Ecological niche and potential geographic distribution of the invasive fruit fly *Bactrocera invadens* (Diptera, Tephritidae)

Two correlative approaches to the challenge of ecological niche modeling (genetic algorithm, maximum entropy) were used to estimate the potential global distribution of the invasive fruit fly, Bactrocera invadens, based on associations between known occurrence records and a set of environmental predictor variables. The two models yielded similar estimates, largely corresponding to Equatorial climate classes with high levels of precipitation. The maximum entropy approach was somewhat more conservative in its evaluation of suitability, depending on thresholds for presence/absence that are selected, largely excluding areas with distinct dry seasons; the genetic algorithm models, in contrast, indicate that climate class as partly suitable. Predictive tests based on independent distributional data indicate that model predictions are quite robust. Field observations in Benin and Tanzania confirm relationships between seasonal occurrences of this species and humidity and temperature

Host plant range of a fruit fly community (Diptera: Tephritidae): Does fruit composition influence larval performance?

Background: 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. Results: 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. Conclusion: 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. (Résumé d'auteur

Review Article - Inventaire Preliminaire des Arthropodes Ravageurs et Auxiliaires des Cultures Maraicheres sur l'Ile de la Réunion

In Reunion Island, insect and mite pests are significant limiting factors to the development of market crops. Several studies have been carried out on some families of pests during the last 40 years, but no comprehensive survey has been undertaken on the arthropods of vegetable crops on this island. During 1997/1998, we studied the arthropod complex on eight main families of crops, namely Solanaceae, Cucurbitaceae, Brassicaceae, Fabaceae, Liliaceae, Asteraceae, Apiaceae and Rosaceae. During a complete year of collection, we gathered 123 species of pests, including 114 species of insects and 9 of mites. We also identified a total of 128 species of beneficials, including 51 species of parasitoïds and 77 species of predators and consisting of 101 species of insects, 14 of mites and 13 of arachnids. Our data constitute the first step for the implementation of strategies for pest monitoring and integrated pest management in an important sector for the island's insular economy. RÉSUMÉ A la Réunion, les ravageurs des cultures maraîchères, insectes et acariens, constituent un facteur limitant important pour le développement de ces productions. De nombreuses études ont été faites sur certains groupes de ravageurs dans les quarante dernières années mais aucun travail d'ensemble n'avait été entrepris concernant les arthropodes de l'île de la Réunion. Les principales familles de cultures maraîchères inventoriées sont les Solanaceae, les Cucurbitaceae, les Brassicaceae, les Fabaceae, les Liliaceae, les Asteraceae, les Apiaceae et les Rosaceae. Le résultat de ce travail d'enquête sur une année complète a permis d'identifier 123 espèces de ravageurs dont 114 d'insectes et 9 d'acariens. Il a permis également de mettre en évidence 51 espèces de parasitoïdes et 77 espèces de prédateurs, soit un total de 128 espèces d'auxiliaires dont 101 d'insectes, 14 d'acariens et 13 d'arachnides. Les données recueillies constituent le préalable pour la mise en oeuvre de stratégies de surveillance et d'intervention dans un secteur en constant développement pour l'économie insulaire

Whole-farm nitrogen cycling and intensification of crop-livestock systems in the highlands of Madagascar:an application of network analysis

Food insecurity, soil fertility depletion and strong competition for biomass are commonly observed in smallholder crop-livestock systems. The objective of this study was to explore options to improve farm-level nitrogen cycling, productivity and economic performance through the analysis of N flows within four contrasting crop-livestock farm systems of Madagascar highlands. Farms were conceptualized as networks where the compartments were the household and their farming activities, all connected by N flows. Indicators assessing network size and cycling, and the organization and diversity of the N flows, were compared with system productivity, food self-sufficiency, and gross margins for the current situation and under four scenarios of intensification (i) dairy production increased by increasing N inputs as supplementary feed; (ii) crop production increased by increasing N inputs as mineral fertilizer; (iii) manure management improved to increase N conservation during storage and application to soils; (iv) a combination of the two most economically attractive scenarios (i and iii). The four case study farms represent local diversity differing widely in terms of network size, with total annual system N throughput ranging from 113 to 1037kgN per capita, and in terms of N cycling, from 3 to 41kgN per capita per year. They differed less in terms of external dependence, from 0.26 to 0.41kgN kgN-1. Improving N conservation through improved manure management (scenario iii) had a positive impact on gross margin, and this in combination with increased concentrate supply (scenario iv) led to increases in whole-farm N use efficiencies from 2% to 50%, in N cycling from 9% to 68% and in food self-sufficiency from 12% to 37% across farm types. Gross margin was the most sensitive indicator to changes in management. Intensification through scenario iv had the highest impact on farm productivity, gross margin, food self-sufficiency, and environment sustainability (N use efficiency, capacity of the soil to stock N)