Magnetic material in migratory and non-migratory Neotropical Lepidoptera: a Magnetic Resonance study

Abstract Many animals use the geomagnetic field to orient. Among the mechanisms proposed for magnetoreception, the ferromagnetic hypothesis assumes a magnetosensor based on magnetic particles. In this study, magnetic resonance (MR) is applied to 11 Lepidoptera species separated into four body parts: antennae, head, thorax, and abdomen. For the first time, magnetic characteristics of the parts are compared between migratory Urania fulgens and Aphrissa. statira and non-migratory Heliconius ethilla, Anartia amathea, An. fatima and Actinote thalia, species for which we had sufficient specimens for statistical analyses. Spectral characteristics of the magnetic material include the geff factor, linewidth and the high field (HF) component area, as well as, the HF area ratio of these body parts. The broad HF and low field (LF) components, commonly observed in social insect spectra, are present in the Lepidoptera body part spectra. Other unusual narrow lines are superimposed mainly to the HF component, the narrow component at geff ∼2.05 associated with very small Fe aggregates and the extra component at geff values from 2.13 to 3.03. The relative amount of magnetic material in the body parts are derived from the HF area. The results indicate that only antenna/head ratio of magnetic material amount and the spectral components distinguish migrant from non-migratory Lepidoptera. The extra component showing angular dependence and previously observed in spectra of honeybee abdomens and leaf-cutter ant antennae was observed in the antennae of non-migratory species but not in the migratory ones. Similarities of these attributes with other homing insects suggest that global orientation is as important for butterflies that occupy home ranges, defend territories, and trap-line flowers as it is for long-distance migrating Lepidoptera.