Intake and possible transfer of lipid by the post‐pharyngeal glands of Atta cephalotes L

The paired post-pharyngeal glands of ants open directly into the pharynx (Pavan & Ronchetti , 1955). Each gland consists of a proximal sac-like port ion and a distal region of several digit-like extensions. In the leaf-cutting, fungus-growing ant Atta cephalotes (L.), the glands usually contain a yellow oil, the amount of which differs between individuals. Echols (1966) was the first to observe that in leaf-cutting ants fed with soya bean oil dyed with Calco oil blue, these glands became coloured within 15 hours of feeding. Echols ' experiments have been repeated recently (Percy, 1970) and several new points have emerged. The rate of entry of soya bean oil dyed with Sudan III is such that a gland becomes coloured within 3 minutes of application. Fat-soluble dyes, e.g. Sudan III and Calco oil red, accumulate in the gland lumen with a smaller propor t ion of dye of the reaching the gut. The fat and water-soluble dye, Nile blue, entered the gland to a lesser extent and was mainly confined to the gut. The water-soluble methylene blue never penetrated far into the postpharyngeal glands but sometimes it was seen at the base of the gland close to the opening into the pharynx. When this occurred the boundary between the blue-dyed area and the clear yellow oil of the gland was a sharp line which suggested an interface between immiscible liquids. Methylene blue was found in quanti ty throughout the gut. When Mirex (dodecachloroetahydro-l ,3,4-metheno-2H-cyclobuta(cd) pentalene) a stomach poison extensively used in ant control (Lofgren et al., 1964), or aldrin are dissolved in soya bean oil they accumulate in the gland in a similar way to Sudan IIf. The accumulation of soya bean oil containing either dye or insecticide is most probably explained in terms of mass flow into the gland. However, a possible objection to this explanation is that the solutes might diffuse at a greater rate than the oil solvent. To overcome this objection, prel iminary experiments using radiolabelled soya bean oil have been made and the results are summarized here. Glyceryl tristearate is a normal component of soya bean oil. The 14C isotope of this triglyeeride was added to the oil to give a concentrat ion of 250 #C/ml. Medium-sized Atta workers were used and standard amounts of labelled oil were placed on the mouthpar ts of the experimental insects. After 5 minutes the post-pharyngeal glands were removed, spotted on planchettes and counted in a Tracerlab proport ional counter. All nine replicates gave a count higher than that of the background produced by the controls. Autoradiography of the whole gland using a simple apposit ion technique confirmed the intake of labelled soya bean oil by the post-pharyngeal gland. This evidence makes it reasonable to assume that the dye or the insecticide enters the gland by a similar process to that of the oil fed to the ant. Some naturally occurring oily material is almost certainly produced by the large cells lining the post-pharyngeal glands. It is suggested that the post-pharyngeal glands of Atta serve two functions. 1. The secretion of the gland may serve a nutri t ional role. Atta larvae, for example, are normally fed on clusters of fungal hyphae (Weber, 1966), which are cultured in the nest and perhaps this