Computer modelling of insect-induced hot spots in stored grain

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Mani, Seshadri
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A computer model of the development of insect-induced hot spots in stored grain was developed by combining four submodels: (1) a three-dimensional, finite element model of heat transfer, (2) a population dynamics model of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), (3) a model of heat production of C. ferrugineus, and (4) a model of movement of C. ferrugineus. The higher the initial insect density and the initial grain temperature, the higher and the earlier was the possibility for hot spot occurrences. In large diameter bins, hot spots occurred at the end of fall and the centre temperatures reached a peak of 40$\sp{\circ}$C. Insects initially introduced in the north side moved to the centre and caused hot spots earlier than when the insects were initially introduced in the south side of the bulk. In a validation experiment, no hot spot was developed in two bins of 1-m diameter filled with wheat of an initial grain temperature of 28$\sp{\circ}$C and an initial moisture content of 13.2% to adepth of 1-m and located in a laboratory; 10,000 adults were initially introduced at the centre of the grain bulk. For the experimental conditions, the hot spot model predicted no possibility for hot spot development. The hot spot model includes the feedback from the insect model to the temperature model. The hot spot model predicted a maximum insect population of 120 adults/kg and temperature of 39$\sp{\circ}$C in a hot spot developed at the centre of a 8.5-m diameter wheat bulk with an initial grain temperature of 30$\sp{\circ}$C and 10,000 adults introduced at the centre of the bulk. For the same simulation conditions, the spatial model predicted a maximum of 500 adults/kg and predicted no increase in the temperatures. (Abstract shortened by UMI.)