Individual and combined efficacy of zeolite and spinetoram for controlling Rhyzopertha dominica (F.) (Bostrichidae: Coleoptera); impact of temperature, relative humidity and grain types

Laboratory experiments were conducted to investigate the insecticidal potential of zeolite (ZeoFeed) and spinetoram alone and in combination against the adults of lesser grain borer, Rhyzopertha dominica (F.) (Bostrichidae: Coleoptera). Bioassays were carried out at 15, 25, and 35 °C and 55 and 75 % relative humidity (R.H.) on wheat, rice, and maize. Efficacy of zeolite was determined at 2500, 500, and 700 ppm in first bioassay, followed by efficacy of spinetoram at 0.25, 0.50 and 1 ppm in second bioassay, and combined effectiveness of zeolite and spinetoram at 750 and 1 ppm doses in third bioassay. Adult mortality in all bioassays was recorded 1-, 3-, 7- and 14-days post-exposure. Results showed that mortality was positively related with dose and exposure interval. More insects died with increasing temperature and decreasing R.H. Wheat was more susceptible followed by rice and maize. Mortality was more in combined treatments (750 ppm + 1 ppm) with complete control of insects at 35 °C + 55 % R.H., 14 days of post-exposure in all tested commodities. This is the first report on the use of zeolite combined with insecticide to combat R. dominica under these conditions. The study suggests that zeolite in combination with spinetoram can effectively protect grains from this species, considering factors such as temperature and relative humidity.