Interactive Effects of Low-oxygen Atmospheres, Relative Humidity, and Temperature on Mortality of Two Stored-product Moths (Lepidoptera: Pyralidae)

Interaction of oxygen concentration, temperature, and relative humidity with time required to kill Indianmeal moth, Plodia interpunctella (Hübner) and navel orangeworm, Amyelois transitella (Walker), was examined. Late larval and early pupal stages of navel orangeworm and pupae of Indianmeal moth were exposed to combinations of 0.5, 1, 2, or 5% O2. (with 10% CO2 and a balance of N2) at 15.6, 21.1, or 26.7°C and at 40 or 60% RH. These gas concentrations simulate the output atmosphere of a low-O2 generator fueled with methane or propane. Lethal time to kill 95% (LT95) of the population of each insect was determined by regression analysis for each combination of factors. A general equation was developed through multiple regression analysis of the LT95's for each insect species to describe the relationships. Temperature effects were similar for each species and could be made linear with a reciprocal transformation of the LT95 plotted against time. Effects of relative humidity and atmosphere on the LT95 were different for the two species. Indianmeal moths were affected more by changes in O2 concentration while navel orangeworms responded more to changes in relative humidity. Further analyses led to estimates of the low temperature threshold (i.e., temperature below which atmospheres would be ineffective) and to estimates of a constant, k, describing the time/temperature relationship. The time/temperature curve is described by a hyperbola and exposure time can be estimated accordingly.