Viability and behaviour of translocations that suppress female recombination in the Mediterranean fruit fly,Ceratitis capitata (Wied.)

Summary The viability of a series of recombination suppressor (RS) strains in Ceratitis capitata, all previously found to contain a reciprocal autosomal translocation, was assessed for egg hatchability and adult emergence in both the homozygous and heterozygous state. Except in T 30C, which contains a Y-autosome translocation in addition to the A-A translocation, egg hatch was significantly reduced in all heterozygous translocation strains, and ranged from 42.4% to 58.5% in seeded eggs compared to a control value of 82.8%. Adult emergence from hatched eggs was affected to a lesser extent, but with a range of 59.5% to 84.2%, compared to the control value of 83.1%, remained significantly reduced in 4 of the 6 translocation strains, as well as in the male line of T 30C. In the homozygous configuration all strains, except T 19 and T 109, showed a significant reduction in egg hatchability, whereas adult emergence was not adversely affected. A significant reduction in the egg hatchability of the translocation heterozygotes compared to that of the homozygotes was observed in 5 of the 7 strains, the observed reduction in T 55/109 being non-significant while that of T 30C was significantly increased. The behaviour of translocations as recombination suppressors and their suitability for inclusion in breeding schemes for the isolation of induced recessive mutations is discussed.This work forms part of a Joint FAO/IAEA research programme on the development of genetic sexing mechanisms for the Mediterranean fruit fly, Ceratitis capitata (Wied.)     

Microsatellite analysis reveals remating by wild Mediterranean fruit fly females,Ceratitis capitata

Accurate estimates of remating in wild female insects are required for an understanding of the causes of variation in remating between individuals, populations and species. Such estimates are also of profound importance for major economic fruit pests such as the Mediterranean fruit fly (Ceratitis capitata). A major method for the suppression of this pest is the sterile insect technique (SIT), which relies on matings between mass-reared, sterilized males and wild females. Remating by wild females will thus impact negatively on the success of SIT. We used microsatellite markers to determine the level of remating in wild (field-collected) Mediterranean fruit fly females from the Greek Island of Chios. We compared the four locus microsatellite genotypes of these females and their offspring. Our data showed 7.1% of wild females remated. Skewed paternity among progeny arrays provided further evidence for double matings. Our lowest estimate of remating was 3.8% and the highest was 21%.     

Molecular sexing in the Mediterranean fruit fly, Ceratitis capitata

Molecular methods have been devised for sexing Mediterranean fruit fly (medfly) individuals using minimal amounts of material from any stage of the life cycle. Molecular sexing methods are particularly valuable when material is obtained from pre-adult stages and sex identification based on morphological characters is not possible. These methods may also be useful for adult stage material in situations where only limited amounts or poorly preserved specimens are available. The sexing methods described here use the polymerase chain reaction (PCR) to amplify sequences known to originate from the sex chromosomes of this species. One method co-amplifies homologous regions of the ITS1 ribosomal DNA from both the X and Y chromosomes. Males and females are distinguished based on the restriction fragment pattern produced after digestion of the PCR products with the restriction enzyme ApoI. A second method identifies males based on the positive amplification of a repetitive DNA sequence originating from the Y chromosome. Both methods are shown to be capable of establishing the sex identity of individuals using only minimal amounts of material from any stage of the life cycle.     

地中海实蝇地理种群遗传分化研究

以mtDNA的CO Ⅰ基因的部分序列作为分子标记,研究了来自安哥拉、黎巴嫩、刚果共和国、尼日利亚、贝宁、多哥、加纳、科特迪瓦、南非、埃及、法国、约旦、秘鲁、智利、美国佛罗里达和美国夏威夷等16个国家和地区共75个个体的地中海实蝇Ceratitis capitaza地理种群序列特征和单倍型特征,并分析了各种群间的遗传分化水平和进化关系,结果表明,在供试的样品中发现单倍型的数目是29,其中有5种为共享倍型.地中海实蝇各地理种群的遗传多态性水平差异较大,总体遗传距离D等于0.007.非洲南撒哈拉区(安哥拉、刚果、尼日利亚、贝宁、多哥、加纳、科特迪瓦)的种群的单倍型数、单倍型百分比和群内遗传距离等遗传多态性参数值都高于其它供试地区,多样性明显较其他地区丰富.     

