|
|
Close Help | ||||||||||||||
|
Introduction Bombus lucorum (L.) is a widely distributed bumblebee species, occurring through whole Palaearctic region. It is one of the most common species of bumblebees in Central and Northern Europe. Males are patrolling during their premating behaviour. They establish flight paths with scent marks on prominent objects and fly along these routes awaiting the appearance of females, attracted by a pheromone. The marking pheromone is produced in the cephalic part of their labial gland. The species of bumblebees (Bombus Latreille, 1802) belonging to the subgenus Bombus s.str. are often difficult to determine. Colour is variable in a relatively wide range and other morphological differences are often very fine and indistinct. Though, especially the representatives of "lucorum species group" are morphologically hardly recognisable. This group is formed in West and Central Europe by Bombus (s.str.) lucorum (Linnaeus, 1761) and two other closely related species - B. (s.str.) magnus Vogt, 1911 and B. (s.str.) cryptarum (Fabricius, 1775).
The great morphological similarity caused that both B. cryptarum and B. magnus have either been regarded as distinct species or have been synonymised with B. lucorum, sometimes even with B. terrestris. This fact led several authors to use other characteristics than morphological and morphometrical ones for the separation of these taxa. Enzyme electrophoresis (Scholl et al. 1983) or chemical composition of the marking pheromone of bumblebee males (Pamilo et al. 1997; Bertsch 1997) were studied with the aim to find a good tool for distinguishing individual species. Especially the second characteristics mentioned is known to be species-specific.
First analysis of the chemical composition of the labial gland secretion of B. lucorum males was reported by Calam (1969). He identified ethyl 9-tetradecenoate as the main component along with several minor components of the secretion. B. lucorum occurring in Sweden was studied extensively by Kullenberg et al. (1970) and Bergstr�m et al. (1973). In two localities on the island �land, individuals with wide variety of colours from light yellow to brown were found and their labial gland secretion was analysed. Based on the chemical composition of the secretion, Kullenberg et al. (1970) distinguished between the "blonde" form and the "dark" form. While the blonde form contained ethyl (Z)-9-tetradecenoate (1) as the main component, the dark form produced mainly ethyl dodecanoate (2). Loken (1973) refers the "dark" form to B. magnus, later Rasmont et al. (1986) indicated that the "dark" form can be interpreted as the male of B. cryptarum. This opinion was recently confirmed by Bertsch (1997), who gave a detailed chemical analysis of the male labial gland secretion of B. cryptarum.
All collected males belonged to the medium-blonde form according to Bergstr�m
et al. (1973). Labial glands of 26 B. lucorum males, collected in 7 localities
(Fig. 1) in the Czech Republic (1994-1999, both in Bohemia and Moravia), were extracted
in hexane and extracts were analysed by means of GC-MS.
Double bond positions were determined from mass spectra of the dimethyl disuphide adducts, the E/Z configurations from co-chromatography with standards on a DB-1 column. The labial gland secretion consisted of 60 compounds with ethyl (Z)-9-tetradecenoate being the main component in all analysed samples (Fig. 2). Statistically evaluated analytical data (Principle Component Analysis; PCA; Fig. 3) did not show significantly different groups of individuals.
Although the males collected in the Czech territory showed a variability in colours to certain extent, all individuals belonged to one "chemical" form. The qualitative and quantitative composition of the labial gland secretions were much more similar to the Scandinavian blonde form than to the dark form (Bergstr�m et al. 1973). Considering the latest literature on "lucorum species group", the Czech individuals studied were undoubtedly B. (s.str.) lucorum and none of them belonged to B. cryptarum or B. magnus (Bertsch 1997). Small differences between individuals observed were most probably due to the different age or physiological condition of collected males rather than due to different localities of their occurrence.
B. lucorum is the most common species from the "lucorum species group" in
the Czech Republic which is in agreement with the literature data for central Europe.
B. cryptarum and B. magnus must be rare in our territory nowadays as we
have not found any individuals that would belong to these species. It can be seen from
our results and from the latest literature that the composition of the labial gland
secretion is a reliable tool for determination of species in cases where morphological
traits fail or are difficult to use.
References
Bergstr�m, G., Kullenberg, B., St�llberg-Stenhagen, S.,:
Bertsch, A.:
Calam, D. H.:
Kullenberg, B., Bergstr�m, G., St�llberg-Stenhagen, S.:
Loken, A:
Pamilo, P., Teng�, J., Rasmont, P., Pirhonen, K., Pekkarinen, A., Kaarnama, E.:
Rasmont, P., Scholl, A., de Jonghe, R., Obrecht, E., Adamski, A.:
Scholl, A., Obrecht, E.:
Urbanov� K., Valterov� I., Hovorka O. Kindl J.:
Research team
Acknowledgement
Related themes on our web pages
Michal Hoskovec © 8.II.2006
|
