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) o f Callosobruchus subinnotatus (Pic.) were investigated for their tolerance or susceptibility to four modified atmospheres. Two of these atmospheres we re hypercarbic and two were hypoxic. The hypercarbic atmospheres were found to cause mortality earlier than hypoxic atmospheres. Late pharate adults d ied earlier than pupae or early pharate adults. Late pharate adults that su rvived the exposure took a longer time to eclose than the pupae or early ph arate adult. Using high resolution microrespirometric techniques, it was possible to rec ord the oxygen consumption rate and CO2 output of different developmental s tages in air. The metabolic rate was determined manometrically as the oxyge n uptake rate at an ambient temperature of 25 degrees C. The oxygen uptake rate differed significantly between groups of 20 individuals of different s tages (p < 0.01; t-test). The lowest rate of oxygen uptake (510.6+/-52.2 mu l g(-1) h(-1)) was recorded in pupae. Higher oxygen uptake rates were foun d in early pharate adults (668.4+/-45.6 mu l g(-1) h(-1)) and late pharate adults (1171.2+/-45.0 mu l g(-1) h(-1)), and adult beetles (1310.4+/-53.4 m u l g(-1) h(-1)). The patterns of CO2 release were similar to those of oxyg en uptake. CO2 release was highest in eclosed adults and late pharate adult s followed by early pharate adults, and lowest in pupae. The mode of CO2 re lease ranged from continuous CO2 release in pupae to discontinuous CO2 rele ase in late pharate and eclosed adults. Thus, high metabolic rates, and per haps, in conjunction with discontinuous CO2 of late pharate adults are resp onsible for their higher susceptibility to modified atmospheres than pupae and early pharate adults. (C) 2000 Elsevier Science Ltd. All rights reserve d.