|
Introduction Premating behaviour of bumblebee males consists of two parts: patrolling and scent-marking. The scent (marking pheromone) attracts conspecific females for mating. Marking pheromone is produced by the cephalic part of the male's labial gland. The gland secretions are species-specific and contain mostly two types of compounds. First are straight chain saturated and unsaturated hydrocarbons, alcohols, aldehydes, and esters. The second class is represented by terpenoids. In this study, we have focused on two bumblebee species - Bombus lucorum and Bombus lapidarius. Both species produce predominantly long-chain aliphatic compounds in the males' labial gland secretions. So far, there is no direct evidence how these compounds are biosynthesised in the labial gland, if common lipids found in the body are used as a pool material, or the components are biosynthesised de novo from acetate units.
Results After applications of deuterium labelled palmitic acid ([D31]-hexadecanoic acid) into either the head capsules or abdomens the corresponding deuterium labelled pheromone components were detected in the labial gland (LG) extracts of males of both species. In Bombus lucorum, ethyl [D29]-hexadec-9-enoate and ethyl [D31]-hexadecanoate were identified. No deuterium-labelled ethyl tetradecenoate, which would correspond to shortening of the carbon chain, was detected. In Bombus lapidarius, [D31]-hexadecan-1-ol and [D29]-hexadec-9-en-1-ol were found in the LG. Furthermore, the deuterium labelled precursor was incorporated into triacylglycerols (TAG) of the fat bodies of males. In vitro incubation of the labial glands of Bombus lucorum males with deuterium- and 13C-labelled palmitic acid led to the formation of saturated ethyl esters only.
Observed metabolites of [D31]-hexadecanoic acid injected in Bombus lucorum males
In vitro incubations Dissected labial glands of Bombus lucorum males were incubated with [D31]-hexadecanoic acid, [D5]-ethanol, and [13C16]-hexadecanoic acid, respectively. The following metabolites were identified: ethyl [D31]-hexadecanoate, ethyl [13C16]-hexadecanoate, [D5]-ethyl dodecanoate, and [D5]-ethyl tetradecanoate. No unsaturated metabolites were detected. The time course was followed for 42 days. After 14 days, the amount of esters was no longer increasing.
Time course of the formation of ethyl [13C16]-hexadecanoate in vitro.
Conclusion Our in vivo incubation experiments provide conclusive proof of the presence of species-specific esterases, desaturases and FA reductases in male bumblebees. The in vitro incubation experiments indicate that different steps of the pheromone biosynthesis take place in different parts of the body. By comparison of our findings on bumblebee males with the biosynthetic pathways of periodic production of sex pheromones in female moth, one can see that marking pheromones are produced in much larger quantities. This fact may indicate that bumblebee males use abundant fatty acids deposited in TAG as starting material instead of (or alternatively to) de novo synthesis.
References
Bergström G., Kullenberg B., Ställberg-Stenhagen S.:
Urbanová K.,Valterová I., Hovorka O., Kindl J.:
Calam D.H.:
Research team Anna Luxová, Irena Valterová (Head of the Team), Karel Stránský, Oldřich Hovorka, Aleš Svatoš
Luxová A., Valterová I., Stránský K., Hovorka O., Svatoš A.:
Bumblebees (part I)
Michal Hoskovec © 8.II.2007
|
||||||||||||||||||||||||||||||||||
