Abstract. 1. A number of invasions in the family Tephritidae (fruit flies) have been observed worldwide despite quarantine procedures. In this review, the potential importance of interspecific competition and competitive displacement among different tephritid species is evaluated in the context of recent invasions.2. Where polyphagous tephritid species have been introduced in areas already occupied by a polyphagous tephritid, interspecific competition has resulted in a decrease in number and niche shift of the pre-established species. No reciprocal invasions have been observed.3. The data on tephritid invasions seem to support a hierarchical mode of competition; however, complete exclusion usually did not occur. Indeed, tephritid distribution and abundance are markedly structured by various abiotic (mostly climatic) and biotic (host plants) factors.4. The primary determinant of competitive interactions in near-optimal conditions, such as lowlands with abundant fruit plantations, is probably the lifehistory strategy. The r-K gradient could be used as a predictor of potential invaders, because K traits (such as large adult size) may favour both exploitation and interference competition.5. For future research, a better understanding of competition mechanisms seems essential. Different species competing in the same area should be compared with respect to: (i) demographic parameters, (ii) the outcome of experimental co-infestations on the same fruit, and (iii) behavioural and chemical interference mechanisms.

Fruit flies (Diptera: Tephritidae) are the most damaging pests on fruit crops on Réunion Island, near Madagascar. Survival and development of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), the Natal fruit fly, C. rosa Karsch and the Mascarenes fruit fly, C. catoirii Guérin-Mèneville were compared at five constant temperatures spanning 15 to 35 degrees C. Durations of the immature stages of C. capitata, C. rosa and C. catoirii ranged from 14.5-63.8, 18.8-65.7 and 16.8-65.8 days, respectively, at 30-15 degrees C. The lower developmental threshold and thermal constant were calculated using the temperature summation model. The thermal constant for total development of the immature stages of C. capitata, C. rosa and C. catoirii were 260, 405 and 356 DD, respectively. Species differed mainly during the larval stages and ovarian maturation period, with smaller differences in the egg stage. Ceratitis rosa appeared to be better adapted to low temperatures than the two other species as it showed a lower larval developmental threshold of 3.1 degrees C compared to 10.2 degrees C for C. capitata and 8.9 degrees C for C. catoirii. Overall, C. catoirii had a low survival rate within the range of temperatures studied. The different responses of the three Ceratitis species to various temperatures explain to some extent their distribution on the island. The results obtained will be used for optimizing laboratory rearing procedures and for constructing computer simulation models to predict fruit fly population dynamics.

Reunion Island suffers from high densities of the chikungunya and dengue vector Aedes albopictus. The sterile insect technique (SIT) offers a promising strategy for mosquito-borne diseases prevention and control. For such a strategy to be effective, sterile males need to be competitive enough to fulfil their intended function by reducing wild mosquito populations in natura. We studied the effect of irradiation on sexual maturation and mating success of males, and compared the sexual competitiveness of sterile versus wild males in the presence of wild females in semi-field conditions. For all untreated or sterile males, sexual maturation was completed within 13 to 20 h post-emergence and some males were able to inseminate females when 15 h old. In the absence of competition, untreated and sterile males were able to inseminate the same number of virgin females during 48 h, in small laboratory cages: an average of 93% of females was inseminated no matter the treatment, the age of males, and the sex ratio. Daily mating success of single sterile males followed the same pattern as for untreated ones, although they inseminated significantly fewer females after the ninth day. The competitiveness index of sterile males in semi-field conditions was only 0.14 when they were released at 1-day old, but improved to 0.53 when the release occurred after a 5-day period in laboratory conditions. In SIT simulation experiments, a 5∶1 sterile to wild male ratio allowed a two-fold reduction of the wild population’s fertility. This suggests that sterile males could be sufficiently competitive to mate with wild females within the framework of an SIT component as part of an AW-IPM programme for suppressing a wild population of Ae. albopictus in Reunion Island. It will be of interest to minimise the pre-release period in controlled conditions to ensure a good competitiveness without increasing mass rearing costs.

