[en] Although the medfly is a key pest in many areas of the world, there are important fruit growing areas where other fruit flies are key pests. It was concluded that it would be of value for any future CRP on genetic sexing to include these species. For the development of genetic sexing systems in these species much can be gained from the experiences with the medfly. However, at present, a similar procedure will have to be followed which will entail the construction of genetic maps, the development of cytological techniques and the induction of male linked translocation. In future, the availability of molecular methods could enable sexing systems to be transferred between species. The proceedings contain 11 papers, which range from an initial molecular analysis of the genome of the fly to a field experiment to assess the impact of an all-male release

[en] The present status in genetic sexing for the Mediterranean fruit fly is discussed. This includes the selection of the appropriate sexing gene (which determines the feasibility and practical applicability of the sexing system) as well as the selection of the appropriate Y-autosome translocation (which determines the stability of the sexing system). A temperature sensitive lethal mutation is used to eliminate females during the egg stage. This mutation in combination with new Y-autosome translocations allowed the construction of a genetic sexing strain, named VIENNA-42, that is stable enough for large scale mass rearing. Also described are the analysis of this strain under field cage and field conditions and, in preparation for large scale tests in Guatemala, the outcrossing of VIENNA-42 with genetic material from the target area. (author)

[en] The author makes suggestions on the direction of research for genetic sexing over the next several years and prepared the paper as a guide for discussion. The literature of genetic and cytogenetic studies on insects as a whole is the basis for most of the approaches that the genetic control community has used, but only a tiny fraction of the literature is directed at genetic sexing and most of that is limited to, small scale laboratory studies. The effort to use genetic sexing strains on the scale of mass rearing of medflies is unprecedented, and it is not surprising that a few problems have been encountered during implementation. Consideration of this fact leads to the conclusion that it is necessary to 'think big' and target the research. (author)

[en] Cloned DNA sequences were hybridized to salivary gland polytene chromosomes of the medfly, Ceratitis capitata, establishing molecular markers for 55 sites on all (ten) autosome arms. Fourteen of the markers correspond to characterized medfly transcription units, while the function of the remaining clones is unknown. Five additional markers were identified as repetitive elements that hybridized to a large number of autosomal sites and also to the granular network that represents the X chromosome. Some of the clones were also hybridized to polytene chromosomes from the orbital bristle cells of C. capitata to align the two types of polytene chromosomes, which differ significantly in their banding pattern. (author)

[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)

[en] A review is presented of results obtained in a search for genetic markers, translocations and selectable genes obtained at the Instituto de Genetica, Castelar, Argentina, with special reference to chromosome 2 linked mutations and genes useful for developing self-sexing strains in Ceratitis capitata. (author)

[en] The authors describe their first efforts to construct 'balancer' chromosomes for the Mediterranean fruit fly, Ceratitis capitata. The experiments were focused on chromosome 5, which is genetically the best characterized medfly chromosome. Following the synthesis of a multiple marker strain for chromosome 5, bearing the Cy mutation as a selectable marker, attempts were made to induce chromosome rearrangements by gamma irradiation and select those chromosomes showing crossing-over suppression. During this process the cytological mapping of the Cy mutation was achieved. (author)

[en] Large scale field studies of the Mediterranean fruit fly, Ceratitis capitata, were carried out in Hawaii using a genetic sexing strain based on pupal colour. In a ground release population suppression study, an all-male release was compared with a bisexual release; also included was a release of predominantly females. Following release, egg hatch measurements in the field indicated that the release of males was about four times more effective than the release of males and females. The release of females only, as expected, failed to show any effect on egg fertility. During the latter part of the releases it appeared that the wild medfly population was developing some form of behavioural resistance to the released sterile males. (author)

[en] Altogether 27 morphological mutations on the five autosomes of the Mediterranean fruit fly, Ceratitis capitata (Wied.), have been isolated and studied in the author's laboratory during 22 years of research on the genetics of this species. Of the 27 loci, 18 were located on chromosomes 4 and 5. No mutant loci were identified on the sex chromosome in the laboratory. Linkage relations, map distances and linear arrangements on the respective chromosomes were established for most of the 27 mutant traits. The wp and dp traits were utilized in the construction of genetic sexing lines in laboratories involved in studies of the sterile insect technique. The occurrence and consequences of male recombination are discussed. (author)

[en] Multilocus enzyme electrophoresis (MLEE) and random amplified polymorphic DNA were used to detect genetic markers in Ceratitis capitata. The authors employed both types of markers (1) to study the genome organization of the medfly, (2) to determine the level of intraspecific genetic diversity, and (3) to understand the evolution of the geographical populations. Sterility and high mutation rates in interstrain crosses were observed in C. capitata, reminiscent of hybrid dysgenesis in Drosophila, and may represent the activation of mobile elements, useful for medfly transformation. The biochemical, genetic and molecular characterization of the enzyme alcohol dehydrogenase clarified the peculiarity of this selectable system, compared with that of Drosophila, and revealed a surprisingly high sequence variability in medfly populations. The phylogenetic relationships between C. capitata and other Tephritidae species of economic importance were analysed by the MLEE approach. (author)