Reevaluation of the chemical secretion of the sternal glands of Polistes social wasps (Hymenoptera Vespidae)

In a previous paper we reported the presence of long chain fatty acids (lauric, myristic, palmitoleic, palmitic, linoleic, oleic, stearic) in the sternal glands of social wasps of the genus Polistes. These glands had been reported by several authors to be the source of ant repellents that these wasps apply on their nests. Among the identified acids, we found that the unsaturated ones had an ant repellent effect.. More recently, sampling (through SPME) from the bristly area corresponding to the sternal glands (van der Vecht organ) of live R dominulus revealed that this contains the same hydrocarbons as the cuticle and only minor quantities of fatty acids. This is in contrast to the amount of fatty acids we previously found in excised glands sampled either directly by headspace SPME or by solid sampling following derivatisation with diazomethane. By repeating the analysis on the sternal glands and on some tissues with no glandular function, we found that the same fatty acids were ubiquitously present. Furthermore, new bioassays have shown that long chain methyl esters, alkanes and alkenes have a similar repellent effect to fatty acids on the ant Monomorium pharaonis, provided they are liquid at room temperature. These results questioned our previous report that fatty acids are characteristic components of sternal gland secretion and suggest that other long chain compounds may also play a significant role in the defence of the nest.