INDUCTION OF WINGED SEXUPARAE IN ROOT-INHABITING COLONIES OF THE APHID PEMPHIGUS-BETAE

Growth chamber experiments were conducted to determine what environmen tal factors induce the development of sexuparae in root-feeding coloni es of the aphid Pemphigus betae Doane (Aphididae: Pemphiginae). Experi mental colonies were derived from clones that had been reproducing for at least 15 months under constant laboratory conditions. At constant 20-23-degrees-C, sexuparae were almost never produced regardless of th e level of crowding or photoperiod. In contrast, every culture of seve ral clones produced sexuparae when subjected to temperatures alternati ng between 20 and 15-degrees-C during the light and dark phases respec tively. This fluctuating temperature regime resulted in sexupara produ ction regardless of photoperiod. All cultures also produced some sexup arae when cultures were kept in constant darkness at temperatures that were either alternated between 20 and 15-degrees-C or kept constant a t 15-degrees-C. Constant 17-degrees-C resulted in sexupara production in most cultures. At 17-degrees-C, experimental manipulation of densit ies within cultures showed that crowding promotes sexupara production. Thus, within the range of conditions occurring at the time of sexupar a induction in the field, photoperiod has no effect on sexupara produc tion, temperature below a threshold between 17 and 20-23-degrees-C tri ggers sexupara production, and crowding promotes sexupara production b ut only if temperature is low enough.