Laboratory Studies of Sterility and Competitiveness of Boll Weevils Irradiated in an Atmosphere of Nitrogen, Carbon Dioxide, or Air

Almost all male Anthonomus grandis grandis Boheman treated with 7 krad of gamma irradiation in air were dead within 14 days but over half of the males irradiated in an atmosphere of nitrogen lived for at least 21 days. Males were still 98–100% sterile when allowed to mate 3 and 7 days after treatment with 7 krad in nitrogen; however, by the 10th day, sterility had dropped to ca. 85%. Dissections on the 21st day posttreatment revealed that many males had enlarged testes with sperm bundles, indicating that they had recovered fertility. A dosage of 10 krad in nitrogen was required to maintain a level of at least 99% sterility; at this dosage level, survival, sterility in both sexes, and male mating capability were the same as for 8 krad in air. In laboratory tests, sexual competitiveness of males exposed to 10 krad in nitrogen (0.85) was significantly higher than that of males exposed to 8 krad in air (0.51). These competitiveness values from the laboratory studies were much higher than the published figures for weevil competitiveness in the field (0.17–0.36). This lack of agreement indicates that not all of the significant factors associated with male competitiveness are measured by the usual laboratory tests.