Essential oils of citrus fruit stimulate oviposition in the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae)

Female Mediterranean fruit flies (medfly) Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) perceive both qualitative and quantitative aspects of citrus fruit chemistry. However, the behavioural and biological adjustments of this response remain largely unknown. In the present study, the ovipositional responses of gravid female medflies to essential oils (i.e. the most critical resistance factor to medfly infestation) of various citrus fruits are investigated. In dual‐choice (treatment versus distilled water control) experiments, females lay significantly more eggs into pre‐punctured hollow oviposition hemispheres (domes) provided with 1 µL of citrus peel oil from sweet orange, satsuma mandarin, bitter orange, grapefruit and lemon compared with odourless domes. No‐choice tests show a weak effect of lemon essential oils in stimulating oviposition. The female ovipositional response to sweet orange oil (the most active in eliciting oviposition) is dose‐dependent. Additionally, limonene, the most abundant chemical in all citrus oils, stimulates oviposition, whereas linalool, a representative compound of immature citrus fruit associated with high toxicity against immature stages of fruit flies, has a significant deterrent effect. In further no‐choice tests, females lay approximately 23% fewer eggs in limonene (93%) (amount found in orange oil) and 60% fewer eggs in limonene 93% plus linalool 3% (approximately 10‐fold the amount found in orange oil) mixtures, relative to sweet orange oil. The results suggest that the limonene content accounts largely (but not completely) for the ovipositional responses observed in sweet orange oil, whereas high linalool proportions are capable of significantly masking and/or disrupting its stimulatory effects in citrus oils. The importance and practical implications of these findings with respect to understanding how citrus fruit chemistry influences the ovipositional responses of medfly is discussed.     

Effect of marking pheromone on clutch size in the Mediterranean fruit fly

Abstract Using acridine orange to selectively stain eggs, we showed that wild-collected female Mediterranean fruit flies (Ceratitis capitata Wiedemann) laid fewer eggs per clutch in fruit previously infested with eggs than in uninfested fruit. This effect is apparently attributable to marking pheromone deposited by females after oviposition: clutch size on fruit infested with eggs but free of marking pheromone was not statistically different from that on uninfested fruit. Clutch size on uninfested fruit on which marking pheromone was artificially transferred was significantly lower than that on uninfested and untreated fruit. Marking pheromone had a comparable though not statistically significant effect on the clutch size of females originating from a strain maintained in the laboratory for several hundred generations.     

地中海实蝇与植物检疫

地中海实蝇Ceratitis capitata (Wiedemann)是国际上十分重要的检疫性害虫,也是我国植物检疫工作中重要防御的检疫性害虫之一,近年来,从我国口岸检疫中共截获地中海实蝇12次。这充分表明了其潜在的危险性。为此,我国采取了一系列严格的检疫措施,有效地防止地中海实蝇传入。同时,为适应改革开放和国际贸易的发展,对检疫政策进行了调整,积极开展对水果、蔬菜的有害生物风险分析(PRA)研究工作,根据国际标准,划定非疫区范围,使植物检疫对贸易的不利影响降到最低限度,以促进水果、蔬菜进出口贸易的发展。     

Insecticidal and sublethal reproductive effects of Metarhizium anisopliae culture supernatant protein extract on the Mediterranean fruit fly

Because natural product‐based pesticides are thought to be more rapidly degradable than synthetic chemicals while having a lower ecotoxicological effect, the interest in these products for pest control has grown substantially. Recently, a new insecticide compound, which is the crude soluble protein extract (CSPE) from the fermentation product of the entomopathogenic fungus (EF) Metarhizium anisopliae (strain EAMa 01/58‐Su), has appeared in the literature as a promising insecticide for the control of the Mediterranean fruit fly, Ceratitis capitata. This CSPE has a moderate acute insecticide effect against adults of C. capitata when administered per os at 1 mg of protein/ml, as an exposure time of 8.3 h is necessary to get 50% of mortality. Even though the ingestion of this compound produces serious injuries in the midgut epithelium, it has a very low antifeedant effect on the flies. The effect of sublethal challenges on reproduction of adult flies was studied, and a reduction was found on the female fecundity levels during the first days after the treatment. On the other hand, the sublethal exposure to the CSPE affected neither the egg fertility nor the mortality of the larvae. However, the CSPE did affect the mortality of the pupae from the F1 generation, which suggests that there is a hormetic response from CSPE challenged females. The described sublethal reproductive effects are as important as direct lethal effects in contributing to the total value of the CSPE of the EF M. anisopliae 01/58‐Su strain.     

