EFFECTS OF TEMPERATURE ON PHENOLOGICAL SYNCHRONY AND ALTITUDINAL DISTRIBUTION OF JUMPING PLANT LICE (HEMIPTERA, PSYLLOIDEA) ON DWARF WILLOW (SALIX LAPPONUM) IN NORWAY

1. The geographical distributions of three species of jumping plant lice (psyllids) along an altitudinal transect (988-1300 m a.s.l.) in southern Norway were restricted within the range of their host plant Salix lapponum. One species, Cacopsylla propinqua, occurred at all sampling locations between 988 and 1222 m, whereas C.palmeni was confined to higher altitudes (1153-1222 m) and C.brunneipennis was more abundant at lower altitudes (988-1101 m). 2. C.brunneipennis and C.palmeni developed only on female catkins. Development times of catkins and psyllids were similar (approximately 50 days) and successful psyllid development depended on close phenological synchrony with catkins. 3. Thermal requirements for development of female catkins were greater at low altitude (988 m) compared with higher altitude (1222 m), showing local adaptation of S. lapponum to altitude. In general, thermal requirements of psyllids were less than those of catkins at the same location. C.brunneipennis had higher thermal requirements than C.palmeni. 4. Field experiments, using polythene enclosures to elevate temperatures at two sites at different altitudes (by 0.6-1.4 deg. C), showed that insects had an enhanced relative rate of development under elevated temperatures compared with their host plants. 5. Indices of phenological synchrony were calculated from thermal requirements of psyllids and catkins. Under elevated temperatures, phenological synchrony decreased at both sites. This resulted in the subsequent development of smaller adult insects at low altitude, although at higher altitude, insects developing under elevated temperatures were larger and had a higher survival rate compared with controls. 6. Effects of temperature on phenological synchrony may explain the limits to the geographical range of psyllids. The consequences of climate change on psyllid populations will depend on the effects of decreased phenological synchrony on insect development and this may differ within the insect's geographical range.