350. WE-Heraeus-Seminar /Biophysics of Magnetic Orientation in Animals

Magnetoreception in social insects is still poorly understand. The ferromagnetic hypothesis, proposing biomineralized magnetic nanoparticle system as the magnetic field detector, is well accepted. Evidence of magnetite/maghemite nanoparticles in the migratory ant, Pachycondyla marginata obtained by transmission electronmicroscopy (1) stimulated the magnetic characterization of these materials in the body parts of other social insects, by SQUID magnetometry and ferromagnetic resonance (FMR) (2-5). Particularly interesting is the highest magnetic material fraction (42 „b 3%) in this ant antennae and 66 „b 6% in head with antennae. This sensory part, functioning primarily as an organ of touch, could also be a magnetosensor one. Under this point of view, the room temperature hysteresis curves and FMR spectra of the body parts of a fire ant, Solenopsis interrupta (S. i.) and a stingless bee, Schwarziana quadripunctata (S. q.) were studied. From the magnetisation saturation values, 66 „b 2% and 67 „b 7% of the magnetic material was found in the head with antennae of S. i. and S. q., respectively, with 44 „b 4% coming from the S. q. antennae. Confirming the higher magnetic amount in these head with antennae insects, the second integral of the derivative FMR spectra yields values of 58 „b 2 % and 67 „b 4% in the of S. i. and S. q., respectively. The very similar values in the three insects is strickly interesting and deserves further experiments comprising other social insect species. 1. D Acosta-Avalos et al. J. Exp. Biol. 202(19) (1999) 2687-92 2. DMS Esquivel et al. BioMetals 17 (4): 467-470, 2004 3. LJ El-Jaick et al. Eur Biophys J 29 (2001) 579-586 4. E Wajnberg et al. Biophys J 78(2) (2000) 1018-23 5. E Wajnberg et al. J. Magn Magn Mat 226-230 (2001) 2040-1 keywords: antenna, magnetite, magnetosensor