Predicting mortality of phosphine‐resistant adults of Sitophilus oryzae (L) (Coleoptera: Curculionidae) in relation to changing phosphine concentration

Abstract

Adults of a phosphine-resistant strain of Sitophilus oryzae (L) were exposed to constant phosphine concentrations of 0.0035-0.9mg litre(-1) for periods of between 20 and 168h at 25 degrees C, and the effects of time and concentration on mortality were quantified. Adults were also exposed to a series of treatments lasting 48, 72 or 168 h at 25 degrees C, during which the concentration of phosphine was varied. The aim of this study was to determine whether equations from experiments using constant concentrations could be used to predict the efficacy of changing phosphine concentrations against adults of S oryzae. A probit plane without interaction, in which the logarithms of time (t) and concentration (C) were variables, described the effects of concentration and time on mortality in experiments with constant concentrations. A derived equation of the form C(n)t = k gave excellent predictions of toxicity when applied to data from changing concentration experiments. The results suggest that for resistant S oryzae adults there is nothing inherently different between constant and changing concentration regimes, and that data collected from fixed concentrations can be used to develop equations for predicting mortality in fumigations in which phosphine concentration changes. This approach could simplify the prediction of efficacy of typical fumigations in which concentrations tend to rise and then fall over a period of days.

Rapid genome wide mapping of phosphine resistance loci by a simple regional averaging analysis in the red flour beetle, Tribolium castaneum

“…It has been in use for nearly five decades owing to its broad spectrum of activity and residue-free characteristics [3,4]. Heavy reliance on phosphine has given rise to high-level heritable resistance in several grain insect pests, threatening the efficacy of phosphine [5-10]. …”

Numerical Simulation of Gas Flow through a Cylindrical Grain Storage

“…However, the fumigation process sometimes is reported to fail [5,6]. Efforts to identify the causes of fumigation failure and the development of strategies for effective phosphine use amid the threat of insect resistance have started to take place [7][8][9][10][11]. Central to these efforts is the need for a good understanding of how the phosphine gas behaves in grain storage and the factors that influence the distribution of the gas.…”