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 p roven to be an adaptive character for insects like locusts. Observatio ns made on a cohort of Brevipalpus phoenicis (Geijskes) in groups of 5 0 individuals revealed that grouping shortens the developmental time a nd total life span and reduces the capacity for oviposition. This enab les one to postulate a new hypothesis that during an epidemic outbreak and in the initial phase of colonisation the mites live longer and pr oduce 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 populatio n is higher, the mites develop faster before the available food is exh austed.