The role of pheromones in insect behaviour and ecology

Abstract

Primer pheromones may act upon sexual maturation of adult insects (as in the honey bee, Chapter 1) or on development. In locusts both kinds of effect occur. At low densities the desert locust, Schistocerca gregaria, is cryptically coloured, but in high densities the insects undergo a startling colour change and they aggregate, sometimes forming swarms of hundreds of millions of insects. This phase change involves graded changes in colour, morphology, behaviour and physiology. Crowding of hoppers is one factor that leads to gregarization as a result of the experience of increased tactile stimulation (Ellis, 1959). The existence of a gregarization pheromone has been demonstrated in nymphal faeces, changing behaviour and colour in seven days (Gillett, 1983). Exposure to adult faeces, on the other hand, leads to solitary behaviour within four days without affecting colour. There has been controversy over the chemical nature of the gregarization pheromone, but Fuzeau-Braesch et al. (1988) found that the air from around gregarious Locusta migratoria and Schistocerca gregaria was rich in phenol, guaiacol and veratrole. A mixture of these three compounds causes locusts to aggregate and they may be part of the gregarization pheromone, which produces a ‘cohesive’ effect.