[en] A programme to develop genetic sexing mechanisms in the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann), was initiated at the IAEA Laboratories, Seibersdorf, in 1983. Because of the potential benefits arising from the elimination of females early in the developmental cycle, combined with the anticipated relative ease of inducing temperature sensitive lethal (tsl) factors, it was decided to attempt to induce and isolate tsl factors active in the egg or early larval stages. Initially, five recombination suppressor (RS) strains were isolated. The degree of recombination suppression ranged from 77.6% to 99.1%. The viability of each of the five RS strains was assessed and RS 30/55 was selected as the most suitable strain. Ethyl methanesulphonate (EMS) was used to induce the tsl factors, by feeding two-day old adult males with a suspension of EMS in a 10% solution of sugar in the drinking water supply. Temperature tolerance tests indicated a discriminating temperature of 32 deg. C when isolating tsl factors active in the egg stage and 35 deg. C when isolating such factors in the early larval stage. A total of 39 and 22 tsl factors have been isolated in the two stages, respectively. However, none has yet proved stable. Induction of tsl factors with a reduced dose of EMS is now being attempted. An alternative genetic sexing programme was initiated in 1985, based on the use of pupal colour dimorphisms. Previously, a genetic sexing strain, T:Y(wp⁺)101, based on a white female/brown male puparial colour dimorphism, had twice been assessed for stability under mass rearing conditions. In both cases the sexual colour dimorphism disintegrated immediately. Another similarly dimorphic strain, T:Y(wp⁺)30C, was developed. This strain remained stable for seven generations of mass rearing, after which it started to disintegrate. Disintegration of this strain was probably caused by accidental contamination by wild type medflies. 34 refs, 1 fig., 1 tab

[en] The development of stable genetic sexing strains in the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann), is hampered by the presence of low levels of male recombination. Such recombination may be reduced by minimizing the distance between the translocation breakpoint and the translocated 'sexing' allele. Cytogenetic analysis of mitotic/meiotic and polytene chromosomes could provide information on the selection of such potentially stable genetic sexing strains. Translocation breakpoints in two genetic sexing strains in the medfly, based on a white female/brown male pupal colour dimorphism, have been determined. Preliminary results are described and the advantages and limitations of polytene chromosome analysis for the isolation of stable genetic sexing strains of the medfly are discussed. (author). 31 refs

[en] The induction and isolation of a multiple translocation strain in the Mediterranean fruit fly is described. Cytological analysis of this strain, T30C, showed the presence of a reciprocal autosomal translocation. In addition, a Y-autosome translocation, not involved in the reciprocal A-A translocation, was observed in meiotic chromosome preparations on a single occasion. Male viability of T30C was reduced both in the homozygous and in the heterozygous configurations when measured as egg hatch and as adult emergence, whereas a significant reduction in female viability was observed only in the egg hatch of the homozygous configuration, thus indicating the possible presence of chromosomal aberrations in male flies that are not present in female flies. T30C was back-crossed with the homozygous wp mutant, resulting in the genetic sexing strain T:Y(wp⁺)30C, in which males emerge consistently from brown puparia and females from white. Laboratory scale rearing for 24 generations provided no indication of instability in this strain. Mass rearing for ten generations resulted in the presence of 2.3% fertile females among the brown pupae, the first such females being observed in generation 4. A very low level of males emerging from white puparia was observed in almost every generation from the parental generation onwards. However, this level did not appear to increase. The possible cause of the observed low level of instability in T:Y(wp⁺)30C when mass reared is discussed, and it is concluded that this was caused by the accidental introduction of foreign gene pools. The overall viability of the mass reared T:Y(wp⁺)30C did not differ significantly from that of the standard mass reared 'Sohag' strain. The stability and viability of T:Y(wp⁺)30C thus renders this strain suitable for inclusion in sterile insect technique (SIT) programmes dependent upon the release of only the male sex. (author). 27 refs

[en] Published in summary form only

[en] The MP (male producing) factor, which shows temperature sensitive meiotic drive favoring the Y chromosome, proved to be highly variable in spermatozoal deficiency in different cysts within a single testis. However, the overall loss of sperm corresponded almost precisely with the loss of females. The minimum proportion of females consistently obtained in inbred lines was about 30-35%. On the basis of parallel studies with the mosquito Aedes aegypti, variability between cysts is open to interpretation in terms of different rates of senescence. The T:Y(wp⁺)30C genetic sexing strain, which is designed to generate males with brown (wild type) puparia and females with white puparia, was contaminated artificially in a series of population experiments to investigate the pattern of breakdown. Wild type contamination with either sex caused an increase of brown pupae. The sex ratio became progressively distorted in favour of females after contamination with females, mated or unmated, but not after male contamination. The experiments revealed evidence of a low frequency of natural recombination between wp⁺ and the translocation breakpoint on the Y chromosome, shown by the appearance of wp males. The frequency of male recombination (r) and the selection coefficient (s) against wp/wp were measured over 11 generations. The best fit to the observed data was obtained with r = (0.14 ± 0.04)% and s=(26.0 ± 2.7)%. Using these estimates to predict the frequency of wp⁺ females and wp males for up to 100 generations, it was concluded that white males would never exceed 0.5% whereas the frequency of brown females was expected to exceed 33% after 25 generations. Published data on the mass reared strain, maintained with a population size of 240,000 adult flies, were subjected to the same analysis. A higher value of s between (38.0 ± 3.2)% and (52.0 ± 0.3)% was obtained under these conditions. Electrophoretic studies on esterases revealed a significantly higher activity in a recently colonized strain from Morocco than in two laboratory strains (H1 and TY4). No change in activity was observed in this strain during the first three generations of laboratory culture. (author)