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A study of the heating of stored grain caused by insects
Author(s) -
HOWE R.W.
Publication year - 1962
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1962.tb05995.x
Subject(s) - thermal conduction , convection , biology , population , population density , materials science , mechanics , composite material , physics , demography , sociology
SUMMARY The rates of increase of temperature and of population density are calculated for an insulated culture of granary weevils, assuming a Malthusian rate of increase, and basing heat production on respiration rates. This is done first by a step method, but it is shown that the increase in population density can be related to rise in temperature, irrespective of the original density, which makes a short‐cut method possible. The calculations are then modified for the situation in which the culture is embedded in and loses heat by conduction to a bulk of uninfested grain. The spread of heat by conduction is slow; spread by convection is not considered. At I m. from a hot pocket with a steady heat output, the rise of temperature at equilibrium will be less than half the rise at the margin of the hot pocket and only 15% of this rise will be achieved in 4 weeks. The numbers of insects needed to raise the temperature of an infested pocket in a grain bulk are much larger than those required for an insulated culture. The extra time required to reach a temperature is that needed to build up a sufficient population in the original environmental conditions. It is argued that hot pockets increase in size because of the movement of insects induced by high temperatures and by overcrowding, rather than because of spread of heat by conduction. Convection currents cause upward, but not lateral, extension of hot pockets. If sufficient insects are to develop to produce enough heat to cause high temperatures the expansion of a hot spot is necessary, so that small cages of insects cannot be used to induce heating experimentally. Warehouse observations are described to support these predictions. Heating of home‐produced grain in Britain is caused chiefly through storing either grain which is damp and therefore heats, or dried grain which has been insufficiently cooled. Either produces an ideal environment for any stored‐grain insect species. Stored grain should be inspected both to find insects and to measure its temperature and moisture content. Any warehouse containing grain at temperatures above 22° C. and insects should be examined monthly.