Infestation of fruit by conspecific and heterospecific females deters oviposition in two Tephritidae fruit fly species

Tephritidae fruit fly larvae develop entirely in the host chosen by the females. To improve the fitness of their progeny, females would benefit from rejecting previously exploited hosts. Anastrepha fraterculus and Ceratitis capitata are two species of fruit flies having similar nutritional requirements and overlapping in their distribution. Previous studies found that competition between the larvae of these species might reach high levels, suggesting that cross-recognition would be an adaptive trait. In this work, we tested the ability of A. fraterculus and C. capitata females to recognize and avoid fruits previously infested by both conspecific and heterospecific females. In laboratory behavioural arenas, females were presented with fruits that had been previously exposed to either conspecific or heterospecific females. Then, we conducted choice and non-choice assays to compare the response of A. fraterculus and C. capitata females to infested and non-infested fruits. In non-choice tests, the females from both species rejected fruits previously infested by conspecific and heterospecific individuals. However, the rejection occurred at different steps of the sequence leading to oviposition: A. fraterculus showed a lower rate of visits to infested fruits, whereas C. capitata visited both infested and non-infested fruits, but the latency to visit a fruit and the rejection frequency were higher and the duration of the visit to infested fruit was lower. In choice assays, the rejection of heterospecific infested fruit was higher than that of conspecific infested fruits, for both species. Our results suggest that, regardless of the sensory mechanism used by females, the recognition of previous infestation is bidirectional and females of both species, belonging to different genera, recognize fruit infested by heterospecifics. These responses indicate that cross-recognition, supposedly a highly beneficial trait, could be occurring in nature, thus reducing interspecific competition and contributing to the coexistence of these species.     

Use of fruit wounds in oviposition by Mediterranean fruit flies

Casual observations suggested that female Mediterranean fruit flies (Ceratitis capitata Wiedemann) exploit fruit wounds (including pre-existing oviposition punctures) as oviposition sites. This behaviour was quantified under field conditions in a citrus grove on the Greek island of Chios. Fruit wounds influenced oviposition behaviour in three ways. First, females were more likely to land on oranges (Citrus sinensis) that were artificially wounded than into unwounded control oranges. Second, having landed, females were more likely to attempt oviposition into a wounded orange than into control oranges. Third, females that attempted oviposition into wounded oranges usually did so directly into or very near the wound. The diameter and depth of the wound significantly influenced the tendency for female flies to land on a fruit but not their propensity, having landed, to attempt oviposition in or near the wound. The significance of this behavior in nature and implications for management of the Mediterranean fruit fly are discussed.

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Résumé Des observations fortuites nous ont suggéré que C. capitata Weidemann utilise les blessures des fruits, y compris d'anciennes piqûres de ponte, pour déposer ses oeufs. Ce comportement a été quantifié dans une orangeraie de l'île grecque de Chios. Les blessures des fruits influent sur la ponte de 3 façons. D'abord, les femelles atterissent plus fréquemment sur les oranges, Citrus sinensis, artificiellement blessées que sur les fruits intacts. Ensuite, après atterrissage, les femelles tentent plus souvent de pondre sur une orange blessée que sur des oranges intactes. Enfin, les femelles pondent directement dans la blessure ou à proximité. Le diamètre et la profondeur de la blessure influent sur la tendance à l'atterrissage, mais non sur les tentatives de ponte dans la blessure ou près d'elle. La signification de ce comportement dans la nature et ses conséquences sur la lutte contre C. capitata sont discutées.

