Performance of augmentorium as a sanitation technique against fruit flies (Diptera: tephritidae) in Reunion Island

Background. Tephritid fruit flies cause severe damage to fruit and vegetable crops in Reunion Island. Instead of the curative approach to reduce existing populations, the first step proposed for their management is sanitation. This method is based on an original technique firstly developed by USDA in Hawaii utilizing a tent-like structure called an "augmentorium" which aims to sequester adult flies emerging from infested fruit while allowing the parasitoids to escape, via a net placed at the top of the structure. This study focused on the performance and the efficiency of the augmentorium prototype recently tested in Reunion Island and particularly (i) the number of adult flies that can potentially be sequestered in an augmentorium in the field; (ii) the efficiency of the net mesh for fly sequestration and parasitoid escape; (iii) the feasibility of producing compost with infested fruit collected in the field. Method. The potential number of flies that could be sequestered was estimated by measuring in the lab the emergence of several species of flies from infested fruit collected in the field from 2005 to 2009 in different sites of the island. Emergence of adult flies was measured for six species of flies: (i) Bactrocera cucurbitae, Dacus ciliatus and D. demmerezi attacking three species of Cucurbits (pumpkin: Cucurbita maxima; cucumber: Cucumis sativus and courgette: Cucurbita pepo); (ii) Bactrocera zonata, Ceratitis rosa and C. capitata attacking one species of fruit (mango: Mangifera indica). The sequestration of three of these fly species (B. cucurbitae, B. zonata and C. capitata) and the escape of two of their parasitoids (Psyttalia fletcheri and Fopius arisanus) were assessed in the Cirad laboratory in Saint-Pierre in 2008. Preliminary tests on the feasibility of producing compost were then conducted in Saint-Pierre in 2009, mixing courgette and other components. Results. Collections of infested fruits showed the following means of emerged adults per kg of fruit: 76 for mango (B. zonata, C. rosa, C. capitata); 217 for cucumber, 340 for pumpkin and 594 for courgette (B. cucurbitae, D. ciliatus, D. demmerezi). The efficiency of the mesh chosen for the prototype of augmentorium (hole area 1.96 mm²) proved to be perfectly effective in the lab with 100% of sequestration of adult flies. In the same way, 100% of the parasitoids were able to escape from the mesh if they choose to do so. In addition, we showed that a ratio of 50:30:20 of courgette, sugar cane stem and chicken litter respectively was well adapted to produce compost. Conclusion. These results confirm the relevance and the efficiency of the augmentorium in an agroecological crop protection. As a sanitation technique against fruit flies, the augmentorium sequesters on average several hundreds of adult flies per kg of infested fruit. As a biological control method, it may contribute to increase parasitoid populations which are often low because of the previous and significant pesticide pressure. The augmentorium can also be considered as a useful tool to produce compost in the context of sustainable agriculture. The technique of sanitation using the augmentorium is now well accepted by farmers in pilot areas in Reunion Island. (Texte intégral

Population structure and cryptic genetic variation in the mango fruit fly, Ceratitis cosyra (Diptera, Tephritidae)

The fruit fly Ceratitis cosyra is an important agricultural pest negatively affecting the mango crop production throughout Africa and also feeding on a variety of other wild and cultivated hosts. The occurrence of deeply divergent haplotypes, as well as extensive morphological variability, previously suggested possible cryptic speciation within C. cosyra. Here we provide the first large-scale characterisation of the population structure of C. cosyra with the main objective of verifying cryptic genetic variation. A total of 348 specimens from 13 populations were genotyped at 16 polymorphic microsatellite loci. Hardy-Weinberg equilibrium (HWE) deviations were observed in 40.4% of locus-population combinations and suggested the occurrence of genetic substructuring within populations. Discriminant Analysis of Principal Components (DAPC) showed genetic divergence between the vast majority of vouchers from Burundi and Tanzania (plus a few outliers from other African countries) and all other specimens sampled. Individual Bayesian assignments confirmed the existence of two main genotypic groups also occurring in sympatry. These data provided further support to the hypothesis that C. cosyra might include cryptic species. However, additional integrative taxonomy, possibly combining morphological, ecological and physiological approaches, is required to provide the necessary experimental support to this model. (Résumé d'auteur

Genetic diversity of Bemisia tabaci species colonizing cassava in Central African Republic characterized by analysis of cytochrome c oxidase subunit I

