Evidence and population diversity of the rice yellow mottle virus (RYMV) insect vectors and some of their natural antagonists in paddy fields in the north of Cameroon

Abstract

From 2002 to 2004 two sampling methods were combined to assess the population of insects known as vectors of rice yellow mottle virus (RYMV) in the three major irrigated rice ecosystems in the north of Cameroon (Lagdo, Maga, Yagoua) and in lowland rice fields. Samplings were conducted by means of sweep net and D-Vac (the sucking trap) fortnightly in 2002 and 2003 until mid-October in lowland rice fields while in the irrigated fields, samplings occurred between December and April. Simultaneously, rearing on death concerned insects was conducted in the laboratory to identify the parasitoid insect species. From samples obtained at the different sites: (1) the dominant structure of the RYMV insect vectors was analysed according to the rice phenology; (2) the diversity and the occurrence of potential major groups of predators and parasitoids were assessed. Among the RYMV insect vectors sampled: Chaetocnema pulla Chapuis (Coleoptera: Chrysomelidae), Chnootriba similis Mulsant (Coleoptera: Coccinellidae), Trichispa sericea Guerin-Meneville (Coleoptera: Chrysomelidae), Locris rubra Fabricius (Hemiptera: Cicadellidae), Oxya hyla Stål (Orthoptera: Acrididae) and Conocephalus longipennis (de Haan) (Orthoptera: Tettigoniidae) were the most encountered insect species during the rice growing seasons. When investigating the arthropods acting in the rice fields as predators, spiders (Araneae) came at the top position with a high concurrency of Pardosa spp. (>42%) at all sites. At the sites Maga and Yagoua, the carabid beetles species Abacetus crenulatus Dejean and Abacetus foveolatus Chaudoir were the most numerous whereas the Lagdo site was highly colonised by Clivina erythropyga Putzeys, Paederus sabaeus Erichson and Stenus ravus Puthz were the most abundant staphylinid beetles. The rearing of dead RYMV insect vectors gave results on the emergence of the following parasitoids: Eurytoma spp., Pediobius spp., Tetrastichus spp., Telenomus spp.