EFFECT OF GAMMA RAYS AND/OR FLUORESCENT PIGMENTS ON STERILITY AND SURVIVAL

Comparative studies on the relative effectiveness of two "Co irradiators differing only in dose rate showed that both were equally effective in producing sterility in the stable fly Stomoxys calcitrans (L.). Survival was superior, however, in those flies irradiated with the higher dose rate unit. Marking with fluorescent pigments produced an increase in daily mortalities regardless of whether or not the flies had been irradiated. It has been demonstrated on numerous occasions that the stable fly, Stomoxys calcitrans (L.), can be controlled with sterile-male releases (LaBrecque et al. 1972, 1975a). However, despite inundative releases, native flies were always in evidence, and their presence was usually attributed to infiltration from adjacent breeding sites. An island-wide pilot study was initiated on St. Croix, U.S. Virgin Islands, in the summer of 1974 to determine the economic practicality of the sterile-male approach as a control measure. Among the primary investigative areas under consideration were integrated control and population dynamics (Patterson et al. 1975). Since St. Croix is isolated by over 40 miles of water, the factor of immigration is considered minimal and a native fly residual, if present after sustained releases, would be attributable to other causes. The program consists essentially of mass rearing stable flies on the island, sterilizing 24 to 48-hr-old adults at 2 kR in a i"Co irradiator and releasing them at the many sites of fly infestation. Sterility and fly population densities are subsequently assessed by egg hatch evaluations, by the number of flies captured in animal traps, and by a count of the number of flies resting on a random sample of dairy cattle. Two gamma irradiators are available on St. Croix. They are for all purposes comparable except that one (Gammacell 220*) has a dose rate of 5088 r/min while the dose rate of the other (Radocell*) is 560 r/min. Be