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Landscape changes in a lowland in Benin: ecological impact on pests and natural enemies

Boucher A., Silvie P., Menozzi P., Adda C., Auzoux S., Jean J., Huat J.. 2015. Communications in Agricultural and Applied Biological Sciences, 80 (2) : p. 79-89. International Symposium on Crop Protection. 67, 2015-05-19/2015-05-19, Ghent (Belgique).

Habitat management involving conservative biological control could be a good crop pest management option in poor African countries. A survey was conducted from August 2013 to July 2014 in a rainfed lowland region near Pélébina, northern Benin, in order to characterize spatiotemporal lanscape changes and investigate their influence on the main crop pests and their associated natural enemies. The area was mapped mainly regarding crop fields and fallows. Visual observations were recorded and a database was compiled. Major landscape composition changes were noted between rainy and dry seasons, which affected the presence of both pests and natural enemies. Cereals (rice, maize and sorghum) and cotton were grown in the humid season, and then okra (Abelmoschus esculentus) was the dominant vegetable crop in dry season. These modifications impacted fallow abundance throughout the lowland. Different cotton (e.g. Helicoverpa armigera, Dysdercus sp., Zonocerus variegatus) or rice (e.g. Diopsis Iongicornis, D. apicalis) pests were observed during dry season in okra crops. Dry season surveys of Poaceae in two types of fallows ('humid', 'dry') revealed the presence of very few stem borers: only 0.004% of stems sampled were infested by stem borers, with a mean of 1.13 larvae per stem. Known cereal stem borer species such as Busseola fusca, Coniesta ignefusalis, Sesamia calamistis were not clearly identified among these larvae of their diapausing stage and white color. Unexpected pollinators (Hymenoptera Apidae, genus Braunsapis, Ceratina and Xylocopa) and predators (Crabronidae, genus Dasyproctus) were found in the stems. Sweep-net collection of insects in humid fallows allowed us to describe for the first time in Benin seven Diopsidae species (23% of adults bearing Laboulbeniomycetes ectoparasitic fungi). Some of these species were captured in rice fields during rainy season. Parasitoids (adult Chalcidoidae and Ichneumonoidae) were observed during both seasons but their impact on stem borers was hard to determine, even during the rainy season, due to their low abundance and the difficulty of identification. Predators (Reduviidae, Odonata) were found mainly in humid fallows and rice fields. Regarding our observations, we suggest the presence of alternate host crops such as okra during the dry season for rainy season crop pests. Moreover, fallows also had a real ecological role as a habitat resource for many guilds of insects (pollinators, pests, predators). The management of these landscape components should be the focus of a long-term study with the aim of enhancing pest management of rauny season crop pests.

Mots-clés : plante de culture; jachère; paysage agricole; ravageur des plantes; gestion intégrée des ravageurs; enquête organismes nuisibles; variation saisonnière; cartographie; lutte antiravageur; sorghum bicolor; oryza sativa; zea mays; abelmoschus esculentus; gossypium; dynamique des populations; Évaluation de l'impact; bénin

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