Genetic sexing in the mediterranean fruit fly,Ceratitis capitata,using the alcohol dehydrogenase locus

Summary Using the alcohol dehydrogenase (ADH) locus a genetic sexing system is being developed in the Mediterranean fruit fly Ceratitis capitata based on the sensitivity of ADH null mutations to environmental ethanol. A series of null mutants have been induced at this locus, however, none proved viable as homozygotes. One of these null mutants was translocated to the male determining chromosome and this line can be used for genetic sexing. When larvae from this line were reared on larval medium containing various concentrations of allyl alcohol, 97% of the emerging adults were males; in the absence of the allyl alcohol the sex ratio in the line is distorted in favour of the females. It is proposed that the higher ADH activity of the females (homozygous positive) in comparison with the males (heterozygous null) is responsible for their lower survival in larval medium containing allyl alcohol. ADH converts the allyl alcohol to the lethal ketone. The possible use of this line to sex large populations of medflies for use in sterile insect release programmes is discussed.     

Assessment of quality control parameters during mass rearing of a pupal colour genetic sexing strain of the Mediterranean fruit fly

Quality control charts were employed to monitor the quality of several parameters during mass rearing of the T : Y(wp ⁺)30C strain of Ceratitis capitata (Wiedemann), in which male and female flies emerge from brown and white puparia, respectively. Egg hatch and pupal recovery in this genetic sexing strain were below that reported for a wild-type Sohag strain, whereas pupal size, adult emergence and flight ability were higher. The overall recovery from eggs to adult flies capable of flight was similar in the two strains but egg production in T:Y(wp ⁺)30C was reduced to about 56% of that of Sohag. The quality control charts showed an acceptable level of variation within sets of data but the level between data sets was occasionally out of control. This indicated the presence of uncontrolled conditions during the rearing process, possibly arising from variations in the quality of the larval diet. It is concluded that the quality of T : Y(wp ⁺)30C renders this strain suitable for mass rearing in sterile insect technique (SIT) programmes requiring the elimination of the female flies prior to the release of sterilized males. The next step should involve further quality assessments both under field cage and under field release conditions. The importance of optimal and standardized dietary conditions is stressed in relation to the quality of mass reared medflies.

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Résumé Des normes de qualité ont été utilisées pour relever la valuer de plusieurs paramètres lors de l'élevage industriel de la souche T : Y(wp ⁺)30C de C. capitata Wied. dont les mâles et les femelles émergent respectivement de pupes brunes et blanches. Les taux d'éclosion et d'obtention de pupes sont plus faibles avec cette souche qu'avec la souche souvage Sohag; par contre, la taille des pupes, le taux d'émergence des adultes et l'aptitude au vol étaient plus élevés. La fréquence totale des adultes capables de voler par rapport au nombre initial d'ufs a été de 0,297 contre environ 0,311 pour Sohag. Cependant, la production d'ufs a été réduite à environ 56% de celle de Sohag. Les tableaux de contrôle de la qualité ont révélé un niveau de variation acceptable à l'interieur rieur des lots de données, mais la variabilité entre les lots excédait les normes admissibles. Ceci implique des paramètres incontrôlés pendant l'élevage de masse, probablement liés à des variations de la qualité de l'aliment. On peut en conclure que la qualité de la souche T : Y(wp ⁺)30C la rend utilisable pour un élevage de masse dans des programmes d'utilisation d'insectes stériles (SIT) exigeant l'élimination des femelles avant le lâcher de mâles stériles. La prochaine étape impliquera de nouvelles épreuves de qualité dans des cages en champ et dans les conditions de libération dans la nature. L'importance des conditions optimales d'une alimentation standardisée est soulignée par la qualité des mouches obtenues en élevage de masse.

     

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.)     

Isolation and cytogenetic analyses of genetic sexing strains for the medfly,Ceratitis capitata

Over the last 10 years, several genetic sexing strains have been isolated for the Mediterranean fruit fly, Ceratitis capitata, with the aim of improving the Sterile Insect Technique. However, a major problem with the currently used genetic sexing system, which is based on translocations, is their potential genetic instability. Therefore, careful monitoring and chromosome analyses are necessary when new genetic sexing strains are developed. Instability of a genetic sexing strain can be the consequence of recombination or the survival of aneuploid individuals occurring as a consequence of adjacent-1 segregation in the meiosis of males with Y-autosome translocations. Recently, genetic sexing strains have been isolated that show only low levels of recombination. However, many aneuploid flies are produced by these strains. Therefore, we have made an attempt to isolate new genetic sexing strains that show a low percentage of recombination and no survival of aneuploid individuals. We report their genetic behaviour and the polytene chromosome structure of these new strains.     

