Induced remanent magnetization of social insects

The induced remanent magnetization (IRM) of honeybees Apis mellifera and an ts as Pachycandyla marginata, a migratory species, and Solenopsis sp., a fi re ant, was obtained using a SQUID magnetometer from 10 to 300 K. An anomal ous sharp change of the remanent magnetization is observed at 67 +/-0.2 K f or migratory ants. The IRM at room temperature indicates the presence of at least 10 times lower concentration of magnetic material in the whole fire ant as compared to the migratory ant abdomen (0.22 +/-0.33 x 10(-6) emu/ant , and 2.8 +/-1.2 x 10(-6) emu/abdomen, respectively). Our results in honeyb ee abdomen (4.6 +/-0.9 x 10(-6) emu/abdomen) agree with other reported valu es. IRM at room temperature in ants and honeybees indicates the presence of single domain (SD) or aggregates of magnetite nanoparticles. The loss of r emanence, from 77 to 300K can be related to the stable-superparamagnetic (S PM) transition of small particles (less than ca. 30 nm). From these values and considering their estimated volumes an upper limit 10(10) SPM and 10(9) SD or aggregate particles are obtained in these insects. (C) 2001 Elsevier Science B.V. All rights reserved.