Seasonality of a tropical leaf-mining moth: leaf availability versus enemy-free space

1. Natural enemies may determine the seasonal occurrence of insect herbivores by restricting the presence of their vulnerable life-stages to periods of low natural enemy activity. 2. A tropical leaf-mining moth, Bucculatrix sp., feeding on the understorey plant Forsteronia spicata, normally occurs only in the early-wet season in the tropical dry forests of Costa Rica, this period coinciding with a time when natural enemy activity is thought to be lowest and when young leaves are most abundant. 3. A manipulative experiment was run to establish whether the Bucculatrix sp. can undergo another generation in the late-wet season if suitable leaves are present. If the restricted phenology of this species is due to predator avoidance, then its larvae should experience elevated levels of mortality during this late-wet season generation. 4. An artificial second flush of young leaves was induced on F. spicata by stripping them of leaves after the natural first flush of leaves. Bucculatrix sp. larvae were found on the plants induced to flush but none were found on natural plants. No significant difference in pre-adult mortality was found between the larvae on the natural early-wet season and the artificial late-wet season leaves. 5. The primary factor restricting the seasonal occurrence of Bucculatrix sp. is concluded to be the availability of suitable leaves and there is no evidence to suggest that natural enemies play a role in determining its phenology.