Sensory basis of lepidopteran migration: focus on the monarch butterfly

- Monarch butterflies are a model system for studying long-distance migration.
- Monarchs use a bidirectional time-compensated sun compass for orientation.
- Monarchs exploit a light-dependent inclination magnetic compass for orientation.
- The antennae provide key sensory mechanisms for orientation during migration.
- Environmental pollution can disrupt orientation mechanisms.

In response to seasonal habitats, migratory lepidopterans, exemplified by the monarch butterfly, have evolved migration to deal with dynamic conditions. During migration, monarchs use orientation mechanisms, exploiting a time-compensated sun compass and a light-sensitive inclination magnetic compass to facilitate fall migration south. The sun compass is bidirectional with overwintering coldness triggering the change in orientation direction for remigration northward in the spring. The timing of the remigration and milkweed emergence in the southern US have co-evolved for propagation of the migration. Current research is uncovering the anatomical and molecular substrates that underlie migratory-relevant sensory mechanisms with the antennae being critical components. Orientation mechanisms may be detrimentally affected by environmental factors such as climate change and sensory interference from human-generated sources.