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.
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 life-history 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.
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.
Some species of fruit flies (Diptera: Tephritidae) shelter and roost in non-host plants surrounding crops. The aim of this study was to compare the attractiveness of two plants (Poaceae): maize,
Zea ...mays
(Linné) and Napier grass,
Pennisetum purpureum
(Schumacher) for two species of Dacini damaging cucurbits in Reunion Island:
Bactrocera cucurbitae
(Coquillett) (Diptera: Tephritidae) and
Dacus demmerezi
(Bezzi) (Diptera: Tephritidae). Plants of the two plant species were established in pots and presented to adult flies in field cages. In each cage, a cohort consisting of adults of a given species, of known sex and age, was released. For each species, the experiment was replicated four times. The number of adult flies on the different plants as well as their location on the plant was recorded. Maize was more attractive to adults of
B
.
cucurbitae
and
D
.
demmerezi
than Napier grass irrespective of sex and sexual maturity. Most adults of both species were found under the leaves of maize and Napier grass. The effects of the date, time of day, age, and sex of flies on their attraction to plants are discussed. A possible application of this study would be to use maize as a border plant to apply bait for the control of fruit flies.
Herbivorous insects searching for a host plant need to integrate a sequence of multimodal sensory inputs. We conducted a series of no-choice experiments in a laboratory wind tunnel to examine the ...behavioral response of the specialist fruit fly, Neoceratitis cyanescens (Diptera: Tephritidae), to host visual and olfactory stimuli presented singly or in combination (e.g., colored fruit model with or without host fruit odor). We also studied the influence of wind flow, age, and sex on the response of flies. In two-choice experiments, we evaluated the ability of mature females to discriminate between two fruit models emitting host vs. non-host fruit odor or clean air. Neoceratitis cyanescens mature females can use independently or interactively olfactory and visual stimuli to locate their host, whereas immature females and males respond primarily to host fruit odor. In the absence of wind, mature females mainly use visual information to locate the host fruit. In wind, host fruit odor significantly increases the probability and speed of locating the host fruit. In a two-choice situation between two bright orange spheres, flies accurately detected the sphere emitting host fruit odor vs. non-host fruit odor or odorless air. Nevertheless, they preferred to land on the bright orange sphere when the sphere emitting host fruit odor was blue. Furthermore, when odor source and fruit model were spatially decoupled (90 or 180°), >50% flies that landed on the fruit model initially performed an oriented flight toward the odor source, then turned back to the fruit model while in flight or after one landing, thus suggesting visual information to be the ultimate indicator of host fruit.
This paper reviews all available information regarding the occurrence and biology of the melon fly, Zeugodacus cucurbitae (Coquillett), in the Afrotropical Region, including data on invasion history, ...distribution patterns, population genetics, host range, and interspecific competition. Although limited intraspecific variability has been observed within the region regarding the above mentioned aspects, there seems to be no indication that Zeugodacus cucurbitae represents a species complex. A checklist of all of the species included in Zeugodacus as recently proposed by Virgilio et al. (2015) is provided.
Mature females of the tomato fruit fly Neoceratitis cyanescens can detect host fruit at a short distance using only visual stimuli, but little is known about the role of airborne volatile cues in the ...host searching strategy. A series of experiments is conducted in a laboratory wind tunnel, in which the behavioural responses of individual flies to volatiles from Solanaceae host plants (including tomato Lycopersicum esculentum Mill., bug weed Solanum mauritianum Scop. and Turkey berry Solanum torvum Sw.) are observed, according to some environmental (air speed) and physiological (age and mating status of females, time of day) factors. Mature females respond primarily to specific olfactory cues from blends of flowers or host fruit, preferentially unripe fruit for bug weed, as opposed to ripe fruit for Turkey berry or tomato. Males are also highly attracted by the odour of unripe fruit of bug weed. Wind plays a key role, as shown by the proportion of flies that reach the upwind section of the tunnel in the presence of both fruit odour and air flow (66.7%) and in the absence of either fruit odour (13.3%) or wind (36.7%). In response to fruit volatiles carried by wind, flies embark in a 'plume tracking' or 'aim and shoot' flight, consistent with odour-conditioned anemotaxis. Females respond to host fruit odour regardless of their age, egg load or mating status, and also more consistently in the afternoon, which is their preferential time of day for egg-laying. Searching behaviour and response to host volatiles in N. cyanescens are discussed in the light of host-finding and an adaptive strategy.