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.     

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.     

Cytogenetic analysis of three genetic sexing strains of Ceratitits capitata

Summary Polytene chromosomes of three genetic sexing strains of Ceratitis capitata were analyzed. The genetic sexing mechanism is based on a pupal color dimorphism (white-brown) and is the result of a reciprocal translocation between the Y chromosome and the autosome bearing the w locus (white pupal case). The analyzed polytene chromosomes were derived from two different pupal tissues, the orbital bristle and fat body cells. The Y chromosome is visible in both tissues, while the autosomes present a different banding pattern. Based on these features, the autosome breakpoints in the three Y; autosome translocations were mapped, and the homology of the translocated autosome in both tissues was established. In addition, the location of the break-points was compared to the stability of these three strains.     

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).

     

Performance of controlled-release formulations of trimedlure to attract the Mediterranean fruit fly, Ceratitis capitata

Mediterranean fruit flies (Ceratitis capitata Wied.) are detected by traps baited with the attractant, trimedlure (TML), deposited on the standard cotton dental roll dispenser. Since this dispenser is effective for only 2–4 weeks, controlled-release dispensers may extend the field life of TML-baited traps. A polymeric plug containing 70% by weight TML was highly effective for 8–12 weeks. Other formulations were less effective in the tests with released flies. A release rate of ca. 17 mg of standard TML/day or higher gave insect captures which were generally lower but statistically equivalent to those with the reference dispenser which released 61–63 mg/day. Normalized insect catches increased approximately as the square root of the release rate; the curvilinear regression equation suggested that TML release rates of ca. 52 and 15 mg/day give insect captures equal to ca. 100% and 50%, respectively, of the reference catches. The most attractive TML isomer (TML-C) was a highly effective attractant at a release rate of ca. 4 mg/day.

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Résumé C. capitata était attiré par des pièges alimentés avec de la trimedlure (TML), attractif déposé sur un distributeur commercial de coton dentaire en rouleau. Puisque ce distributeur ne fonctionne que 2 à 4 semaines, des distributeurs à libération contrôlée peuvent augmenter le temps de fonctionnement de pièges fournis en TML. Un bouchon en polymère contenant en poids 70% de TML a été très efficace pendant 8 à 12 semaines. D'autres formules ont été moins efficaces avec des mouches lâchées. Un taux de libération, de 17 mg ou plus de TML moyen par jour, capture moins, mais sans différence statistique significative, qu'un distributeur témoin qui libérait 61 à 63 mg/j. Les captures d'insectes ont augmenté à peu près comme le carré du taux de libération; l'équation de régression curviligne a conduit à penser que la libération de TML à des taux de 52 et 15 mg/j, provoque des captures égales à 100% et 50% des captures de référence. L'isomère le plus attractif (TML-C) a été un attractif très efficace au taux de libération de 4 mg/j.

     

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.     

Mitochondrial DNA restriction map for the mediterranean fruit fly,Ceratitis capitata

Molecular genetic research on the Mediterranean fruit fly,Ceratitis capitata, will provide tools to permit determination of source populations for new pest infestations. Restriction fragment length polymorphism (RFLP) of mitochondrial DNA provides some interpopulation discrimination. A restriction map, including the informative variableEcoRV andXbaI restriction sites, is constructed for the Mediterranean fruit fly, and several restriction sites are associated with specific gene regions based on polymerase chain reaction-RFLP and sequence analyses. A partial sequence of the mitochondrial 16S ribosomal RNA gene is reported.     

Learning to find fruit in Ceratitis capitata flies

Wild Mediterranean fruit fly females, Ceratitis capitata (Wiedemann), from an essentially monophagous population on the island of Hawaii were exposed to natural mock orange (Murraya paniculata) or sweet orange (Citrus sinensis) host fruit hung from branches of potted trees for 3-day periods in field enclosures. Subsequently, when flies were released individually onto potted trees harboring one or the other (or a mixture) of these fruit types, a higher proportion visited the type of fruit with which they were familiar (and visitors found familiar fruit faster) compared with the fruit type with which they were unfamiliar. Moreover, fruit-finding flies of this monophagous population attempted oviposition exclusively in the familiar fruit type, and thus appeared to be just as capable of learning to accept fruit for oviposition as wild flies from a previously-tested polyphagous population on the island of Maui. Additional tests were conducted in which flies were exposed to natural or colored-wax-covered mock oranges or sweet oranges and tested for response to colored-wax-covered natural or artificial fruit. Results suggested that fruit size was the principal character learned and used in finding mock orange or sweet orange fruit, while fruit color and odor appeared to be of little or no importance in this regard.

