Relationship between insect vectors abundance and occurrence of rice yellow mottle virus in farmers’ fields in Kilombero district

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Sokoine University of Agriculture


Rice yellow mottle virus (RYMV) endemic to Africa is spread within and between rice fields by several species of Chrysomelid beetles and grasshoppers. In Tanzania and particularly in Kilombero District, the virus is increasingly becoming a serious problem to rice production. The relationships between the insect vectors and RYMV disease incidence and severity were not fully known hence the need for this study. The assessment of both disease incidence and severity of RYMV and population abundance of its insect’s vectors were conducted in the three divisions of Mngeta, Ifakara and Mang’ula in Kilombero District, Tanzania in 4m2 quadrat. Insect sampling was conducted using sweep net while RYMD incidence and severity were visually assessed in a 4 m 2 quadrat. Results of the insect identification indicated the presence of two insect vectors of RYMV i.e. (Chaetocnema spp. and O. hyla). The population densities of these RYMV vectors were higher at the border parts of the rice fields than at the middle parts. On the other hand, the incidence and severity of RYMV disease increased with the age of the crop. Results of within field distribution also indicated a random distribution of RYMV-affected plants in the rice fields in the agro ecosystem. The field studies of the virus–vector relationship established that RYMV occurrence varied in space and time and crop development stages. The partial correlation analysis showed a positive relationship between insect vector’s population density and the incidence and severity of RYMVD. The two insect species were tested for their ability to transmit RYMV and both were able to transmit the virus from RYMV-infected plants to healthy rice seedlings suggesting their potential contribution to RYMVD prevalence in the agro-ecosystem.


MSc. Thesis


rice production, Rice yellow mottle virus, Chrysomelid beetles, grasshoppers, insect vectors, Kilombero, Tanzania