Sexual competitiveness of irradiated male Glossina palpalis gambiensis reared in vitro for more than 20 years

Full text: The effects of irradiation and the number of successive matings on sexual potency, sperm transfer ability as well as the survival of sterile males of Glossina palpalis gambiensis, maintained on an in vitro system since 1984 at CIRDES, are evaluated. Three experimental groups and one control group comprised each of 90 males aged 6 days, are successively, six times, introduced into mating cages with 2-3 days females, at 48 hours interval and at a ratio of 1/1. The 3 experimental groups of males were irradiated from a gamma source, Caesium137, at doses of 102, 112 and 122 Gy. After 45 days, the survival of the males was evaluated and the females dissected to determine insemination rate and the degree of spermathecal fill. No significant difference was observed between the rates of survival of the irradiated and unirradiated males. The average rates were 76% in about 2 weeks, and 20% after 45 days. The irradiated and unirradiated males showed a good mating activity and sperm transfer capacity. However, a significant difference was observed at the 5th mating in the insemination rate of the females which decreased from 84.75% to 63.93%. The degrees of sterility induced in the females during the six successive matings varied from 89.83 to 95.22%. In a second phase, tests of competitiveness were carried out between these males irradiated with a dose of 112 Gy and unirradiated wild males captured from the field in Mali. The test release of flies was conducted in a field cage in the presence of females of the wild stock. The entire results indicated that sterilisation with the gamma rays and the six successive matings did not have any significant effect on the survival, the behaviour or the sexual performance of the reared sterile males. This work is part of the quality control assessment of reared sterile males produced in CIRDES for experimental releases in the peri-urban zone of Bamako, Mali. (author)