Gérard Delvare

Abundance and stratification of foliage arthropods in a lowland rain forest of Cameroon

Abstract. 1 Arthropod densities and apparent leaf damage were compared within the canopy ecotone and the shrub layer of a lowland rain forest in Cameroon, using a branch clipping method. 2 Most of the individuals collected consisted of ants (average 44%) and various herbivores (31%). Overall arthropod densities amounted to 17 individuals per sample, which, on average, consisted of 0.85 m2 of foliage area. Arthropod densities were lower than on temperate foliage. 3 Arthropod densities were about 3 times higher in the canopy than within the shrub layer. In particular, ants and herbivores were significantly more abundant in the canopy than within the shrub layer. Usually, layer effects rather than site effects appeared to cause greater variance in arthropod abundance. 4 Arthropod species‐richness, as estimated by the number of operational taxonomic units sorted, was higher in canopy samples than in samples obtained from the shrub layer. However, apparent leaf damage was higher within the shrub layer (10.9%) than on the canopy (5.2%). 5 Possible factors responsible for the high densities of ants and herbivores on the canopy and for the high leaf damage within the shrub layer are discussed.

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

RésuméA 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 families 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 complete 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 ceuvre de stratégies de surveillance et d’intervention dans un secteur en constant développement pour l’économie insulaire.AbstractIn 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 beneficiais, 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.