Magnetic material in migratory and non-migratory Neotropical Lepidoptera: A magnetic resonance study

Authors: CAMBRAIA ALVES, ODIVALDO - Fluminense Federal University(UFF); WAJNBERG, ELIANE - Brazilian Center For Physics Research; ESQUIVEL, DARCI - Brazilian Center For Physics Research; Srygley, Robert

Submitted to: Journal of Magnetism and Magnetic Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2020
Publication Date: 5/23/2020
Citation: Cambraia Alves, O., Wajnberg, E., Esquivel, D.M., Srygley, R.B. 2020. Magnetic material in migratory and non-migratory Neotropical Lepidoptera: A magnetic resonance study. Journal of Magnetism and Magnetic Materials. 513:1-11. https://doi.org/10.1016/j.jmmm.2020.167053.
DOI: https://doi.org/10.1016/j.jmmm.2020.167053

Interpretive Summary: Behavioral evidence indicates that at least some insects use the Earth’s geomagnetic field as an orientation cue, but the sensory structures have never been characterized. One hypothesis is the use of iron particles that alter their orientation with the polarity of the field as a part of the magnetic sense. We used ferromagnetic resonance to examine the presence and composition of magnetic particles in the body parts of a migratory butterfly and moth. We compared these species to four that are non-migratory with the expectation that the migratory butterflies would have magnetic components that the non-migratory ones lacked. We compared several aspects of their resonance spectra. The amount of magnetic material in the antenna versus the head differed between migratory and non-migratory species. In addition, an extra line that showed angular dependence and thus is sensitive to its orientation relative to the applied magnetic field also existed in the spectra of the antennae and thoraces of non-migratory species but not migratory ones. Because this extra line was also observed in homing ants and bees, it may be important for insects that, like our non-migratory butterflies, occupy home ranges, defend territories, and trap-line flowers. This research contributes to our understanding of the spatial orientation of insects and is a step closer to characterizing the elusive magnetic compass.

Technical 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, Ferromagnetic resonance (FMR) 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 A. 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 HF area, as well as, the HF area ratio of these body parts. The broad high field (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. Angular dependence and the relative amount of magnetic material are derived from these parameters. The results indicate that only antenna/head ratio of magnetic material amount and the spectral components distinguish migrant from non-migratory Lepidoptera. An extra component (line) showing angular dependence and previously observed in spectra of honeybee abdomens and leaf-cutter ant antennae was frequently observed in the antennae and thorax of non-migratory species but not 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.