Barro Colorado Island at the crossroads: Trans-isthmian insect migrations

Authors: Srygley, Robert; OLIVEIRA, EVANDRO - Smithsonian Tropical Research; RIVEROS, ANDRE - Universidad Del Rosario, Columbia; DUDLEY, ROBERT - University Of California

Submitted to: Smithsonian Contributions to Botany
Publication Type: Book / Chapter
Publication Acceptance Date: 11/27/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Animal migration is an expensive undertaking in both energy consumed and time invested. Yet we know little about where animals move, how they orient, or why they migrate. We investigated migrations of butterflies, moths, and dragonflies in Panama to answer three broad questions: where do the insects migrate, how do they orient, and why do they migrate. We focused on the Sulphur butterfly Aphrissa statira and the Daggerwing butterfly Marpesia chiron, the day-flying moth Urania fulgens, and the globe-trotter Pantala flavescens in particular. Butterfly migrate across the isthmus of Panama from the Atlantic coastal wet forest to the Pacific coastal dry forest in May-July of each year. The butterflies maintain a preferred orientation with a sun compass, and they are able to adjust their headings to compensate for drifting off-course even when flying over water. Butterflies and dragonflies adjust their speed to maximize the range that they can fly on a given amount of fuel. In contrast, the day-flying moth does not compensate for crosswind drift or adjust its speed to economize fuel when flying over water. More butterflies migrate during El Niño events when host plants produce more leaves. Understanding mechanisms of insect migrations improves prediction of population movements of insect pests and pollinators.

Technical Abstract: Butterflies cross the isthmus of Panama in abundance during the early rain season (May-July). The migratory flyway extends from the Atlantic to the Pacific coasts of Panama and may include the Caribbean coast of Colombia. Butterflies use a time-compensated sun compass to maintain their preferred orientation over long distances, and when crossing the Panama Canal at BCI, also use local landmarks to correct for wind drift. Butterflies and dragonflies (but not the day-flying moth Urania fulgens) adaptively adjust their speed to economize fuel and maximize the range of their migration. In Panama, El Niño is a major driver of butterfly migrations across the isthmus. More pronounced dry seasons associated with El Niño events promote host plant leaf flushing, egg laying by butterflies on new leaves, and expansion of migratory butterfly populations.