Life cycle regulation in the heather psyllid Strophingia ericae: responsesto temperature and photoperiod

The response of overwintering nymphs of Strophingia ericae (Curtis) (Homopt era: Psylloidea) to long and short photoperiods over a range of temperature s was investigated to determine the interaction between these factors and w inter development as a regulatory mechanism of their hfe cycle. Strophingia ericae was successfully reared from egg to adult in a long phot operiod (LD 18:6h) at 10, 15 and 20 degrees C on its host plans Calluna vul garis. Although development time was longer at 10 than at 15 or 20 degrees C(approximate to 263 days compared with approximate to 155 and approximate to 159 days, respectively), there was no interruption in development at any of these temperatures, indicating that there was no obligatory diapause. H owever, short photoperiod (LD 12:12 h) inhibited development of overwinteri ng fifth instars collected from the field in early winter. Those collected in September and kept at 15 degrees C developed to adult in approximate to 120 days in a short photoperiod (LD 12:12 h) compared with approximate to 4 0 days in a long photoperiod (LD 18:6 h). Inhibition became weaker in Decem ber and disappeared by January, when fifth instars developed to adult at th e same rate in both long and short photoperiods ( approximate to 30 days). A similar photoperiodic response was observed when the experiment was repea ted at 10 degrees C, although development times were consistently longer. T he observation that insects collected from the field in early winter were a ble to resume development immediately: on transfer to favourable conditions (15 degrees C and LD 18:6 h photocycle) suggests that there is a photoperi odically induced quiescence (rather than a true diapause) in overwintering S. ericae, which becomes progressively reduced as winter proceeds. It was concluded that the life cycle of the upland and possibly the lowland form. of S. ericae is regulated by a winter-active photoperiodic inhibitio n of development, which effectively synchronizes the emergence of the adult stage with higher spring temperatures and renewed host plant growth.