Diel periodicity of emergence of adult citrus rust mites in central Florida

Emergence of adult citrus rust mites, Phyllocoptruta oleivora (Ashmead) from the imagochrysalis occurred with a diel periodicity that peaked between mid morning and early afternoon. The pattern of emergence did not differ for mites reared from eggs held under different photoperiod regimes. The transition of nymphs to the imagochrysalis stage also showed a diel periodicity, occurring in the evening. The average duration of the imagochrysalis stage at 28 degrees C was 14-15 h. Wetting by rain or dew was simulated by immersing fruit in water each night, but the transition to the imagochrysalis stage or the subsequent emergence pattern of adults was not affected. Adult mites reared from eggs laid during two, consecutive 12-h periods emerged at the same time of day, but the peaks of emergence were separated by 24 h. Eclosion of larvae from eggs laid during two, consecutive 12-h periods did not show a diel periodicity. Eggs continuously immersed in water during their development did not hatch, whereas there was a small, but significant, reduction in the viability of eggs immersed in water each night. These results are discussed in relation to external cues that may entrain the diel patterns of development and adult emergence, and to the adaptive responses of citrus rust mite to cyclic fluctuations of key environmental variables in central Florida.