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Résumé Des femelles sauvages d'une population essentiellement monophage de C. capitata Wiedemann, provenant de l'île de Hawaï, ont été mises en présence pendant des périodes de 3 jours dans des enceintes dans la nature à des fruits de Murraya paniculata et de Citrus sinensis suspendus à des branches d'arbres empotés. Quand les mouches ont été libérées individuellement sur les arbres empotés portant l'un ou l'autre de ces fruits (ou leur mélange), une plus forte proportion a visité le fruit avec lequel elles étaient familiarisées (et l'ont trouvé plus vite) que le fruit avec lequel elles ne n'étaient pas. De plus, les femelles découvrant des fruits de cette population monophage ne tentèrent de pondre que dans le type de fruit avec lequel elle étaient familiarisées. Elles se montrèrent aussi capables que les mouches d'une population polyphage de l'île de Maui d'apprendre à accepter de nouveaux fruits pour pondre. Des expériences complémentaires ont été réalisées dans lesquelles les mouches étaient mises en présence de fruits de M. paniculata ou de C. sinensis naturels ou couverts de cire colorée ou encore de fruits artificiels. Les résultats suggèrent que la taille du fruit est le principal critère d'apprentissage utilisé pour trouver M. paniculata ou C. sinensis, la couleur et l'odeur du fruit étant apparus comme de moindre importance ou sans effet.

     

Recombination between homologous autosomes in medfly (Ceratitis capitata) males: type-1 recombination and the implications for the stability of genetic sexing strains

The sterile insect technique (SIT) is an environmentally safe technology to control insect pests. To improve this technology, genetic sexing strains (GSS) have been developed for the Mediterranean fruit fly, Ceratitis capitata. Such strains are based on Y-autosome translocations linking a selectable marker to the male sex and their long-term stability, especially under large-scale mass rearing conditions, is threatened by genetic recombination in the heterozygous males. We have measured male recombination in order to be able to construct GSS that are more stable. Our results show that male recombination occurs at very low frequencies, that is, below 1% per generation. Furthermore, recombination in medfly males occurs premeiotically. By selecting strains where the Y-autosome translocation breakpoint and the selectable marker are closely linked, the deleterious effects of recombination on the stability of GSS can be minimized. In such strains recombination is reduced by ca. 80% as compared to previously studied GSS. Although recombinants still occur at very low frequencies they still pose a threat to the integrity of the sexing system if they possess a selective advantage. Under mass rearing condition such recombinants will accumulate according to their relative fitness and additional measures, such as improved mass rearing strategies, are required to preserve the accuracy of the sexing system. As a conclusion it is shown that current GSS are stable enough to allow mass rearing at levels exceeding 1000 million male medflies per week.     

Electroantennogram responses of the Mediterranean fruit fly, Ceratitis capitata, to the volatile constituents of nectarines

Electroantennograms (EAGs) were recorded from laboratory-reared, male and female Ceratitis capitata (medfly) in response to individual volatiles identified from ripe nectarines. Uniformity in EAG response between the sexes was observed for most test compounds. Only 10 volatiles, of the 44 nectarine volatiles tested, elicited significantly different EAG responses between the sexes. No correlation was observed between the magnitude of antennal responsiveness and the concentration of a particular volatile in the headspace odor of ripe nectarines. The most abundant (major) nectarine volatiles were among the least EAG stimulatory compounds tested. And certain minor and trace volatiles were the most potent compounds in eliciting EAGs. Moreover, the magnitude of antennal response to a nectarine volatile was related to the functional-group, chain-length, and unsaturation of the compound. The degree of potency of the compounds was as follows: six-carbon unsaturated aldehydes and alcoholsmethyl and ethyl hexanoates and octanoateshexenyl acetates and monoterpenes>shorter chain-length acetates and alcohols>lactones. Unsaturated aldehydes, alcohols, and acetates generally elicited larger EAGs than their saturated analogs, with the (E)-2-isomers being the most potent isomeric configurations. In addition, medfly antennae exhibited long recovery periods (i.e., >10 sec.) for the EAG tracings to return to baseline potential after stimulations with certain classes of compounds, e.g., C₆ to C₈ acid esters, monoterpenes, and hexen-1-ols. The potential adaptiveness to medflies for selective sensitivity to these volatiles is discussed.     