Phytophagous insects differ in their degree of specialisation on host plants, and range from strictly monophagous species that can develop on only one host plant to extremely polyphagous species that ...can develop on hundreds of plant species in many families. Nutritional compounds in host fruits affect several larval traits that may be related to adult fitness. In this study, we determined the relationship between fruit nutrient composition and the degree of host specialisation of seven of the eight tephritid species present in La Réunion; these species are known to have very different host ranges in natura. In the laboratory, larval survival, larval developmental time, and pupal weight were assessed on 22 fruit species occurring in La Réunion. In addition, data on fruit nutritional composition were obtained from existing databases.
For each tephritid, the three larval traits were significantly affected by fruit species and the effects of fruits on larval traits differed among tephritids. As expected, the polyphagous species Bactrocera zonata, Ceratitis catoirii, C. rosa, and C. capitata were able to survive on a larger range of fruits than the oligophagous species Zeugodacus cucurbitae, Dacus demmerezi, and Neoceratitis cyanescens. Pupal weight was positively correlated with larval survival and was negatively correlated with developmental time for polyphagous species. Canonical correspondence analysis of the relationship between fruit nutrient composition and tephritid survival showed that polyphagous species survived better than oligophagous ones in fruits containing higher concentrations of carbohydrate, fibre, and lipid.
Nutrient composition of host fruit at least partly explains the suitability of host fruits for larvae. Completed with female preferences experiments these results will increase our understanding of factors affecting tephritid host range.
In Reunion Island, the distribution of the domestic form of Aedes aegypti (L.) has been restricted to natural habitats, in ravines located on the driest west coast over the past 50 yr. It is mainly ...found in rock holes, where it principally co-occurs with Aedes albopictus (Skuse), the most common Aedes species and the major vector of arboviruses there. To document and understand the changes in Ae. aegypti distribution on the island since the beginning of the 20th century, data on its distribution from 1985 to 1986 and from 2007 to 2008 were analyzed and compared with previously published reports. The results show that the number of breeding sites with Ae. aegypti and the relative abundance of this species have progressively decreased and that this species is not found anymore in artificial containers. The causes of the decrease of Ae. aegypti populations are discussed. It is suggested that ecological factors such as a competitive interactions between Ae. aegypti and Ae. albopictus might have triggered the decrease of Ae. aegypti observed during the fifties and that vector control campaigns during these years might have accelerated this process.
The invasion of an established community by new species can trigger changes in community structure. Invasions often occur in phytophagous insect communities, the dynamics of which are driven by the ...structure of the host assemblage and the presence of competitors. In this study, we investigated how a community established through successive invasions changed over time, taking the last invasion as the reference. The community included four generalist and four specialist species of Tephritidae fruit flies. We analyzed a long-term database recording observed numbers of flies per fruit for each species on 36 host plants, over 18 years, from 1991 to 2009. Community structure before the last invasion by
in 2000 was described in relation to host plant phylogeny and resource availability. Changes in the host range of each species after the arrival of
.
were then documented by calculating diversity indices. The flies in the community occupied three types of niches defined on the basis of plant phylogeny (generalists, Solanaceae specialist, and Cucurbitaceae specialists). After the arrival of
.
, no change in the host range of specialist species was observed. However, the host ranges of two generalist species,
and
, tended to shrink, as shown by the decreases in species richness and host plant α-diversity. Our study shows increased host specialization by generalist phytophagous insects in the field following the arrival of an invasive species sharing part of their resources. These findings could be used to improve predictions of new interactions between invaders and recipient communities.
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