Tolerance of pupae and pharate adults of Callosobruchus subinnotatus Pic (Coleoptera: Bruchidae) to modified atmospheres: a function of metabolic rate

Three developmental stages (pupae, early pharate and late pharate adults) of Callosobruchus subinnotatus (Pic.) were investigated for their tolerance or susceptibility to four modified atmospheres. Two of these atmospheres were hypercarbic and two were hypoxic. The hypercarbic atmospheres were found to cause mortality earlier than hypoxic atmospheres. Late pharate adults died earlier than pupae or early pharate adults. Late pharate adults that survived the exposure took a longer time to eclose than the pupae or early pharate adult. high resolution microrespirometric techniques, it was possible to record the oxygen consumption rate and CO2 output of different developmental stages in air. The metabolic rate was determined manometrically as the oxygen uptake rate at an ambient temperature of 25°C. The oxygen uptake rate differed significantly between groups of 20 individuals of different stages (p<0.01; t-test). The lowest rate of oxygen uptake (510.6±52.2 μl g−1 h−1) was recorded in pupae. Higher oxygen uptake rates were found in early pharate adults (668.4±45.6 μl g−1 h−1) and late pharate adults (1171.2±45.0 μl g−1 h−1), and adult beetles (1310.4±53.4 μl g−1 h−1). The patterns of CO2 release were similar to those of oxygen uptake. CO2 release was highest in eclosed adults and late pharate adults followed by early pharate adults, and lowest in pupae. The mode of CO2 release ranged from continuous CO2 release in pupae to discontinuous CO2 release in late pharate and eclosed adults. Thus, high metabolic rates, and perhaps, in conjunction with discontinuous CO2 of late pharate adults are responsible for their higher susceptibility to modified atmospheres than pupae and early pharate adults.