Phase variation—a possible adaptive character for the false spider mite, Brevipalpus phoenicis (Geijskes 1939)

The phenomenon of phase variation brought about by crowding has been proven to be an adaptive character for insects like locusts. Observations made on a cohort of Brevipalpus phoenicis (Geijskes) in groups of 50 individuals revealed that grouping shortens the developmental time and total life span and reduces the capacity for oviposition. This enables one to postulate a new hypothesis that during an epidemic outbreak and in the initial phase of colonisation the mites live longer and produce more eggs when the density of the population is lower until the population reaches a threshold level of crowding and vice versa. This phenomenon of phase variation brought about by the group effect is an adaptive character in the sense that when the density of the population is higher, the mites develop faster before the available food is exhausted.