After 2007, upsurges of whiteflies on cassava plants and high incidences of cassava diseases were observed in Central African Republic. This recent upsurge in the abundance of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) was directly linked to serious damage to cassava crops resulting from spread of whitefly-borne cassava mosaic geminiviruses (CMGs). There is currently very little information describing whitefly populations on cassava and associated crops in Central African Republic. The current study aimed to address this gap, and to determine whether the increasing damage associated with B. tabaci whiteflies was the consequence of a new invasion, or an upsurge of a local population. The molecular genetic identification and phylogenetic relationships of 898 B. tabaci adult individuals collected from representative locations (54) throughout CAR were determined based on their mitochondrial cytochrome oxidase I sequences (mtCOI). Field and ecological data were also collected from each site, including whitefly abundance, CMD incidence, host plants colonized by B. tabaci and agro-ecological zone. Phylogenetic analysis of the whitefly mtCOI sequences indicated that SSA1 (-SG1, -SG2), SSA3, MED, MEAM1 and Indian Ocean (IO) putative species occur in CAR. One specific haplotype of SSA1-SG1 (SSA1-SG1-P18F5) predominated on most cassava plants and at the majority of sites. This haplotype was identical to the SSA1-SG1 Mukono8-4 (KM377961) haplotype that was recorded from Uganda but that also occurs widely in CMD pandemic-affected areas of East Africa. These results suggest that the SSA1-SG1-P18F5 haplotype occurring in CAR represents a recent invasive population, and that it is the likely cause of the increased spread and severity of CMD in CAR. Furthermore, the high mtDNA sequence diversity observed for SSA1 and its broad presence on all sites and host plants sampled suggest that this genetic group was the dominant resident species even before the arrival of this new invasive haplotype

Evolution of pesticide resistance in invasive versus indigenous agricultural pests in an insular tropical environment

Insular environments are among the most vulnerable ecosystems in the world, partly due to their small size and isolation. In La Reunion, an island in the southwest Indian Ocean, three whitefly species of the Bemisia tabaci (Gennadius) complex of cryptic species coexist: the indigenous species IO, and two exotic invasive species MEAM1 and Med, introduced in the late 1990s and in the early 2010s, respectively. B. tabaci is a major pest distributed worldwide, and a vector of plant viruses, responsible of serious damages on crops. The generalization of the use of pesticides has led to the emergence and rapid evolution of resistance in whitefly populations. In other countries, MEAM1 and Med have already demonstrated high resistance levels to all of the important classes of pesticides. Our objectives were to understand indigenous versus invasive whitefly species distribution in La Reunion, according to the different ecosystems; and how it could be linked to selection pressure of pesticide treatments. To assess species distribution, whiteflies were sampled at 59 collection sites, located all over the island in agroecosystems and natural areas. Molecular (kdr mutation, conferring Pyrethroid resistance) and laboratory bioassays (on three main classes of pesticides: Neonicotinoids, Pyridine azomethine derivatives and Pyrethroids) approaches were conducted on part of the sampled populations to assess pesticide resistance. The indigenous species IO was mainly sampled in natural areas and was found to be sensitive to the three classes of pesticides tested; in addition, no kdr mutation conferring Pyrethroid resistance was detected. The two exotic invasive species MEAM1 and Med were dominant in agrosystems. Most of the MEAM1 populations were found to be resistant to the three classes of pesticides tested, and kdr mutation was detected in both invasive species. Our results are in line with resistance cases reported worldwide in the literature, and suggest that whitefly species distribution in La Reunion could be driven by selection pressure of pesticide treatments

Unraveling the mysteries of honeybee in the Mascarene Islands

Exam paper for second semester 2017, N.D. Extraction Metallurg

Tritrophic interaction in the complexes of fruit flies damaging fruit and vegetable crops in Reunion island

