Effects of DDT on oxygen consumption of Rhodnius prolixus Stål

Abstract

When fasting fifth-instar larvae of Rhodnius prolixus Stål were poisoned with a lethal dose of DDT, the rate of oxygen consumption increased from the onset of hyperactivity, reached a marked peak shortly after knockdown, and then declined. For some days after the peak the oxygen consumption was markedly in excess of that prior to poisoning with DDT. Eventually, the oxygen consumption fell below the pre-teatment value and continued at this low level for some days, although the insect was then undoubtedly dead and in one case had been bisected. There was no marked discontinuity in the declining phase of oxygen consumption and therefore there is no indication of when death occurred. It is concluded that the time of death in DDT-poisoned larvae of Rhodnius cannot be determined by measurements of oxygen consumption.The total oxygen consumed from poisoning until death was always less than that consumed in the normal use of all metabolic reserves by the fasting insect, and these experiments do not support the hypothesis that death in DDT poisoning is due to total exhaustion of metabolic reserves. However, it is pointed out that, in Rhodnius, some of the metabolic reserves are contained in the undigested residue of the blood-meal and in the massive endocuticle and that there is no reason to think that either digestion of the remaining blood-meal or resorption of the endocuticle could be speeded up during DDT poisoning. Hence there is a strong possibility that, in DDT-killed Rhodnius, death is brought about by exhaustion of the available reserves.The peak rate of oxygen consumption during poisoning was greatest in very recently fed larvae and decreased as the interval between moulting and DDT-treatment was increased. This suggests that knockdown occurs when the fuel demands of the DDT-induced activity exceed the rate at which the fuel can be mobilised from the metabolic reserves.