Host-specific demographic studies of the Mediterranean fruit fly Ceratitis capitata

Abstract. 1. This study was conducted in Greece using a wild strain of medflies ( Ceratitis capitata [Weidemann]) to assess age-specific vital rates in adults, and development and survival in pre-adults when reared on different host fruit. The results were used to construct life tables.
2. The demographic analyses suggested that there are basically four aspects of the medfly's life history which are of major importance: (i) multiple, highlyoverlapping generations; (ii) high net reproduction while young; (iii) high larval fitness in certain hosts; (iv) lack of diapause.
3. Reasons why these characteristics are felt to be important are briefly discussed.     

Improved stability of genetic sex-separation strains for the Mediterranean fruit fly, Ceratitis capitata.

In the existing genetic sexing strains for the medfly, Ceratitis capitata, male recombination leads to breakdown of the sexing mechanism under mass rearing conditions. The rate of breakdown depends on the recombination frequency and on the fitness of the recombinants. We have tested two different sexing genes, white pupa and a temperature sensitive lethal, in combination with the translocation T(Y;5)30C. Both sexing strains broke down, although at very different rates. In the case of the white pupa strain, 3.5% recombinants were observed after rearing the strain for 15 generations. The second strain, utilizing white pupa and the temperature sensitive lethal as selectable markers, already reached a comparable level after six generations and was broken down completely in the ninth generation. In these strains the frequency of recombination is high because the breakpoint of T(Y;5)30C and the sexing gene(s) are far apart. To remedy the situation, we have isolated four new translocations with breakpoints located closer to the sexing genes. Mass rearing was simulated for several generations with strains based on these translocations and no breakdown was observed under the conditions used.     

Field releases of two genetic sexing strains of the Mediterranean fruit fly (Ceratitis capitata Wied.) in two isolated oases of Tozeur governorate, Tunisia

The recent development of medfly genetic sexing strains (GSS) enables only male adults to be produced and released for area-wide control using the sterile insect technique (SIT). Before these strains can be incorporated into large operational field programmes, information is required on all aspects of field performance.
In a pilot project in Tunisia, medfly pupae from GSS SEIB-40 [based on a pupal colour mutation ( wp ) and VIENNA-43/44 [based on a temperature sensitive lethal mutation ( tsl ) were shipped from the FAO/IAEA Agriculture and Biotechnology laboratory (Seibersdorf, Austria) and the emerged sterile males released weekly from the ground in oases of the Tozeur Governorate from mid-February until October 1994. During that period, flies emerging from an average of 5000 pupae per hactare were released weekly throughout 105 hectares. Transportation problems were encountered which resulted in damage to the pupae. Nevertheless, the monitoring of the wild population through a trapping network using Jackson and McPhail traps showed that both strains performed equally well inducing a three- to five-fold decrease of the wild population compared with the control oasis (10 wild flies per Jackson trap per day in October in Ain-El-Karma, five in Tamerza and 30 in Bir Kastilia control oasis). Considering the economical and technical benefits inherent in the use of these new strains in the field and as a result of their good field performance, similar strains have been introduced into mass-rearing facilities in Guatemala (1994), Argentina (1995) and Madeira (1996).     

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

Using 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.

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Résumé Des expériences en cage en champ ont été réalisées en Italie avec des populations naturelles de Ceratitis capitata en utilisant une lignée dont le sexage 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.

     

Susceptibility of the Mediterranean fruit fly (Ceratitis capitata) and the Natal fruit fly (Ceratitis rosa) to entomopathogenic nematodes

The potential of entomopathogenic nematodes, Heterorhabditis bacteriophora, Heterorhabditis zealandica and Steinernema khoisanae, to infect pupariating larvae, pupae and adults of Ceratitis capitata and Ceratitis rosa was investigated in laboratory bioassays. Pupariating larvae and adult flies were susceptible to nematode infection, with no infection recorded for the pupae. Pupariating larvae of C. capitata were generally more susceptible to infection than those of C. rosa. Significantly more larvae of C. capitata were infected by H. bacteriophora. For C. rosa, highest infectivity of larvae was obtained with H. zealandica. In contrast, adults of both species were highly infected by S. khoisanae.     

