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

Abstract .The response of overwintering nymphs of Strophingia ericae (Curtis) (Homoptera: Psylloidea) to long and short photoperiods over a range of temperatures was investigated to determine the interaction between these factors and winter development as a regulatory mechanism of their life cycle. Strophingia ericae was successfully reared from egg to adult in a long photoperiod (LD 18:6 h) at 10, 15 and 20°C on its host plant Calluna vulgaris. Although development time was longer at 10 than at 15 or 20°C (≈ 263 days compared with ≈ 155 and ≈ 159 days, respectively), there was no interruption in development at any of these temperatures, indicating that there was no obligatory diapause. However, short photoperiod (LD 12:12 h) inhibited development of overwintering fifth instars collected from the field in early winter. Those collected in September and kept at 15°C developed to adult in ≈ 120 days in a short photoperiod (LD 12:12 h) compared with ≈ 40 days in a long photoperiod (LD 18:6 h). Inhibition became weaker in December and disappeared by January, when fifth instars developed to adult at the same rate in both long and short photoperiods (≈ 30 days). A similar photoperiodic response was observed when the experiment was repeated at 10°C, although development times were consistently longer. The observation that insects collected from the field in early winter were able to resume development immediately on transfer to favourable conditions (15°C and LD 18:6 h photocycle) suggests that there is a photoperiodically 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 inhibition of development, which effectively synchronizes the emergence of the adult stage with higher spring temperatures and renewed host plant growth.