Potential for biological control of rice yellow mottle virus vectors

Abstract

Insect pests and disease infestations are the primary constraints in rice (Oryza sativa) production systems in Africa and Asia. For Cameroon in particular, the rice yellow mottle virus (RYMV) is increasingly a serious problem to rice production. During the poulations of the various insect vectors of RMYV are not known, and hence the need for this study. Unfortunately, 2002 - 2004, two sampling methods were combined to assess the population of insects vectors of rice yellow mottle virus (RYMV) in the three major irrigated rice ecosystems in northern Cameroon (Lagdo, Maga and Yagoua), and in low land rice fields. Sampling was conducted using sweep net and D-Vac (sucking trap) fortnightly in 2002 and 2003 until mid October in low land rice fields, while in the irrigated fields, samplings occurred between December and April. Rearing using dead insects was conducted simultaneously in the laboratory to identify the parasitoid insect species. From samples obtained at different sites: (i) the dominant structure of the RYMV insect vectors was analysed according to the rice phenology; and (ii) 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 Stal (Orthoptera: Acrididae), and Conocephalus longipennis (de Haan) (Orthoptera: Tettigoniidae) were the most encountered insect species during the rice growing seasons. With regard to predator populations, spiders (Araneae) were the most abundant, with high concurrency of Pardosa spp (> 42 %) in all sites. In Maga and Yagoua sites, the carabid beetle 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. From reared dead RYMV insect vectors, Eurytoma spp., Pediobius spp., Tetrastichus spp. and Telenomus spp. emerged as parasitoids. Results of this study reveal a great potential of biological control against rice yellow mottle virus vectors using predators and parastoids. This potential should be developed to manage the yield losses caused by the virus infection in rice cropping systems.