Radiation sterilization of Glossina tachinoides Westw. pupae. I. The effect of dose fractionation and nitrogen during irradiation in the mid-pupal phase

Abstract

A study was carried out to analyze the effect of nitrogen during radiation and dose fractionation on Glossina tachinoides pupae during the mid-pupal phase (day 15 - 20 following larviposition (PL)). The radiation protective effect of nitrogen during treatments of 10 - 80 Gy of 15 - 20-day-old pupae was demonstrated by an increased total eclosion rate (for 15-day-old pupae), higher residual male fertility levels (34.6 and 44.6 % for 15 and 20-day-old pupae treated in nitrogen respectively versus 19.1 and 5.9 % for treatments in air) and distinctive longer life spans. The proportion of reproductive abnormalities observed in their female mates increased with increased radiation dose, when treated at younger pupal stages and following treatment in air. After treatment of 15day-old pupae with 10 Gy in nitrogen, female fertility was 0.068 pupae per mature female day as compared to 0.035 pupae/m.f.d. in air. No such increase was observed when treated as 20-day-old pupae. A dose of 60 -SO Gy in nitrogen administered to 20-day-old female pupae was required to obtain 95 % sterility. Splitting the radiation dose in nitrogen atmosphere in 2 fractions 1,2 and 5 days apart (first dose of 10 Gy given on day 15 PL) did not influence the total eclosion rate, mating response or insemination capacity of the male flies. Sterility of males treated in fractions separated by 1 and 2 days was similar to the level in those given a continuous dose on day 15 PL but the level of induced lethal mutations decreased with fractions separated by 5 days. Survival of the males treated in fractionated doses was similar as compared with males treated with one continuous dose on day 20 PL but better when compared with males treated with one continuous dose on day 15 PL. Female fecundity was reduced by splitting the radiation dose in fractions 1 and 2 days apart. Complete sterility was induced in female pupae when fractions were separated by 5 days, irrespective of the radiation dose used in this study. Irradiation of G. tachinoides pupae in the mid-pupal phase in nitrogen with doses split in 2 fractions separated by 1 or 2 days (total dose of 40 Gy) or 5 days (total dose of 60 - 80 Gy) resulted in high quality (average longevity > 20 days), sterile (residual fertility < 5 %) male flies.