Genetic Sexing Strain Research Articles

Stability of Two Mass-Reared Genetic Sexing Strains of Ceratitis capitata (Diptera: Tephritidae) Based on Pupal Color Dimorphisms

Two genetic sexing strains of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) were mass-reared. Both strains contain a Y-autosome translocation which links the wild-type brown allele of the white pupae (wp) gene to the male-determining Y chromosome. Continuous inbreeding of each strain results in the production of brown male and white female puparia, thus enabling the automated separation of the sexes before release of sterilized males in sterile insect technique pest management control or eradication programs against this pest. Past experience has shown such strains to be prone to breakdown through a variety of mechanisms. The present experiments were designed to assess the stability of both strains under mass-rearing conditions. Aberrant brown female pupae appeared in the T:Y(wp+)101 strain in the first generation of mass rearing. By the fifth generation, the reproducing component constituted 24.4% of the brown pupae. The corresponding level of aberrant phenotypes in the brown pupae of the T:Y(wp+)30C strain was 2.3% by generation 10. The first reproducing aberrant females appeared in generation 4 of this strain. The frequency of reproducing aberrant white male pupae in T:Y(wp+)101 also increased with successive generations, reaching 12.4% in generation 5. No increase in aberrant white males was observed in T:Y(wp+)30C. The results indicated that the breakdown of the T:Y(wp+)lOl strain was caused by a low degree of male recombination combined with a high genetic load carried by the mutant wp allele. Whether or not the rate of breakdown observed in this strain was accelerated by an accidental introduction of wild-type genotypes could not be conclusively determined. The slight breakdown in T:Y(wp+)30C was attributed solely to an introduction of wild-type material, and no indication of male recombination could be found. The overall viability of the latter strain was not significantly different from that of the standard, mass-reared “Sohag” strain. It is concluded that T:Y(wp+)30C is acceptable for mass rearing and that it shows excellent potential for utilization in sterile insect technique programs relying and depending upon the release of genetically sexed sterile males.

Field cage studies with a genetic sexing strain in the Mediterranean fruit fly, Ceratitis capitata

AbstractUsing a genetic sexing line based on pupal colour dimorphism in Ceratitis capitata Wied., field cage experiments were carried out with a wild population in Italy. The experiments were designed to monitor the competitiveness of males of this line in comparison with wild males and to assess the effect of removal of females prior to release on the proportion of wild females mated by the released males.The results showed that the genetic sexing strain competed well with the wild population but there was a large degree of intra‐strain mating. Removal of females prior to release radically changed the mating pattern from intra to inter‐strain mating. This change greatly increases the efficiency of the sterile insect method of control.It was concluded that as well as the obvious economic advantages of genetic sexing, significant biological advantages would also be associated with the integration of such a strain in a sterile insect control programme.RésuméExpériences en cage au champ avec des lignées génétiquement sexables de Ceratitis capitataDes expériences en cage en champ ont été réalisées en Italie avec des populations naturelles de Ceratitis capitata en utilisant une lignée dont le sex‐age était basé sur le dimorphisme de la couleur des pupes. Les expériences ont été conçues pour contrôler la compétitivité des mâles de cette lignée face aux mâles sauvages, et d'évaluer l'effet du retrait des femelles avant le lâcher sur le pourcentage de femelles sauvages accouplées avec des mâles lâchés.Les expériences montrent que la compétition ne défavorise pas la lignée génétiquement sexable mais révèlent une fréquence élevée d'accouplement intralignée.Le retrait des femelles avant le lâcher modifie radicalement l'orientation des accouplements d'intra vers interlignées. Ce changement accroît fortement l'efficacité de la technique d'utilisation des mâles stériles dans la lutte biologique. On en a conclu que non seulement des intérêts économiques évidents mais aussi des avantages biologiques significatifs seraient retirés de l'intégration de telles lignées sexables génétiquement dans les programmes de lutte avec des mâles stériles.

Use of a Commercial Color Sorter to Separate Sexes of Stable Fly (Diptera: Muscidae) Pupae from a Genetic Sexing Strain

A genetic sexing strain of stable flies, Stomoxys calcitrans (L.), with females having black pupal color and males having brown pupal color was selected in a color sorter with ca. 99% accuracy. A single-channel machine could sort 1. 7 million pupae in 24 h. Use of this color sorter and this genetic sexing strain show promise for use in integrated control programs using sterile male releases.

Effect of Genetic Recombination in Males of the Mediterranean Fruit Fly (Diptera: Tephritidae) on the Integrity of “Genetic Sexing” Strains Produced for Sterile-insect Releases

Construction of “genetic sexing” strains of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), for use in sterile-insect technique projects, depends on a close linkage of the sexing trait with the male's sex-determining chromosome. Genetic recombination in males was observed for two linkage groups and its possible effects on the linkage of the sexing trait to the male's sex chromosome was studied. A model was developed to evaluate the consequences of recombination in males on the integrity of genetic sexing strains. Actual data suggest that other mechanisms operate in such strains, causing the deterioration and reshuffling of the sexing trait.

Mating Competitiveness of Irradiated Male Stable Flies, Stomoxys Calcitrans (Diptera: Muscidae), from a Genetic Sexing Strain

A genetic sexing strain (GSS) of stable flies consisting of dieldrin-resistant males and dieldrin-susceptible females was used in this study. The GSS males were subjected to dieldrin as larvae and irradiated as adults for competitiveness tests against males that were not exposed to dieldrin or radiation. The irradiated GSS males were about equally competitive with untreated males in these tests. Tests with a mutant marker strain showed that females mate only once.