MASS TAGGING OF BLACK FLIES (Diptera: Simuliidae) WITH RADIOPHOSPHORUS

Abstract

A new method for tagging large numbers of black flies (Simulium spp.) for flight range investigations is described. Radioactive adults that were readily detected with a Geiger counter were reared from larvae that had been kept for 24 hr. in a very dilute solution of radioactive phosphorus (0.2 μc. per ml.) and then returned to nonradioactive water to complete their development. The treatment did not visibly harm larvae or the adults that emerged from them. Larvae were reared in small containers of water circulated and aerated with air jets in the laboratory, and with a simple arrangement of stream-driven paddle wheels in the field. By this method, tagged larvae, pupae, and adults were produced which could be readily detected with a Geiger counter. In field tests, tagged larvae and pupae were found as far as 520 yd. downstream from the point of release. Tagged adults were taken in cages placed over radioactive larvae and pupae in the stream, but only one was recaptured in the open, and this only 100 yd. from the stream. Failure to capture more tagged adults was believed due mainly to inadequate collecting methods. A short treatment period is desirable when tagging large populations of black-fly larvae in the field because other methods, such as rearing in a small container for a long period of time, or treating the stream with a radioactive isotope, are impractical. This method would be applicable in studies on dispersal and predation of immature and adult stages of other insects of streams and ponds.