Effect of Insecticide Application Rates on Population Density of Orseolia oryzivora in Relation to its Parasitoids on Rice

Abstract

Africa rice gall midge (Orseolia oryzivora) is a major insect pest of rice and the use of insecticides in its control poses danger to the environment and destroys biodiversity. The experiment was conducted to evaluate effect of lambda-cyhalothrin and carbofuran rates on population density of O. oryzivora in relation to its parasitoids on rice. The treatments were arranged in split-plot and fitted in to Randomized Complete Block Design, replicated three times. Observations were made on tiller number per hill, plant height, days to 50% flowering, % incidence, % severity, % parasitism of O. oryzivora, panicle /m2, grains / panicle and yield of rice. Data collected were subjected to Analysis of Variance and significant means were separated using Least Significant Difference (LSD) at p<0.05. The result showed that Rice plants treated with lambda-cyhalothrin at rate of 1L/ha, 0.75 L/ha, Carbofuran at rate of 10.0 kg/ha and 7.5 kg/ha had higher yield (2.90-2.97 tonnes/ha) compared with control (2.55 tonnes/ha). They also had lowest incidence (2.09-2.64%) and severity (2.40-3.72%) of O. oryzivora compared with 8.26-17.17% and 9.93- 14.72% in plants treated with lambda-cyhalothrin at 0.50 L/ha and control respectively. The parasitism of O. oryzivora was high on rice plants treated with Carbofuran and the untreated ones (1.16-1.74) compared with other application of lambda-cyhalothrin.