Electroantennogram responses of the Mediterranean fruit fly, Ceratitis capitata to identified volatile constituents from calling males

Fifty-six compounds from the odor of calling, sexually mature, laboratory reared males of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) were isolated by headspace trapping on Tenax columns and identified using GC/MS techniques (69 total compounds were detected). Electroantennogram responses (EAGs) to 54 of the 56 identified compounds as well as 5 analogs were tested on both sexes. Significant differences between the sexes in their responsiveness were found in 9 of the 54 identified compounds tested. There was no correlation between the amplitude of the EAG response and the relative abundance of compound identified from headspace analysis. Of the five major identified components, three elicited relatively small EAG responses, while two elicited large EAGs compared to the hexan-1-ol standard. The relative ranking of EAG responses were: methyl and ethyl hexenoates and hexanoates > C₄–C₆ esters and/or acetates > ethyl and methyl octenoates > monoterpenes > sesquiterpenes > C₂–C₅ acetates, alcohols and ketones. Behavioral bioassays on each of the five major identified components as well as a blend of six of the compounds showed some degree of attractancy to virgin females which in some cases approached the response to a pheromonal standard (male odors absorbed onto filter paper). These results are discussed in relationship to the insect's antennal sensitivity to putative pheromone components and/or allomonal components and to other reported C. capitata pheromone studies.

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Résumé Cinquante-six composés de l'odeur de mâles de C. capitata Weidemann, élevés en laboratoire, sexuellement mûrs et en appel, ont été isolés par piégeage sur colonnes tenax et identifiés par la technique GC/MS (69 composés avaient été détectés en tout). Les électroantennogrammes (EAGs) ont été examinés chez les deux sexes pour 54 des 56 composés identifiés et 5 de leurs analogues. Des différences significatives entre les sexes ont été observées pour 9 des 54 composés identifiés. Il n'y avait pas de corrélation entre l'ampleur de l'EAG et l'abondance relative du composé lors de son isolement. Pour les 5 principaux composés identifiés, 3 ont induit des EAGs relativement faibles, tandis que 2 étaient importants, par comparaison avec l'Hexane-1-ol utilisé comme témoin. Le classement relatif des EAG a été: hexénoates et hexanoates d'éthyl et de méthyl C₄–C₆ esters et/ou acétates octénoates d'éthyl ou de méthyl monoterpènes sesquiterpènes C₂–C₅ acétates, alcools et kétones. Les expériences de comportement avec chacun des 5 composés principaux identifiés, comme avec des mélanges de 6 composés ont mis en évidence une attraction des femelles vierges qui dans quelques cas avoisine la réponse à la phéromone témoin (odeur du mâle absorbée sur papier filtre). Ces résultats sont discutés en fonction de la sensibilité de l'antenne d'insexte aux composés supposés de la phéromone et aux composés allomonaux, et en fonction des autres études connues sur les phéromones de C. capitata.

     

Life history response of female Mediterranean fruit flies, Ceratitis capitata, to periods of host deprivation

Female medflies were subjected to four different patterns of host deprivation at each of three levels for a 24-day period. Treatments ranged from host absence 8 days post-eclosion to host absence 2 out of 3 days. Survival was recorded daily and egg production was recorded on the days in which hosts were present.The direct effect of host deprivation is to deny females the opportunity to oviposit. This disrupts their reproductive cycle and reduces their overall reproductive effort. Reduced reproductive effort at young ages increases survival (up to 2-fold) and daily reproduction (up to 8-fold) at older ages. Therefore, the long term effect of host deprivation is to postpone senescence.The implications of these findings regarding medfly sensescence are discussed in relation to: (i) reduction in population extinction rates during periods of host scarcity and (ii) egging strategies in medfly mass-rearing.

