1. New methods were designed for the simultaneous determination of the unidirectional flow of air and the total abdominal pumping in flying locusts, for measurements of the potential and the actual rate of flow caused by thoracic pumping, and for an independent estimate of the total ventilation of the flight system.
2. During rest, flight and recovery in the desert locust, the unidirectional flow caused by abdominal pumping remains small and almost constant at 30 l. air/kg./hr., in through the thoracic spiracles and out through the abdominal ones. The total pumping amounts to about 180 l./kg./hr. in flight of which 70 l. ventilate the thorax and 80 l. the other paits of the body.
3. Abdominal pumping can be blocked reversibly or reduced to insignificance without impairing the wing movements of the desert locust.
4. During average horizontal flight of the desert locust, the thoracic ventilation is about 320 l. air/kg./hr. of which 250 l. are moved by the thoracic pump, but the capacity of this pump is 760 l./kg./hr. and can be increased to at least 950 l./kg./hr. The relatively low efficiency is likely to increase when the abdominal air sacs are deflated due to ingested food, fat or eggs, i.e. when the animal has to lift more.
5. The pressure changes caused by the thoracic pumping only amount to 10-25 mm. H2O and are of no mechanical significance for the moving wings.
6. Draught ventilation due to a Bernoulli effect is of no significance in locusts and probably not in dragonflies and wasps.
7. The oxygen in the thorax of flying locusts is reduced by about 5.5 % relative to the atmosphere at sea level.
8. At small to medium relative humidities, and at temperatures between 25 and 30° C. at sea level, the rate of ventilation permits sustained flight of the desert locust without risk of desiccation (Fig. 14). In order to retain a positive water balance at higher air temperatures the locusts must fly at high altitude, and 3 km. is estimated as a maximum for sustained, active flight.
9. Large dragonflies (Aeshna spp.) depend almost exclusively on thoracic pumping during flight, while large wasps (Vespa crabro) depend on abdominal pumping. For both types the metabolic rate is about 100 kcal./kg./hr. during level flight.