PHEROMONES AND CHEMICAL ECOLOGY OF LOCUSTS
Authors: BYERS JOHN A. 
Published: January 2008

Modern studies of chemical ecology and behaviour of the locusts Schistocerca gregaria and Locusta migratoria in the laboratory need to be more closely coupled with field experiments and observations. The life history relating to oviposition, transformation to gregarious phases, and adult maturation mediated by pheromones is reviewed. The principles of pheromone isolation and identification are discussed. The long‐term effects of the gregarization pheromone on the physiology are presented, with discussion of morphological changes, chiasma frequency increases, and synchronization of moulting induced by the pheromone. Isolation of the purported gregarization pheromone, locustol, from faeces is discussed in regard to inconsistent effects. Other more immediate effects of the pheromone on the social (gregarious) behaviour and the isolation of possible pheromone components different from but related to locustol are presented. It is stressed that more rigorous isolation studies should be undertaken to resolve conflicting reports and methodological problems. The possibility of an anti‐gregarization pheromone or solitarizing pheromone is discounted. The source and biosynthesis of locustol (or gregarization pheromone) from degradation of lignin by symbiotic bacteria is discussed. Theories of reception of the gregarization pheromone such as inhalation through the spiracles or sensory perception by the antennae are presented. Also an internal mechanism involving cAMP and/or corpora allata may be induced by gregarization pheromone to effect the physiological phase changes. The advantages to an individual of reception of the gregarization pheromone from a group of gregarious and pre‐migrating locusts is discussed. Also the possible benefits of gregarious behaviour, phase polymorphism and migration are dealt with.

An adult (sexual) maturation pheromone has long‐term effects on reducing the period of maturation, and immediate effects on the behavioural vibration response. The epidermal source of the pheromone and glandular cells responsible for the production of the pheromone are discussed. The reception and internal mechanisms of response via the corpora allata are mentioned. The benefits to individuals of synchronized and rapid adult maturation in a gregarious group are considered.

An oviposition‐stimulating pheromone produced by the male accessory reproductive glands appears to be a proteinaceous substance of large molecular weight. On the other hand, an oviposition‐aggregating pheromone volatilizes from epidermal areas of either sex and causes higher oviposition rates in the area of release. The behavioural and ecological aspects of this pheromone are discussed. Several other possible pheromones and semiochemicals are discussed, such as a long‐range sex pheromone, sex‐recognition pheromone, grass odours and feeding stimulants and deterrents. Several possible control strategies using locust pheromones are considered. The general conclusion is that the chemical isolation of the various pheromones is necessary before further progress can be achieved on the source and biosynthesis of pheromone, reception of pheromone, behavioural effects of pheromone, and control measures.