in locust flight muscle, trehalase is bound to membranes that appear in the microsomal fraction upon cell fractionation, but the exact cellular location is not known. The trehalse reaction is irreversible under physiological conditions, thus the the enzyme would hydrolyse all available trehalose. In resting locusts, trehalase in flight muscle shows low activity, although the concentration of its substrate in the haemolymph is very high. with the onset of flight, when ATP turnover in flight muscle increase dramatically, trehalose utilization rises by more than 10-fold, and this requires a corresponding increase in trehalase activity. Hence, the activity of trehalase in locust flight muscle must be regulated, but the mechanism of control has remained obscure despite several attempts to understand this problem. Insect trehalase activity has not been found to be modulated by hormones, second messengers, allosteric effectors or reversible interconversions. It has, however, been shown that trehalase in homogenates of locust flight muscle appears in two forms, an overt form that is active without further treatment and a latent form that is inactive but can be activated in vitro by detergents or other means that destroy the structural integrity of membranes. Also, Candy (1974) observed an increase in the overt form but no changes in the total activity of flight muscle trehalase after short flight. The mechanism of this phenomenon has remained obscure.