RESPIRATORY PHYSIOLOGY OF LARVA OF DONACIA SIMPLEX, A ROOT-PIERCING BEETLE

The root-piercing spiracles of the larva of Donacia simplex provide an uninterrupted pathway for oxygen between the gas spaces of the root and the tracheal system. The insects rely upon the plant for oxygen. The mud surrounding the larvae and roots is anoxic. When oxygen is absent or its partial pressure low an oxygen debt is built up and lactic acid accumulates. The lactic acid levels of the larvae on the plants are the same as those of larvae respiring in air. The amount of energy produced from the formation of lactic acid is onehundredth of the calculated ATP production in air. The oxygen uptake of the larvae occurs by diffusion and does not hinder the metabolism of the plant. During winter the ambient oxygen partial pressure may fall to 1 per cent if the plants are covered with water. Adaptations for survival at low oxygen pressures show a seasonal variation. Throughout the year starvation reduces metabolism by a half; between 4 and 14°C the QO2 is doubled. During the summer small amounts of lactic acid accumulate when the oxygen pressure is low, but during the winter no lactic acid accumulates under such conditions and the metabolism is depressed, an effect distinct from those caused by starvation or by changes in temperature. © 1969.