Ayres Abstracts
| Ayres, M.P. and S.F. MacLean, Jr. 1987. Development of birch leaves and the growth energetics of Epirrita autumnata (Geometridae). Ecology 68:558-568. |
| Larvae of Epirrita autumnata hatch at the time of budburst, and feed on the immature foliage of mountain birch, Betula pubescens ssp. tortuosa. The effects of leave maturation, temperature, and larval instar on Epirrita growth performance were measured in two seasons. Leaf water, nitrogen, and phosphorus content declined with leaf maturation, while toughness and specific mass increased. There was a sharp decline in larval growth rate attributable to leaf maturation; for example, the relative growth rate of third-instar larvae dropped from 0.52 to 0.11 mg•mg-1•d-1 in 3 d. Consumption rate, digestive efficiency, and nitrogen utilization efficiency declined on mature leaves; assimilation rate and Epirrita growth rate declined as a consequence. The rate of frass production remained very constant. Epirrita consumption rate appeared to be limited by postingestive handling of indigestible leaf tissue. Effects of leaf maturation were greatest at warm temperatures. Third-instar larvae grew faster than later instars on early season leaves, while fifth (last) instar larvae were least sensitive to seasonal effects; differences between instars make them well suited to the leaves that they normally encounter. The phenological constraint imposed by leaf maturation, and exacerbated by Epirrita adaptations that maximize growth rate on young foliage, seems to be an important selective force influencing the duration and timing of larval growth. |
| Betula pubescens/ Epirrita autumnata/ Finland/ growth energetics/ herbivore adaptation/ instar/ Lapland/ larval growth/ leaf development/ phenology |