Summary 1.Biological invasions have profound effects on community structure. The community composition following invasions can be influenced by the habitat diversity and the species' responses to abiotic factors. 2. We evaluated the tolerance to climatic factors and analysed the field distribution of four polyphagous fruit flies (Diptera: Tephritidae) of La Réunion Island (three exotic species that successively invaded the island and the endemic species Ceratitis catoirii ) in order to evaluate the opportunities of coexistence by niche differentiation. 3. Atmospheric humidity and immersion in water in the laboratory greatly influence the survival of fruit fly pupae. While C. catoirii and C. rosa are very sensitive to desiccation, C. capitata and especially Bactrocera zonata are relatively tolerant. B. zonata also tolerated immersion in water much longer than did C. rosa and C. catoirii , that in turn were more resistant than C. capitata . Overall, field distributions agree with the predictions based on this study of humidity combined with previous data on the effects of temperature. 4. Climatic niche partitioning promotes coexistence between some but not all pairs of invasive species. Thus, C. rosa can coexist with both C. capitata and B. zonata at the regional scale, while climatic niches are not different enough to promote coexistence of the latter two species. The endemic species has no private climatic niche either and this now very rare species could be in the process of extinction. 5. By promoting coexistence or not, climatic diversity in invaded areas can directly affect the community composition following invasions.

Understanding the strength and modes of interspecific interactions between introduced and resident species (native or previously introduced) is necessary to predict invasion success. We evaluated different mechanisms of interspecific competition among four species of polyphagous fruit flies (Diptera: Tephritidae) from the island of La Reunion: one endemic species, Ceratitis catoirii, and three exotic species, C. capitata, C. rosa, and Bactrocera zonata, that have successively invaded the island. Larval competition experiments, i.e., co-infestations of the same fruit, and behavioral interference experiments measuring the ability of one female to displace another from a fruit, were performed among all pairs of the four species. We observed asymmetric and hierarchical interactions among species in both larval and adult interference competition. In agreement with the hypothesis that invasion is competition-limited, the competitive hierarchy coincided with the temporal sequence of establishment on the island, i.e., each newly established species tended to be competitively dominant over previously established ones.

The 'Ceratitis FAR complex' is a species complex of African fruit flies (Diptera, Tephritidae) including the major agricultural pest Ceratitis rosa and the morphologically similar Ceratitis fasciventris and Ceratitis anonae. To resolve their intra- and interspecific genetic relationships and to estimate gene flow within this complex, we surveyed allelic variation at 16 microsatellite loci in 27 African populations of the three morphospecies. Interpopulation genetic distances and individual Bayesian assignments distinguished five genotypic clusters: two involving C. rosa (R1, R2; that may occur in sympatry), two involving C. fasciventris (F1, F2; with parapatric distributions) and one involving C. anonae (A). Intra- and interspecific patterns of genetic differentiation were not hierarchically structured and genetic differentiation between conspecific clusters (F1-F2 and R1-R2) was higher or comparable with differentiation between heterospecific clusters (e.g. F1-A or R2-A). In some cases, gene flow estimates among morphospecies or among heterospecific genotypic clusters were significantly different from zero, showing the lack of reproductive isolation. Genetic differentiation between genotypic clusters was partly supported by morphological differences observed a posteriori in male secondary sexual characters. These results suggest important revisions to current models of ecological niche requirements and invasion risk of the major agricultural pest C. rosa and provide a basis for a taxonomic re-interpretation of the FAR complex.

Biological invasions generally induce profound effects on the structure of resident communities. In Mayotte, where Aedes aegypti and Ae. lilii were already present, the recent introduction of Ae. albopictus raises public health concerns because it may affect the risk of arbovirus transmission. Entomological surveys were carried out in six locations on the island following a transect defined by a gradient from urban to rural habitats during a dry and a wet season. A total of 438 larval habitats containing Aedes spp. immature stages were surveyed. We evaluated the characteristics of larval habitats and analyzed the field distribution of Aedes spp. throughout Mayotte using generalized linear models. Artificial containers used for water storage were significantly more productive for Ae. albopictus immature stages than for Ae. aegypti ones. Most of natural larval habitats collected were colonized by Ae. aegypti, and it was also the most common Aedes species encountered in rural habitats. Conversely, Ae. albopictus greatly predominated in urban and suburban habitats and during the dry season. Ae. lilii was uncommon and occurred preferentially in leaf axillae and dead leaves on the ground. Ae. albopictus has rapidly colonized the inhabited areas of Mayotte. A displacement of Ae. aegypti populations by Ae. albopictus populations in urban areas might be happening. The increasing urbanization seems to greatly favor the presence of the invasive species. Thus, arbovirus surveillance programs should focus, as a priority, on areas where this vector is present because of a higher risk of emergence of an epidemic source of arboviruses.

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