Pheromone Production and Sterility in Boll Weevils: Effect of Acute and Fractionated Gamma Irradiation

Each of 3 methods of irradiating male Anthonomus grandis Boheman resulted in a unique pattern of pheromone production over a 12-day period of observation. Peak pheromone production occurred 4–6 days after treatment in males given a single large dose of gamma irradiaton (acute irradiation) at the age of 4 days and in males given small increments of irradiation (fractionated irradiation) during the late pupal and early adult stages. Both groups produced much less pheromone during the next 3 days. The acute irradiated weevils, destined to die soon, produced no pheromone after the 9th day, whereas the fractionally irradiated males began to show a partial recovery. Males fractionally irradiated entirely during the adult stage produced a moderate but constant amount of pheromone during the entire 12-day period. Measurements of attractiveness of treated males placed in field traps produced results that were in general agreement with the laboratory data. Male sterility for all 3 treatments was ca. 99%, and from 66–82% of the males were able to transfer sperm 7 days after treatment. Females irradiated during the pupal and adult stages were completely sterile, producing no eggs. The 2 groups of females irradiated as adults produced some egiS and it was necessary to incorporate a dip treatment consisting of 0.02% diflubenzuron (Dimilin®; N -[[(4-chlorophenyl) animo] carboynl]-2,6-difluorobenzamide) in acetone to suppress viability.