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Chemical analyses revealed that in Cataylyphis niger both the hemolymph and the crop contain the same hydrocarbons that are found in the postpharyngeal gland (PPG). On the cuticle, on the other hand, alkanes, and in particular nonacosane, were more abundant than in the PPG. Studies of their biosynthesis in vivo, using intact ants, revealed the presence of newly synthesized hydrocarbons in both the PPG and the crop. In decapitated ants (in the absence of the PPG), however, the crop did not contain any newly synthesized hydrocarbons, indicating the PPG as the major source of crop hydrocarbons. The fat body, as demonstrated by in vitro studies, is the major tissue that biosynthesizes hydrocarbons. The PPG failed to do so, but showed good de novo biosynthesis of other lipid constituents. The large amount of hydrocarbons in the crop suggests that the alimentary canal may serve as an outlet for the overflow of PPG hydrocarbons, or as a route for the directed clearance of hydrocarbons from the PPG.

These results confirm and enlarge the model proposed for hydrocarbon circulation in C. niger. They are synthesized by the fat body, released to the hemolymph and transported to the cuticle and the PPG. The PPG hydrocarbons are applied to the cuticle by self-grooming, but can also be cleared via the alimentary canal. Partial emptying of the PPG may facilitate the admiring of recognition cues that the ant may acquire from nestmates by trophallaxis. The reason for the dissimilarity in hydrocarbon composition between the PPG and the cuticle is not yet clear; it may be due to secretions from additional glands, or reflect deviant hydrocarbon transport mechanisms between the PPG and the cuticle. (C) 2000 Elsevier Science Ltd. All rights reserved.