Characterization of queen-specific components of the fluid released by fighting honey bee queens

Swarming honey bee (<i>Apis mellifera</i> L.) colonies rear supernumerary young queens that compete for the limited resources (workers) necessary for founding a new colony. Young queens often fight to death. During fights, queens often release rectal fluid with a strong smell of grapes, after which they temporarily stop fighting. This potentially reduces the risk of deadly injury. The fluid and one of its components, <i>ortho</i>-aminoacetophenone, were previously found to have a pheromonal effect on workers. Recently, it has been suggested that the effects of this substance may be context- or concentration-specific. We performed semi-quantitative gas-chromatography mass spectrometry (GC/MS) analysis of the fluid (i) released by queens during their first fight, (ii) released during a subsequent fight, and (iii) obtained by dissecting the hindgut of queens and (iv) of workers. Following preliminary results by Page <i>et al.</i> (Experientia 44:270-271), we scored presence/absence of eight substances. Five substances (<i>ortho</i>-aminoacetophenone, decanoic acid, dodecanoic acid, octyl decanoate, and decyl decanoate) were characteristic of queens only. <i>ortho</i>-Aminoacetophenone was detected in all queens and in none of the workers, in agreement with previous findings that worker rectal contents do not have pheromonal effect. The fluid released by queens on their second fight also contained <i>ortho</i>-aminoacetophenone, but in smaller quantities. This study confirms the unique presence in queens of five compounds, demonstrates their rectal origin, and estimates the amount of <i>ortho</i>-aminoacetophenone released during fights, as required to design experiments addressing the function and adaptive significance of fluid release behaviour.