus formicarius (Coleoptera: Cleridae)

Summary

The antennal olfactory receptors of the predatory clerid beetle,Thanasimus formicarius (L.), are as sensitive as the receptors of its prey, the scolytid beetleIps typographus (L.), to ipsdienol, (S)-cis-verbenol and 2,3,2-methylbutenol, suggested components of the aggregation pheromone of this bark beetle.

The two species were stimulated under identical conditions and comparisons were made between electroantennogram (EAG) responses to synthetic pheromonal compounds of various species of bark beetles. At threshold concentrations for eliciting EAG responses,T. formicarius has almost equal sensitivity to most of the tested substances, whileI. typographus is more sensitive to ipsdienol and (S)-cis-verbenol, putative components of its conspecific aggregation pheromone used in long distance communication, than to its suggested antiaggregation pheromone, ipsenol (Fig. 6). In both species (S)-(+)-ipsdienol is the most effective of the tested compounds. The dose response curves of verbenol isomers reside close to the curve of (S)-(+)-ipsdienol in the clerid beetle, while in the bark beetle these isomers are much less effective than (S)-(+)-ipsdienol at high stimulus doses (Fig. 7).

Recordings from single olfactory cells ofsensilla basiconica inT. formicarius demonstrated an olfactory function of this sensillum type (Figs. 1, 3). The individual receptor cells had broad reaction spectra to the test substances; however, enantiomeric discrimination could be obtained through the response of these receptor cells (Fig. 4). The morphology and distribution of sensilla on the antenna ofT. formicarius were investigated by scanning electron microscopy (SEM).

It is suggested that the apparent strategy used byT. formicarius for finding its prey is to perceive various bark beetle and tree volatiles, then after determining the ‘quality’ of the perceived mixture of odours, to approach the emitter of a preferred mixture. The kairomonal response ofT. formicarius toI. typographus could be due to a mixture of (S)-(+)-ipsdienol, (S)-(−)-ipsenol and (S)-cis-verbenol.