     

Intron size polymorphism of the Adh1 gene parallels the worldwide colonization history of the Mediterranean fruit fly, Ceratitis capitata

The exon-primed intron-crossing (EPIC) PCR technique was used to analyse the size variation at the first intron of the Ceratitis capitata Adh ₁ gene. A total of 27 samples from 16 natural populations was analysed from five geographical regions in the species range: Africa, Mediterranean Basin, Latin America, Hawaii and Australia. The Adh ₁ first intron varies extensively in length with at least 18 size variants ranging from 1400 bp to 3450 bp. These variants can be grouped into four distinct size categories: short, medium, long and very long. The majority of these variants are present only in the African populations. Only a subset of the ancestral variants appear to have succeeded in migrating from Africa during the medfly colonization process. The medfly population structure inferred from the intron size polymorphism is congruent with that observed from the analysis of allozyme variation. The geographical dispersal of the medfly from its source area is associated with a gradual and great reduction in intron variability which parallels the trend of decreasing variability evaluated at 26 biochemical loci. The intron phylogenetic tree is in agreement with allozyme data in portraying the dynamic population history of the medfly. Stochastic evolutionary forces such as drift, bottleneck effects and migration seem to have played the major roles in the dispersion pattern of Adh ₁ intron variation during the colonization of the medfly.     

Spatial patterns of sterile Mediterranean fruit fly dispersal

The success of the sterile insect technique (SIT) for the control of the Mediterranean fruit fly or medfly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), depends largely on the ability of sterile flies to spread in the target area and compete with the wild males for wild females. Our objectives in the present study were three‐fold: (1) to evaluate the dispersal ability of sterile male medflies and compare their spatial dispersion patterns with that of wild males, (2) to evaluate how different release methods affect subsequent spatial dispersal, and (3) to determine whether manipulating the pre‐release diet of sterile males affects their dispersal. To achieve these objectives, we conducted three experiments in the field where we quantified and analyzed the spatial and temporal dispersal patterns of sterile medflies and the dispersion of resident wild males. Overall, ca. 5% of the released sterile flies were recaptured 100 m from the release point, and ca. 2% were recaptured 200 m from the release point. The released flies rarely survived longer than 5–7 days. We repeatedly found that the spatial dispersion patterns of sterile males significantly correlated with those of wild males. Release methods strongly affected subsequent fly dispersal in the field as significantly more flies were recaptured following a scattered release vs. a central one. Finally, we show that enriching sterile fly pre‐release diet with protein did not affect subsequent dispersal in the field. We conclude that sterile males are able to match the dispersion patterns of wild males, an outcome that is highly important for SIT success. Large releases from central points distant from each other may leave many areas uncovered. Accordingly, scattered releases, repeated twice a week, will provide better coverage of all available aggregations sites. The spatial performance of protein‐fed males suggests that pre‐release diet amendments may be used without detriment as a sexual stimulant in SIT programs.     

cDNA cloning, characterization, and developmental expression of the 20S proteasome alpha5 subunit in the Mediterranean fruit fly Ceratitis capitata

In the present study, we report the cDNA cloning, characterization, and developmental expression of the 20S proteasome alpha5 subunit from the Mediterranean fruit fly Ceratitis capitata (medfly). Using an RT-PCR fragment that corresponds to the amino-terminal region of the Drosophila melanogaster 20S proteasome alpha5 subunit, we isolated a 987-bp cDNA that encodes the complete coding region of the medfly ortholog, which was named CcPSMA5. CcPSMA5 consists of 241 amino acids and has a predicted molecular weight of 26.4 kDa and pI 4.75. Comparison of the CcPSMA5 amino acid sequence with the sequences of all known 20S proteasome alpha5 subunits from different organisms indicated that the medfly 20S proteasome alpha5 subunit has the strongest homology to that of Drosophila. In situ hybridization showed that the CcPSMA5 gene is mapped in the region 44B of chromosome 4. Northern blot hybridization analysis showed that the CcPSMA5 mRNA has a size of approximately 1.2 kb. High levels of the CcPSMA5 mRNA were detected in freshly laid eggs, indicating that they were maternally deposited. The mRNA expression pattern during medfly development suggests that the CcPSMA5 gene is upregulated before mid-embryogenesis and at the onset of metamorphosis.     

Mate choice by wild and mass‐reared females of the Mediterranean fruit fly

The sterile insect technique (SIT) is used to control Mediterranean fruit fly, Ceratitis capitata (Wiedemann), but its effectiveness is limited by low sexual competitiveness of mass‐reared males. This study investigated whether wild and mass‐reared [from a temperature sensitive lethal (tsl) genetic sexing strain] females display similar mate preferences and thus exert similar selective forces on the evolution of male courtship behaviour. Wild females preferred wild males over tsl males, whereas tsl females mated indiscriminately. The probability that mounting resulted in copulation was related to the duration of pre‐mount courtship for wild females, and wild males performed longer courtships than tsl males. Copulation occurred independently of courtship duration in tsl females. Counter to the aim of the SIT, female choice by tsl females appears to promote the evolution of male behaviour disfavoured by wild females.     

