Consequences of defoliation on phenological interaction between Epirrita autumnata and its host plant, Mountain Birch

1. Defoliation-induced changes in the budbreak phenology of Mountain Birches ( Betula pubescens ssp. tortuosa (Ledeb.) Nyman), and their effects on herbivore performance, were investigated during an outbreak of the spring-feeding geometrid, Epirrita autumnata (Bkh.).
2. Total defoliation (followed by refoliation) by E. autumnata larvae was required to achieve significant delaying of budbreak of Mountain Birch one year after damage.
3. Delayed budbreak has potentially deleterious effects on herbivore performance. However, E. autumnata larvae show phenotypic responses that increase the synchrony between larvae and leaves: high larval density, a prerequisite for severe defoliation, delays egg hatch in the following year.
4. Late hatching larvae performed as well on birches with delayed budbreak due to the previous year's total defoliation as did early hatching larvae on birches with earlier budbreak.     

Limits to the abundance of rare species: an experimental test with a tree aphid

Abstract. 1. The birch ( Betula )-feeding aphid, Monaphis antennata, is always found at low densities on individual hosts and has low local abundance, but another birch-feeding aphid, Euceraphis betulae , is often found at high densities on individual hosts and has high local abundance.
2. This work attempts to establish whether the interaction between M. antennata and its host or the behaviour of individuals limits its densities.
3. Both species were reared on saplings, and population sizes were monitored for 6 weeks. Two levels of host quality were used and feeding space was kept constant throughout the experiment. Adults were prevented from leaving the saplings by clipping their wings, and predators were excluded.
4. On plants of similar host quality, both species achieved similar population sizes.
5. It is concluded that resource availability or the interactions between individuals are unlikely to be important causes of rarity.