THERMAL DISINFESTATION STUDIES ON HESSIAN FLY AND WHEAT MIDGE
Venkatesan, V. S.
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Thermal disinfestation strategy is gaining importance as an alternate to method of insect control in stored grain, but minimal information exists the use of thermal disinfestation for alfalfa and other hay products. At present, phytosanitary requirements on the export of heat treated alfalfa and the need to declare the product free of Hessian fly necessitate the use of 90 C product temperature. Reduction in this temperature requirement calls for actual determination of the thermal kill point of the Hessian fly. In the current study, the thermal kill point of wheat midge and Hessian fly were determined and found to be in the range 52.5 C to 55 C for an exposure time of 3 minutes. A time-temperature study on the thermal ill resulted in a series of sigmoidal dose response curves. The thermal kill data to were incorporated in simulation models for two types of dryers. The simulation results show that disinfestation can be obtained at lower temperatures, and even products with lower input moisture content (30%) could be disinfested. Prior to this study, only alfalfa with a moisture content of 55% and above could be used in the dryer. Experimental determination of the thermal kill point and consequent lowering of the temperature requirement results in a better product and optimises the energy requirements. A simulation traces the viability of the insect as it passes through a dryer with the product.