Predicting responses to climate change: the effect of altitude and latitude on the phenology of the Spittlebug Neophilaenus lineatus

1. The phenology of Neophilaenus lineatus (Homoptera: Cercopidae) was studi ed along altitudinal and latitudinal transects in the UK. The response of t he life cycle to these existing temperature gradients has been used to pred ict the likely effects of future climatic warming. 2. The date of spring egg hatch varied by a maximum of 4 weeks across the a ltitudinal gradient (440 m) and by 2 weeks in different years of the study. Autumn and winter temperatures do not determine hatching date because the eggs are in diapause during this period. It is only when the eggs terminate diapause in early spring that temperature differences between years and al titudes (or as a result of climatic warming) start to affect the date of eg g hatch. 3. The delayed egg hatching with increasing altitude meant that the start o f nymphal development was later at higher altitudes, The development rate o f nymphs at higher altitudes was not significantly different from that at l ower altitudes because the altitudinal lag in temperature was partially com pensated for by the more advanced state of the season. Annual differences i n spring and summer temperatures resulted in variations in nymphal developm ent rate between years, with a 1 degrees C temperature rise shortening nymp hal development by 3.5 days. 4, The appearance of adults was delayed by 5.6 days for every 100 m increas e in altitude, largely as a consequence of the later egg hatch at higher al titudes. The later appearance of the adults at higher altitudes and in cold er years, reduces the length of the potential oviposition period as females are killed by autumn frosts. Climatic warming would expand the length of t he oviposition period and thus increase the upper altitude limits of N. lin eatus. 5. A 4.5 degrees latitude difference within the UK appeared to have little effect on the timing of development in N. lineatus, possibly as a result of a geographical dine in temperature or photoperiod response. 6. Annual insects, such as N. lineatus, are likely to show a relatively sma ll geographical displacement as a consequence of climatic warming. This is because of the temperature mitigating responses of diapause and the relativ e stability of the length of the development period over wide altitudinal a nd latitudinal ranges.