Mass rearing of temperature sensitive genetic sexing strains in the Mediterranean fruit fly (Ceratitis capitata)

Genetic sexing strains (GSS) based on the temperature sensitive lethal(tsl) mutation are being used to produce sterile male medflies for large scale sterile insect technique (SIT) programmes for this pest. The use of male-only strains increases the overall efficiency of the technique. Currently more than 1.4 billion sterile male-only pupae are produced per week in different facilities around the world. Due to the mutations used to construct these strains, that is, translocations and selectable markers, they require different and more careful mass rearing procedures than do bisexual strains (BSS). The basic rearing technology has been developed and can be used to produce only males on a predictable basis to a level of 99.9% accuracy. If specific rearing procedures are followed, then tsl-based GSS has a rearing efficiency that is equal to that of a BSS and it is already know that males produced by the tsl-based GSS are of equal quality to males produced by BSS. Based on current rearing technology the cost of production of male pupae is about the same for both types of strain. This is due to the large colony that is required for the tsl-based GSS. This paper discusses the considerations that need to be taken into account during mass rearing of GSS and identifies the most efficient production processes that are currently available.     

Two-way selection for mating activity in the Mediterranean fruit fly, Ceratitis capitata

No significant variation in mating activity was observed among eight laboratory strains of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Two methods were used to select strains showing high and low mating activity: a single pair technique (SP) assessing time to mating and a mass technique (M) based on a mating index. Reciprocal pairings between fast and slow selected lines showed that the difference between the SP lines was female-determined whereas the difference between the M lines depended on the behaviour of both sexes. M selection, irrespective of its direction, affected two courtship parameters, vibration distance and vibration duration both of which tended to be shorter. M selection was also associated with a reduction in startle activity in females.

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Résumé Aucune variation significative n'a été observée dans les activités sexuelles de huit souches de laboratoire de la mouche méditerranéenne du fruit, Ceratitis capitata (Wiedemann) (Diptera Tephritidae).Deux méthodes ont été utilisées pour sélectionner des souches manifestant une activité sexuelle basse ou élevée: une technique utilisant un seul couple (SP), basée sur la durée de la période avant copulation, et une technique de masse (M), basée sur un index d'accouplement.Des appariements réciproques entre les lignées rapides et lentes ont montré que la différence entre les lignées SP était déterminée par les femelles, tandis que la différence entre les lignées M résultait du comportement des deux sexes. La sélection M, quelle que soit sa direction, affects deux paramètres, la distance entre partenaires lors de la vibration et la durée de la vibration qui tous deux tendent à se raccourcir. La sélection M est aussi associée à une réduction de la réaction des femelles à un brusque stimulus lumineux (Startle activity).

     

Interactions of mating,egg production and death rates in females of the Mediterranean fruit fly,Ceratitis capitata.

Costs of reproduction include costs of producing eggs and of mating itself. In the present study, we made an experimental investigation of costs of reproduction in the Mediterranean fruit fly (medfly, Ceratitis capitata). We demonstrated that virgins live longer than non-virgin females. However, in strong contrast to most findings within the Diptera, non-virginity had no detectable effect on egg production. Therefore the increased longevity of the virgin females cannot be attributed to an increase in egg production in non-virgin females, and instead indicates a cost of mating. A comparison of the life spans of normal females and those sterilized by low doses of X-irradiation, revealed an additional cost of egg production. There were no significant differences in remating levels between females that did and did not lay eggs, showing that the cost of producing eggs is independent of mating frequency. Medfly females therefore suffer a decrease in survival as a result of egg production and of mating, and these costs are independent of one another. To put our results into context, we reviewed the existing literature on the effects of mating on longevity, egg production and sexual receptivity for 64 species of Diptera, and examined the pattern of mating effects that emerged.     

