Behavioural and electrophysiological responses of the bark beetle, Ips typographus, to potential pheromone components

Abstract

ABSTRACT. Field tests showed (S)‐(‐)‐cis‐verbenol and (R)‐(+)‐trans‐verbenol in combination with a second pheromonal component, 2‐methyl‐3‐buten‐2‐ol, more attractive than the combination with their optical antipodes. Inhibition of response to the attractant component, (S)‐(‐)‐cis‐verbenol, by high concentrations of its optical antipode did not occur. No significant differences were noted for response to the attractant, (S)‐(‐)‐cis‐verbenol and 2‐methyl‐3‐buten‐2‐ol, with the addition of either ipsdienol enantiomer or a racemic mixture of ipsdienol enantiomers. Electroantennogram (EAG) studies correlated well with the behavioural studies. EAGs recorded from male and female beetles revealed both sexes to have a lower threshold for the pheromone, (S)‐(‐)‐cis‐verbenol, than its host terpene precursor, (‐)‐alpha‐pinene. EAGs showed a greater number of acceptors for (‐)‐alpha‐pinene in males than in females. EAGs at acceptor saturation to the enantiomers of alpha‐pinene and the verbenol isomers showed males more responsive to (‐)‐alpha‐pinene, (±)‐cis‐verbenol, and (R)‐(+)‐trans‐verbenol. Significantly greater EAGs were elicited in females than in males to (‐)‐alpha‐pinene, and (±)‐ and (S)‐(‐)‐cis‐verbenol. No significant differences in EAGs of females to the enantiomers of trans‐verbenol were noted. EAGs showed similar thresholds in males and females to the pheromone component, 2‐methyl‐3‐buten‐2‐ol; however, female response at threshold was significantly greater than male response. The results are discussed with regard to olfactory acceptor evolution.