The study of tri-trophic interactions is a vast field of basic ecological studies which are also of paramount importance for the development of environment-friendly methods of pest management. Within the Diptera, the Tephritidae family represents an interesting model for such studies because of the variable host-specificity of species in this group, and the important role that some natural enemies may play in the regulation of their populations. Furthermore, the great economic importance of many species in this family offers a large array of applications to research results. La Réunion, a French island situated in the south-west of the Indian Ocean, is a favourable area for studying such interactions, because of the number of tephritid species present in the island, and the great variability of its climatic conditions. On fruit crops, a complex of three polyphagous species of tephritids cause considerable damage: the Mediterranean fruit fly, Ceratitis capitata, the Natal fruit fly, Ceratitis rosa, and the Peach fruit fly, Bactrocera zonata. In addition, another complex of Dacini is harmful to cucurbit crops: the Melon fly, Bactrocera cucurbitae, the Ethiopian cucurbit fly, Dacus ciliatus, and the Indian Ocean cucurbit fly, Dacus demmerezi. Conversely, on Solanaceous crops such as tomato, the Tomato fruit fly Neoceratitis cyanescens, is the only species of economic importance. Over the last twenty years, many field studies allowed us to specify the host-range and relative importance of the different species on cultivated crops. Of particular interest are some host preferences observed in the field in some otherwise very polyphagous species, such as C. capitata. Detailed studies (lab, wind tunnel and field cages) were also devoted to the host location behaviour of stenophagous species, taking as a model the tomato fruit fly, N. cyanescens. Other behavioural studies also highlighted the preferences of the different species for particular host-plants during foraging or egg-laying behaviour. More recently, studies were focused on the quality of various host or non-host fruits for the pre-imaginal development of the different species, and its influence on their fitness. Though some indigenous parasitoids of the Mediterranean fruit fly have been recorded in the island, most of the natural regulation by parasitoids is due to exotic species imported through classical biological control programmes. This is particularly the case with two species imported from Hawaii, in collaboration with USDA Hawaii and the University of Hawaii: Psyttalia fletcheri, a larvo-pupal parasitoid of the Melon fly, and, more recently, Fopius arisanus, an egg-pupal parasitoid of some Bactrocera spp. Following the acclimatization of these two species, field studies allowed us to evaluate their host range, favourite habitats, and impact on host species populations. In addition, laboratory, field-cage and wind tunnel studies improved our knowledge of the stimuli involved in host habitat and host selection behaviours. Results of these studies are summarized and discussed in relation to the current state of knowledge of insect-plant and host-parasitoid interactions in tephritids, and to their possible applications in pest management. (Texte intégral

Genetic diversity and differentiation among insular honey bee populations in the southwest Indian Ocean likely reflect old geographical isolation and modern introductions

With globalization the Western honey bee has become a nearly cosmopolitan species, but it was originally restricted to the Old World. This renowned model of biodiversity has diverged into five evolutionary lineages and several geographic “subspecies.” If Apis mellifera unicolor is indubitably an African subspecies endemic to Madagascar, its relationship with honey bees from three archipelagos in the southwest Indian Ocean (SWIO) hotspot of biodiversity is misunderstood. We compared recent mtDNA diversity data to an original characterization of the nuclear diversity from honey bees in the Mascarenes and Comoros archipelagos, using 14 microsatellites, but also additional mtDNA tRNALeu-cox2 analysis. Our sampling offers the most comprehensive dataset for the SWIO populations with a total of 3,270 colonies from 10 islands compared with 855 samples from Madagascar, 113 from Africa, and 138 from Europe. Comprehensive mitochondrial screening confirmed that honey bees from La Réunion, Mauritius, and Comoros archipelagos are mainly of African origin (88.1% out of 2,746 colonies) and that coexistence with European lineages occurs only in the Mascarenes. PCA, Bayesian, and genetic differentiation analysis showed that African colonies are not significantly distinct on each island, but have diversified among islands and archipelagos. FST levels progressively decreased in significance from European and African continental populations, to SWIO insular and continental populations, and finally among islands from the same archipelago. Among African populations, Madagascar shared a nuclear background with and was most closely related to SWIO island populations (except Rodrigues). Only Mauritius Island presented clear cytoplasmic disequilibrium and genetic structure characteristic of an admixed population undergoing hybridization, in this case, between A. m. unicolor and A. m. ligustica, A. m. carnica and A. m. mellifera-like individuals. Finally, global genetic clustering analysis helped to better depict the colonization and introduction pattern of honey bee populations in these archipelagos. (Résumé d'auteur

What has changed in the outbreaking populations of the severe crop pest whitefly species in cassava in two decades?

High populations of African cassava whitefly (Bemisia tabaci) have been associated with epidemics of two viral diseases in Eastern Africa. We investigated population dynamics and genetic patterns by comparing whiteflies collected on cassava in 1997, during the first whitefly upsurges in Uganda, with collections made in 2017 from the same locations. Nuclear markers and mtCOI barcoding sequences were used on 662 samples. The composition of the SSA1 population changed significantly over the 20-year period with the SSA1-SG2 percentage increasing from 0.9 to 48.6%. SSA1-SG1 and SSA1-SG2 clearly interbreed, confirming that they are a single biological species called SSA1. The whitefly species composition changed: in 1997, SSA1, SSA2 and B. afer were present; in 2017, no SSA2 was found. These data and those of other publications do not support the ‘invader’ hypothesis. Our evidence shows that no new species or new population were found in 20 years, instead, the distribution of already present genetic clusters composing SSA1 species have changed over time and that this may be in response to several factors including the introduction of new cassava varieties or climate changes. The practical implications are that cassava genotypes possessing both whitefly and disease resistances are needed urgently