Cytogenetic analysis of chromosome 5 from the Mediterranean fruit fly,Ceratitis capitata

A cytogenetic map of chromosome 5 from the Mediterranean fruit fly, Ceratitis capitata, was constructed. Six mutations were located by translocation, transposition or deletion mapping. This knowledge allowed alignment and orientation of the existing linkage map with the polytene chromosomes. In addition, mapping of mutations used as selectable markers in genetic sex-separation strains is an essential prerequisite for the improvement of genetic stability during mass-rearing.     

Ecological niches and potential geographical distributions of Mediterranean fruit fly (Ceratitis capitata) and Natal fruit fly (Ceratitis rosa)

Aim To predict and compare potential geographical distributions of the Mediterranean fruit fly (Ceratitis capitata) and Natal fruit fly (Ceratitis rosa). Location Africa, southern Europe, and worldwide. Methods Two correlative ecological niche modelling techniques, genetic algorithm for rule‐set prediction (GARP) and a technique based on principal components analysis (PCA), were used to predict distributions of the two fly species using distribution records and a set of environmental predictor variables. Results The two species appear to have broadly similar potential ranges in Africa and southern Europe, with much of sub‐Saharan Africa and Madagascar predicted as highly suitable. The drier regions of Africa (central and western regions of southern Africa and Sahelian zone) were identified as being less suitable for C. rosa than for C. capitata. Overall, the proportion of the region predicted to be highly suitable is larger for C. capitata than for C. rosa under both techniques, suggesting that C. capitata may be tolerant of a wider range of climatic conditions than C. rosa. Worldwide, tropical and subtropical regions are highlighted as highly suitable for both species. Differences in overlap of predictions from the two models for these species were observed. An evaluation using independent records from the adventive range for C. capitata and comparison with other predictions suggest that GARP models offer more accurate predictions than PCA models. Main conclusions This study suggests that these species have broadly similar potential distributions worldwide (based on climate), although the potential distribution appears to be broader for C. capitata than for C. rosa. Ceratitis capitata has become invasive throughout the world, whereas C. rosa has not, despite both species having broadly similar potential distributions. Further research into the biology of these species and their ability to overcome barriers is necessary to explain this difference, and to better understand invasion risk.     

The construction of the first balancer chromosome for the Mediterranean fruit fly, Ceratitis capitata

The construction of the first balancer chromosome, FiM1, for the medfly Ceratitis capitata is described. This chromosome has three overlapping pericentric inversions and is marked with dominant and recessive mutations. The inversion breakpoints of FiM1 suppress recombination throughout the length of the fifth chromosome, allowing lethal mutations to be recovered and maintained. This chromosome will provide a powerful tool for the manipulation of laboratory stocks, in particular, the recovery of new mutant and transgenic strains. We demonstrate the use of FiM1 for the recovery and maintenance of chromosomes carrying lethal mutations.     

Sexual competitiveness of a transgenic sexing strain of the Mediterranean fruit fly, Ceratitis capitata

The sterile insect technique (SIT), when used for the control of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), generally relies on the release of sterile flies of only the male sex. Male selection is achieved through the use of a genetic sexing strain (GSS) in which females are killed by heat treatment in the generation prior to release. Transgenic sexing strains (TSS) have been developed that perform the same function of female-lethality, this time by withholding tetracycline (or related compounds) from the larval diet. The use of TSS may allow for certain problems associated with conventional GSS, such as strain instability and reduced productivity in mass-rearing, to be avoided. The performance, and principally the sexual competitiveness, of released male flies is important for the success of an SIT control programme. This study describes field cage experiments in which the competitiveness of males from a TSS (OX3376B) was compared with that of a conventional GSS (VIENNA-8) and two wild-type strains (TOLIMAN and ARG). When competing for female mates with wild-type males, OX3376B male performance was acceptable. When OX3376B males competed directly for mates with VIENNA-8 males, VIENNA-8 slightly outperformed the TSS males. Parallel tests, in which wild-type males competed with either OX3376B or VIENNA-8 males, showed that males from both sexing strains were highly competitive with wild-type males. These results suggest that OX3376B in particular, and TSS in general, show sufficiently good mating competitiveness to merit further research into their suitability for eventual use in SIT programmes.