Ontogeny of the fine structure of the mandibular glands of the honeybee (Apis mellifera L.) workers and the pheromonal activity of 2-heptanone

Abstract

In the present study we have tried to: (1) correlate, according to the age and polyethism of worker bees, the ontogeny of their mandibular glands and the age-dependent changes of 2-heptanone levels and (2) evaluate the role of 2-heptanone in some social behavioural interactions of the honeybee. 1. (1) Each mandibular gland of the worker honeybee, Apis mellifera (Hymenoptera: Apidae), consists of an axial cavity lined with a thin cuticular intima elaborated by a flat epithelium, and of numerous glandular units (type 3), each with a duct cell and a large polyploid glandular cell. Mitochondria and endoplasmic reticulum are preponderant organelles. The Golgi apparatus is reduced; its activity is lysosomal. With increasing age, the size of the gland and the amount of 2-heptanone per headspace sample progressively increased. The increasing quantity of 2-heptanone from 0.1 μl at emergence to 7 μl in foraging bees, is strictly correlated with hypertrophy of the mitochondria, which are engaged in the production of heterogeneous bodies. 2. (2) Similar age-dependent changes of 2-heptanone levels were found in mandibular glands of workers from docile and aggressive colonies and the amount of 2-heptanone in foraging bees of the two groups was alike. Neither crushed glands nor 2-heptanone showed any direct effect as an alarm pheromone on guardian bees at hive entrances. 2-heptanone had either an attractive or a repulsive effect on guards, according to the season; it showed a repulsive effect when added to sucrose solution which was visited by foragers. 2-heptanone had a temporary, repulsive effect on the visitation of flowers by foraging bees, hence it seems to act as a "forage-marking" pheromone. 2-heptanone does not inhibit the germination of pollen grains. © 1991.