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Résumé Les femelles de C. capitata ont été privées d'hôtes suivant 4 modalités pendant 3 durées (33, 50 et 67% de leur vie) par période de 24 heures. Les modalités se répartissaient de la privation pendant 8 jours après l'éclosion jusqu'à 1 jour sur 3. La survie a été notée chaque jour et la ponte pour tous les jours où il y avait des hôtes.L'effect direct de l'absence d'hôte est d'empêcher la femelle de pondre. Ceci interrompt leur cycle de ponte et réduit leur activité reproductrice totale. Un effort reproductif réduit des femelles jeunes augmente la survie (jusqu'à 2 fois) et la ponte quotidienne (jusqu'à 8 fois) chez les femelles plus âgées. Ainsi, l'effet à long terme de la privation d'hôtes est d'ajourner la sénescence.Les implications de ces observations sur la sénescence de C. capitata sont discutées quant à: (1) la réduction des taux d'extinction des populations pendant les périodes de rareté d'hôtes; et: (2) les stratégies d'obtention de pontes dan les élevages de masse de C. capitata.

     

Infestation rate of argan fruit (Argania spinosa) by the Mediterranean fruit fly (Ceratitis capitata) in relation to phenology and maturation of the fruit

Argan (Argania spinosa (Sapotaceae)) forest covers about 700,000 ha in the Souss region (Morocco). The medfly Ceratitis capitata Wiedemann (Diptera: Tephritidae) is known to develop in argans. In this study, we examine variations in medfly infestation rates according to argan phenology from 1987 to 1990. Argan phenology varies greatly among trees, total fruit drop spreading from late March to mid-July; moreover, an exceptional fructification may occur in Autumn in some trees. From February to about May, the infestation rate is low except in fruit produced during autumnal fructification. In June and July, the rate increases greatly reaching 100% in some trees. Ripe and ripening argans are the most heavily infested; only 10% of immature fruits on the average are attacked by the medfly. Fallen argans are more heavily infested than fruit still on the tree. Productivity per argan averaged from one to three adult medflies. Our results demonstrate that argan forest in the Souss acts as an enormous reservoir of medflies for the nearby citrus orchards.

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Résumé L'arganeraie (Argania spinosa) couvre environ 700000 ha dans la région du Souss, au Maroc. La mouche méditerranéenne des fruits, Ceratitis capitata, est connue pour se développer dans les arganes. Des études ont été menées, de 1987 à 1990, pour étudier comment le taux d'infestation des arganes variait selon leur degré de maturation. La phénologie des arganiers varie fortement selon les arbres: par exemple la chute totale des fruits s'étale de fin mars à mi-juillet. De plus, une fructification peut être observée en automne mais elle ne concerne qu'un nombre limité d'arbres. De février à mai environ, le taux d'infestation des arganes reste faible, sauf pour les fruits produits pendant la fructification de l'automne précédent. En juin en juillet, le taux augmente fortement atteignant 100% dans certains arbres. Les arganes mûres ou mûrissantes sont les plus attaquées; seuls 10% en moyenne des fruits immatures sont infestés. Les fruits tombés sont toujours (sauf à la fin) nettement plus attaqués que ceux encore présents dans l'arganier. De une à trois Cératites adultes sont formées à partir d'une argane. Nos résultats démontrent que la forêt d'argane du Souss constitue un réservoir gigantesque de la Cératite pour les infestations des vergers d'agrumes proches.

     

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.     

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.     

Gut bacterial communities in the Mediterranean fruit fly (Ceratitis capitata) and their impact on host longevity

Fruit flies (Diptera: Tephritidae) harbor stable bacterial communities in their digestive system, composed mainly of members of the Enterobacteriaceae. However, the Enterobacteriaceae are not the sole community in this habitat. We examined the hypothesis that Pseudomonas spp. form a cryptic community in the gut of Ceratitis capitata, the Mediterranean fruit fly (‘medfly’). Suicide polymerase restriction PCR (SuPER PCR), a novel culture-independent technique, revealed that Pseudomonas spp. form minor, common and stable communities within the medfly's gut. These include P. aeruginosa, a known pathogen of arthropods. Experimental inoculations with high levels of P. aeruginosa reduced the medfly's longevity while inoculations with members of the Enterobacteriaceae extended the fly's life.Accordingly, we suggest that in addition to their possible contribution to the fly's nitrogen and carbon metabolism, development and copulatory success (as shown in previous studies), the Enterobacteriaceae community within the medfly's gut may also have an indirect contribution to host fitness by preventing the establishment or proliferation of pathogenic bacteria.