Field Study of the Mobility of Oribatei (Acari), Using Radioactive Tagging

Abstract

To some extent, it is possible to check the validity of these hypotheses by following the movements of individuals in the field. Taking into account 'the size of the animals, the only practicable method for this purpose is by radioactive tagging. After labelling, the animals are returned to the field and their daily movements are observed with a Geiger counter. Two methods were used to label the animals. The first, proposed by Davis & Nagel (1956) consists of immersing the individuals in a radioactive solution, by ion exchange, some radioactive salts remain on the cuticle. The animals were immersed three to six times for 1 min every 2 h in a solution of Na2Ir192Cl6 (2 mc/ml) or of Sc46Cl (8 mc/ml). One day after the last immersion, the animals were washed in distilled water, to remove any salt not fully bound on the cuticle. Generally, forty animals were treated simultaneously and at the end of the labelling, twenty were selected whose radioactive level was adequate for detection in the field. Unfortunately, this simple method does not suit many Oribatids, most of which have an unwettable cuticle. For such animals, I used a different method consisting of mixing a small amount (250 nrc) of Ce144Cl in a little Students' oil Colour, and putting a tiny drop of this paint on the hysterosoma. Cerium-144 is an isotope with quite a long half-life, and gives by disintegration a daughter isotope, Praseodymium-144, which is a very strong beta emitter. Thus, the detection of the animals is easy with a Geiger-Muller tube (laboratory portable monitor M.B.L.E., PN 282/A equipped with a Geiger tube, ASDAM 18505). The amount of radioactive material that was used for these experiments was 10 mc of iridium, 40 mc of scandium and twice 5 mc of cerium. The radioactivity of these solutions was sufficiently high to require the precautions usually associated with a properly equipped radioisotope laboratory (lead bricks, laboratory monitor, pocket dose-meter .) and a special training of the experimenter.