Male labial gland secretions as species recognition signals in species of Bombus

Abstract

Abstract Spring queens of Bombus cryptarum from Europe, Bombus burjaeticus from the Russian Transbaikal region and Bombus moderatus from North America were collected at different localities to grow artificial colonies and obtain fresh males. Furthermore, males of Bombus florilegus , B. moderatus , Bombus magnus and Bombus occidentalis were collected in the field. Cephalic labial gland secretions of 29 specimens from these different taxa were analysed by gas chromatography/mass spectrometry (GC/MS). About 50 compounds were identified, including a mixture of straight-chain fatty acid derivatives (alkenoles, acids, acetates and esters), and the usual pattern of saturated and unsaturated hydrocarbons C 21 –C 29 . The secretions of all specimens investigated were very similar: ethyl dodecanoate was identified as the main component (90–97% peak area). Since the sum of percentage peak areas for the hydrocarbons amounted up to 3–6%, most of the remaining compounds (8 alkenoles, 6 acids, 6 acetates and 20 esters) could only be detected at very low levels ( B. florilegus , each taxon had a sympatric bumblebee taxon that also used ethyl dodecanoate as the main component: B. magnus , sympatric with B. cryptarum in Europe, Bombus patagiatus , sympatric with B. burjaeticus in the Russian Transbaikal and B. occidentalis , sympatric with B. moderatus in North America. Male cephalic labial gland secretions of 20 specimens from these sympatric taxa were also investigated to see how far their pattern of compounds differed from that of the cryptarum complex taxa ( cryptarum – burjaeticus – florilegus – moderatus ). Besides some quantitative differences in ethyl dodecanoate and ethyl octadec-9-enoate, the occurrence of octadeca-9,12-dien-1-ol, octadeca-9,12,15-trien-1-ol and octadec-11-en-1-ol was an essential qualitative difference that separated the labial gland secretions of B. magnus , B. patagiatus and B. occidentalis from those of their sympatric counterparts. A principal component analysis confirmed this separation. Due to their low variability and differences in pattern of compounds compared to those of closely related sympatric bumblebees, the labial gland secretions of B. cryptarum , B. burjaeticus, B. florilegus and B. moderatus distributed across Europe, the Russian Far East and North America are very well suited to function as ‘species recognition signal’. The taxonomic consequences for the cryptarum complex taxa and their relationship to Bombus albocinctus from the Russian Far East are discussed in context of recent genetic investigations.