Effects of synchronization with host plant phenology occur early in the larval development of a spring folivore

Early spring feeding Lepidoptera depend on synchronization of larval emergence with host plant phenology for optimal growth and development. Physical and chemical characteristics of foliage change over the course of the growing season, and a delay in larval emergence therefore results in larvae foraging on lower quality food. We examine the effect of synchronization of larval emergence with leaf phenology on the entire larval stage of the forest tent caterpillar, Malacosoma disstria Hubner, 1820 (Lepidoptera: Lasiocampidae). Caterpillars were reared from egg hatch to pupation on trembling aspen, Populus tremuloides Michx; 10 days separated egg hatch in the early and late treatments. Late-hatching caterpillars experienced reduced growth in the early instars, but growth in the later instars did not differ between treatments. Reduced growth early in development resulted in both prolongation of the larval stage through the occurrence of additional instars, and lower pupal mass. Aspen foliage quality changes rapidly during leaf expansion, and the late-hatching caterpillars likely missed the narrow window of opportunity for young larvae to feed on high-quality developing foliage. This study demonstrates the importance of early-instar ecology in Lepidoptera.