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.     

Host-marking pheromone and use of previously established oviposition sites by the mediterranean fruit fly (Diptera: Tephritidae)

Under controlled conditions, the Mediterranean fruit fly, Ceratitis capitata(Wiedemann) preferred to initiate oviposition into preexisting, naturally formed oviposition punctures in a host fruit, kumquat (Fortunella japonica),over establishing new sites on the fruit. This preference was expressed despite the presence of naturally deposited host-marking pheromone (HMP)shown previously to deter oviposition. An almost-identical preference for existing punctures was expressed when females were presented with fruit bearing artificially made punctures on which HMP had been naturally deposited. Using artificial punctures and HMP extracts, the occurrence of punctures was manipulated independently of the presence of HMP.Under field-cage conditions, we found that (1) punctures stimulated egg-laying on kumquats, regardless of HMP treatment; (2) HMP extract inhibited egg-laying, regardless of the occurrence of punctures; and (3) the extent to which HMP inhibited egg-laying was greater on fruit free of punctures than on fruit bearing them. The physiological, evolutionary, and pest management implications of these results are discussed.     

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.     

Bringing back the fruit into fruit fly-bacteria interactions

Female Mediterranean fruit flies ( Ceratitis capitata ) oviposit in fruits, within which the larvae develop. This development is associated with rapid deterioration of the fruit, and frequently with invasion by secondary pests. Most research on the associations between medflies and microorganisms has focused on the bacteria inhabiting the digestive system of the adult fly, while the role of the fruit in mediating, amplifying or regulating the fruit fly microflora has been largely neglected. In this study, we examine the hypothesis that the host fruit plays a role in perpetuating the fly-associated bacterial community. Using direct and cultured-based approaches, we show that this community is composed in its very large majority of diazotrophic and pectinolytic Enterobacteriaceae. Our data suggest that this fly-associated enterobacterial community is vertically transmitted from the female parent to its offspring. During oviposition, bacteria are transferred to the fruit, establish and proliferate within it, causing its decay. These results show that the host fruit is indeed a central partner in the fruit fly–bacterial interaction as these transmitted bacteria are amplified by the fruit, and subsequently maintained throughout the fly's life. This enterobacterial community may contribute to the fly's nitrogen and carbon metabolism, affecting its development and ultimately, fitness.     

Molecular structure of yoyo, a gypsy-like retrotransposon from the Mediterranean fruit fly, Ceratitis capitata

We have isolated and characterized a new LTR-retrotransposon in the genome of the Mediterranean fruit fly (Medfly), Ceratitis capitata. This retrotransposon, which we named yoyo, appears to be a member of the gypsy/Ty3 class of elements. The yoyo element was originally discovered on the Y chromosome of the Medfly. Although the Y chromosome copy appears to be truncated, at least two other apparently complete copies of yoyo from other genomic locations have been isolated and characterized. The complete element is approximately 7.7 kb in size. In addition to fairly typical GAG and POL coding regions, the yoyo element contains a potential ENV gene. The presence of an ENV gene is a key feature distinguishing potential retroviral-like elements, such as gypsy (and possibly yoyo), from many other invertebrate retrotransposons previously described. In addition to the structural features of yoyo, evidence is provided to show that yoyo is capable of movement in the genome, including RFLPs showing variability in genomic localization of copies of yoyo between strains, and differences among individuals in the presence of yoyo at a specific site in the genome. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of egg load on finding and acceptance of host fruit in Ceratitis capitata flies

Abstract. In studies conducted on potted host trees in field cages and in the laboratory, we examined the influence of egg load on the finding and acceptance of high-ranking (kumquat) and lower-ranking (grapefruit) hosts for oviposition by wild-origin Mediterranean fruit fly females, Ceratitis capitata (Wiedemann). By prescribing the periods during which females had access to protein prior to testing, we generated four classes of females having progressively increasing egg loads but not differing in population origin, age, degree of protein hunger at testing, or amount of prior experience with host fruit (none). Egg load had no discernible effect on behaviour associated with finding either type of fruit but did have a significant effect on several behaviours associated with oviposition after alighting on fruit. Increasing egg load led to increasing propensity to engage in ovipositional-type behaviour on both kumquats and grapefruits. There was no evidence, however, to support a hypothesis that medflies would become less discriminating against grapefruits relative to kumquats as egg load increased. Relative to kumquats, grapefruits were accepted for oviposition by intermediate and high egg load females to a substantially greater degree in laboratory cages than on trees, suggesting that results of laboratory cage experiments on host discrimination by tephritid flies may poorly reflect differences in behavioural responses expressed under less constrained conditions.     

