Microcalorimetric and mass spectrometric methods for determining the effects of controlled atmospheres on insect metabolism

Metabolic heat rates of small insects which fit in 1 cm3 ampoules can be measured readily using the Calorimetry Sciences Corporation 4100 DSC in the isothermal mode. The rapid thermal equilibration of the calorimeter on changing to a new isothermal temperature also permits the response of the metabolism to change in temperature to be determined quickly. By modifying the ampoules and measuring chamber lid for entry of silica capillaries to allow the headspace in the ampoules to be changed in situ, direct comparison can be made of metabolic heat rates in air and in controlled atmospheres. These results aid in assessing the effectiveness of controlled atmospheres, such as low oxygen and/or high carbon dioxide, as potential replacements of methyl bromide for fumigation of fresh produce. For a range of insects tested, including larval, pupal and adult stages, metabolic heat rates decrease to very close to zero under anoxic conditions. By analysis of the headspace of an ampoule containing an insect using ms, changes in metabolic heat rate can be related directly to compositional changes in the headspace, including those resulting from the insect’s metabolism. Important factors in the application of mass spectrometry to the more difficult task of measuring rates of oxygen consumption and carbon dioxide production associated with a metabolic heat rate are discussed.