Monitoring Fumigation Effectiveness Using Bioassays of Mixed Aged Cultures of Target Pests

Mixed age cultures of several target insect species of typical resistance levels, were accommodated in specially constructed containers (vials) and placed in the commodity at the top of the storage immediately prior to fumigation. The storage was then fumigated as per normal procedures. Insect vials were removed from the fumigation area periodically during the fumigation process. The cultures were then assessed for survivors. The results were collated with concentrations and time at that concentration and compared against laboratory data. Minimum Ct products were calculated for complete control of adults and immature stages for each time period under fumigation. Results indicated that some of the label rates specified, more precisely those pertaining to low flow fumigation, were inadequate. These were subsequently raised from 35 ppm for 14 days to 100 ppm for 14 days. Bioassays were also used to compare the effectiveness of various control methods. The success of these trials has highlighted the value of mixed age cultures to assessment of pest control strategies against target