Volatile chemicals of the ants Myrmica rubra L. and M. scabrinodis nyl.

Abstract

The most volatile constituents of the sting apparatus of the ants Myrmica rubra L. and M. scabrlnodis Nyl. have been examined by reaction gas chromatography and found to contain nanogramme quantities of simple alcohols, aldehydes and ketones.
A technique has been developed to permit the extraction of glandular liquid directly from the component glands of the sting apparatus. Essentially, for this technique, the appropriate gland was dissected from the ant, pierced with a fine glass tube and its contents withdrawn by capillary action. The filled portion of capillary was then sealed into a small glass ampoule and introduced into the gas chromatograph using an existing solid sampling technique. The technique was also used to calculate the volume and water content of the glandular liquid.
In both species, Dufour's gland contains between 100 ng and 150 ng of oxygenated volatiles dissolved in anhydrous hydrocarbons. The principal components are ethanal, propanone, methylpropanal, butenone and butanone with smaller quantities of methanol, ethanol, butanol and propanal.
The poison vesicle of both species also contains methanol, ethanal, ethanol, propanal, propanone, methylpropanal and butanone, together with 2- or 3-methylbutanal (probably the latter), butane, traces of methane, ethane and propane and three unidentified components. No butenone or butanol is present in this gland.
The concentration of the volatiles in the poison vesicle, where they are in aqueous solution, is some five times less than in Dufour's gland, but is still about twenty times greater than in the haemolymph.
It is suggested that these oxygenated compounds are deposited by older workers on their foraging area and are used as a recruitment pheromone to a freshly laid trail in the case of the poison vesicle secretion. In the Dufour's gland secretion the same compounds are volatilised relatively slowly from their hydrocarbon solution: they attract other workers and induce them to move in a rapid, sinuous and exploratory manner, thus serving as a recruitment and foraging pheromone for new territories.
Ethological tests performed in another laboratory on M. rubra have shown that three effects recognised earlier for the Dufour's gland can be attributed to four of its components. Ethanal synergised by ethanol produces an attractive effect on foraging workers. Propanone induces an increased linear speed, and changes in sinuousity of movement are induced by ethanol synergised by butanone. Ethanol, butanone or mixtures of all four compounds induce the deposition of Dufour's gland secretion on the foraging area.
The electrophysiological response of ants to these four compounds was assessed by recording their electroantennogram.
The poison vesicle contents of each species will induce trail following in either species, but none of the volatiles which have been tested was found to elicit trail following behaviour.