Byers, J.A. 1991d. Pheromones and chemical ecology of
locusts. Biological Reviews 66:347-378.
Abstract--
Modern studies of chemical ecology and behaviour of the locusts
Schistocerca gregaria and Locusta migratoria (Orthoptera: Acrididae) 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) behavior 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 long-
range sex pheromone, sex-recognition pheromone, grass odours and
feeding stimulants and deterrants. 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.
Chemical Ecology