Effect of an Indigenous Nigeria Rice Variety on Tolerance of Sitophilus oryzae Strains to Insecticide

The impact of a common indigenous Nigerian rice variety on insecticide tolerance of local and foreign strains of Sitophilus oryzae was investigated. Three strains of S. oryzae (Morocco, Trinidad and Nigeria strains) were reared separately on two cereals, rice (Ofada variety, a local Nigerian variety native to the Southwestern part) and wheat (Hard Red Winter variety). The susceptibility of the resulting six populations of S. oryzae to DDVP was tested at 28±2 °C and 70±5% relative humidity. Adult weevils from each population were exposed to DDVP impregnated filter papers (with concentrations ranging between 1.0 x 10^-5 % to 1.0 x 10^-2 %). Insecticide tolerance of S. oryzae to DDVP was greatly influenced by the concentration of insecticide, exposure time and food type. The Nigerian strain (on Ofada) population were the most susceptible while Trinidad strain (on Ofada) population were the most tolerant. The busiest seaports in Nigeria are located in the Southwestern part of the country, hence, the study reveals the need to guard against the entrance of exotic strains of S. oryzae through the importation of wheat or rice.