Radiation induced semi-sterility for genetic control purposes in the onion flyHylemya antiqua (Meigen) : I. isolation of semi-sterile stocks and their cytogenetical properties.

In the preliminary stages of a study into the use of translocations for genetic control of the onion flyHylemya antiqua (Meigen), irradiations were carried out in order to obtain chromosomal rearrangements. Several irradiation experiments, with X-rays or fast neutrons, were carried out on pupae and adults of both sexes at substerilizing doses below 3.0 krad, to establish a favourable way of induction.Because no visible markers are available for the genetic screening of induced rearrangements, and the reciprocal translocations or inversions in demand express themselves in the heterozygous condition by reduced fertility, a total of 234 F1 individuals of both sexes were checked for reduced fertility. 50 F1 individuals were suspected of carrying a translocation or inversion when they produced an egg hatch of between 30 and 60% (semi-sterility).This category was passed for cytogenetic analysis. In the progeny of 25 suspect F1 individuals, 9 different rearrangements were established, of which 7 were translocations. This means a yield of 4% for all the tested F1 After a discussion of the normal karyotype, some of the observed rearrangements are described.Irradiation of males with 1.0 krad of X-rays is advised for the production of semi-sterile stocks carrying translocations. Fast neutrons were not found to be better than X-rays. At doses higher than 1.0 krad complex rearrangements and/or fragments were observed.A translocation homozygote could be isolated in the case of an X-autosomal translocation, and this stock will be used for further genetic control purposes.