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

Ferromagnetic Resonance (FMR) and SQUID magnetometry were used to study Solenopsis interrupta ants at room temperature. Nest was collected and kept in the laboratory. Ants coming back to the nest carrying food were collected and freshly separated in head with antennae, abdomen and thorax. Twenty units of each body part were measured by SQUID and FMR, after twelve days and one month respectively. Fresh head with antennae hysteresis curves repeated 45 days after preparation, presented a decrease of the saturation magnetization (JS), by ~1/4, which motivated fixing samples in glutaraldehyde. Similarly two other series were prepared after about 2.5 months in the laboratory nest, and kept in glutaraldehyde 2.5 % in 0.1 M sodium cacodylate buffer pH 7.4 (GC buffer). The ferrimagnetic broad lines associated to magnetite/maghemite isolated nanoparticles (high field, HF) and to large nanoparticles or aggregates (low field, LF) in insect spectra are also observed in the S interrupta body part spectra, although they slightly differ in resonant fields and lineshapes. The saturation (Js) and remanent (Jr) magnetizations and the coercivity field (Hc) were obtained from the hysteresis curves. The absorption spectrum areas, proportional to the magnetic material amount, S and Js were used to calculate the relative amount of this material in each body part (Table 1). The total Js of the sample in glutaraldehyde is about 1/2 of the fresh one, although this difference is not observed from the FMR data. The freshly prepared thorax spectra and hysteresis curve are below the both techniques sensitivity. The highest magnetic material fraction was found in the S interrupta head with antennae (table 1), as previously observed in S substituta ants and some other social insects. Those differences can be related to sample preparation or to diet days, seasonality, etc. Further experiments are necessary to establish the best methodology to study magnetic material in social insects. Solenopsis ants are easily found and are widely spread in Brazil. The similar results between species (S. substituta and S. interrupta) point to the possibility of systematizing the study of magnetic material in this genus. Sample Head with antennae fresh Abdomen fresh Head with antennae GC buffer Abdomens GC buffer Thorax GC buffer Absorption area, S (a.u.) 5.3 x 109 2.4 x 109 5.2 x 109 1.5 x 109 2.2 x 109 Percentage from S 70% 30% 58% 17% 25% JS (x10-5 emu) (2.9 „b 0.3) (2.7 „b 0.1) (1.6 „b 0.4) (0.52 „b 0.16) (0.31 „b 0.04) JR (x10-6 emu) (7.5 „b 0.9) (3.9 „b 0.4) (1.3 „b 0.5) (0.53 „b 0.04) (0.19 „b 0.04) HC (Oe) 40 „b 5 70 „b 5 31 „b 5 83 „b 8 83 „b 2 Percentage from JS 52% 48% 66% 21% 13%