Changes of protein tyrosine phosphorylation in third instar larval integument of the Mediterranean fruit fly, Ceratitis capitata

Developmental analysis of the tyrosine protein phosphorylation levels in larval integument and partial characterization of the endogenous protein tyrosine kinase activity (PTK) in Ceratitis capitata are described in this study. Larval integument contains high levels of PTK activity at the early stages of the third instar, which progressively declines to low levels in the white pupal stage. An integumental 90-kDa polypeptide was identified to have prominent endogenous PTK activity and follow a similar developmental pattern. The major integumental phosphotyrosine-containing polypeptides have apparent molecular weights of 30, 41, 44, 46, and 54 kDa, respectively. Polypeptides with molecular weights of 62 and 73 kDa were identified as Ser/Thr-containing phosphoproteins and were shown to exhibit high levels of phosphorylation at the middle stage of larval development. These differences are likely to be due to the higher activation state of the protein tyrosine kinase(s) at the early stages of larval development.     

Fluctuating asymmetry and sexual selection in the Mediterranean fruitfly (Diptera, Tephritidae)

Sexual selection is known to operate at medfly leks with a few males gaining a high proportion of matings. However, specific male characteristics subject to sexual selection have not been identified. Here we report laboratory studies indicating that directional sexual selection operates on the level of fluctuating asymmetry (FA) in the superior frontal orbital setae (sex setae), with symmetrical males gaining more matings. Studies relating mating success with FA in a male trait have generally been taken as evidence of the operation of indirect sexual selection. For a male trait to acts as a reliable indicator of fitness, FA in the male trait should be negatively associated with trait size and females should mate with the males with the most exaggerated form of the trait. However no association was found between seta FA and mean seta length. In addition sexual selection did not appear to operate on mean trait size, although males with an intermediate sex seta to wing length ratio did achieve higher mating success, indicating that stabilizing sexual selection operates on this relative dimension. It is suggested that differences in male competitive ability may provide an alternative explanation of how such associations between mating success and FA in male characteristics can arise.     

Detection of novel mitochondrial haplotype variants in populations of the Mediterranean fruit fly,Ceratitis capitata,from Tunisia,Israel and Morocco

The direct analysis of DNA sequence‐based mitochondrial haplotypes in individuals from populations of the Mediterranean fruit fly, Ceratitis capitata, from Tunisia, Morocco and Israel has revealed levels of genetic diversity that far exceed those previously described. A total of 33 distinct haplotypes were identified from 117 individuals representing seven populations from these countries. A network of haplotypes was constructed showing that we have captured essentially all of the sequence variations present in these populations for this gene. These results have important implications for future studies of the genetic structure of this and other closely related pest species.     

Genetic relationships of populations and the origins of new infestations of the Mediterranean fruit fly

A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) approach based on the variation in intron sequences of the glucose-6-phosphate dehydrogenase (Zw) gene was used to assess genetic variability in 26 populations and infestations of the Mediterranean fruit fly (medfly), Ceratitis capitata. Beginning with the exon-primed intron-crossing PCR (EPIC-PCR) method to amplify introns of this gene, five alleles were identified on the basis of DNA sequence variants. Several of these variants affect recognition sites for the restriction enzymes RsaI and TaqI. Using these enzymes in successive digestions of the EPIC-PCR products, each of these alleles can be identified directly from individuals. From this, surveys were conducted to document genotypes and allele frequencies in these samples. The relationships of existing populations and the invasion process represented by new infestations of the medfly were analysed using a principal coordinate analysis and the amova method to quantify the distribution of genetic diversity at different levels in a hierarchical manner. From these results, a framework of genetic relationships among the populations and infestations is presented. In addition, for at least some of the infestations, populations that are probably acting as sources of origin have been identified.