Botanical oils and controlled atmospheres (CAs) are natural, safe and eco-friendly alternatives of chemical fumigants for management of insect pests infesting stored grain. Oil effects of geranium, coriander and cumin were investigated on the bioactivity of CAs of three elevated CO2 concentrations (25, 50 and 75% in the air) on S. oryzae adults at 20 and 30°C. Bioassay tests were conducted for botanical oil and CO2 each alone and as a binary combination. Experiments of CAs were performed using a re-circulatory multi-flask apparatus. Results indicated that the required times to kill 50 or 90% (lethal times, LT50 and LT90) of S. oryzae adults reduced significantly by the combination of tested oil and CO2. The lethal times (LT90s) were significantly the longest, when each of 25% CO2, geranium, coriander and cumin (each oil was at 1.5% v/w on wheat grains) were tested separately, at 20°C. These times were 12.09, 7.83, 5.82 and 8.09 days in treatments of 25% CO2, geranium, coriander and cumin, respectively. These times significantly reduced to 6.14, 4.15 and 4.15 days, when each of geranium, coriander and cumin oils were separately combined with 25% CO2, respectively. Furthermore, coriander oil was the most effective at 30°C on the lethal time of CA of 75% CO2. It caused a reduction in LT50 and LT90 of CA of 75% CO2 from 1.12 and 4.1 days to the shortest lethal times 0.65 and 1.66 days for the adults of S. oryzae, respectively. It was concluded that efficacy of CO2 can be significantly increased by using it with botanical oils in insect control and this action becomes the greatest at the highest CO2 concentration and higher temperature than lower one. |
