Different functions of two alarm substances in the honeybee

In the honeybee, isopentyl acetate and 2-heptanone are described as alarm substances. We asked whether both substances have a similar role by testing the effect of their exposure on the appetitive proboscis extension reflex and on the aversive stinging reflex. In the appetitive context of sucrose stimulation no differences were found between isopentyl acetate and 2-heptanone. Small amounts of isopentyl acetate or 2-heptanone (3 microl of 1:9 dilution) yielded a response similar to that of a non-exposed control. Larger amounts of both substances (125 microl of 1:9 dilutions) as well as mixtures led to a decrease of responsiveness to sucrose. In the aversive context of electrical stimulation, significant differences between isopentyl acetate and 2-heptanone were found. Exposure to a small amount of isopentyl acetate (3 microl of 1:9 dilution) or to a large amount of 2-heptanone (125 microl of 1:9 dilution) led to an increase of responsiveness to the electric shock. Larger quantities of isopentyl acetate (125 microl of 1:9 dilution) decreased the responsiveness to the shock. 2-Heptanone never decreased the responsiveness to the shock. Our results indicate that isopentyl acetate and 2-heptanone have different functions even if both are capable of evoking deterrent responses in a defensive context.