Pheromones in the life of insects

Abstract

Life in insect societies asks for a permanent flow of information, often carried by rather simple organic molecules. Some originate from plants as odours of blossoms or exudates from trees. Especially important are the intra- and interspecific combinations of compounds produced by the insects themselves. These are called pheromones or ecto-hormones and serve a variety of tasks. The paper deals mainly with honeybee pheromones, but takes also into consideration those of wasps and hornets. Effects of pheromones are monitored ethologically by direct observation and filming as well as in a more quantitative manner with using direct and indirect calorimetry. In all experimental set-ups alarm pheromones were used as controls. They show an up to fourfold increase of activity after a few seconds, determined for small groups of insects as well as for a whole hornet nest placed in a 25-l calorimeter. A variety of cosmetics like soaps, shampoos, lotions and perfumes are included in the investigations because of repeated reports about unwarranted insect attacks which are said to be provoked by such products. None of the applied substances provoked a significant reaction of the bees (p > 0.05). A short appendix discusses the still questionable existence of pheromones in man, which were confirmed under laboratory conditions, but not yet for daily life.

Appendix 1

With respect to pheromones, the question often arises if pheromones—which are known from unicellular yeast cells up to all classes of animals—do exist for humans too. This question is still under discussion with many hints that pheromones are important for humans also, mainly in a sociosexual context (Hatt 2004; Wysocki and Preti 2004; Shepherd 2006). After an early rather vague discussion in the book of Agosta (1992) more recent reviews (Kohl et al. 2001; Grammer et al. 2005; Fink and Sövegjarto 2006) present different aspects of their origin, detection and effects. Human apocrine glands are supposed to be the main producer of pheromones. They are located in the axillae pits and the pubic region. The fact that a functional vomeronasal organ directly connected with the limbic system exists in humans also supports the idea of pheromone activities (Monti-Bloch et al. 1998).

Axons of the receptor cells in the vomeronasal organ directly lead to the bulbus olfactorius which projects into the limbic system. Thus, the information may be received unnoticed by us. Whether the pheromones may act along this line is still discussed (Fink and Sövegjarto 2006). Nevertheless, Grammer and colleagues wrote that “human sociosexual interactions are influenced by pheromones, even if they cannot be detected consciously” (Grammer et al. 2005).

The androstenol-androstenone-signalling system is a special focus of research. It was concluded that “… the model of humans being primarily visual creatures may require some reconsideration. Human life and interactions are influenced by pheromones whether or not affect or effect is part of our consciousness.” and “Human pheromones have more potential than any other social environmental sensory stimuli to influence physiology and, therefore, behaviour.” (Kohl et al. 2001). Nevertheless, doubts still exist because convincing results were only obtained under laboratory conditions until now, but not in real life. It needs carefully chosen experimental conditions to detect a—presumably weak—influence of human pheromones and body odour on the sociosexual behaviour and to prove efficacy of the commercial so-called sexual attractants (Fink and Sövegjarto 2006).