1. Hoppers of the locust Locusta migratoria migratorioides R. & F., which have been reared crowded, exhibit characteristic marching behaviour in the laboratory in foodless cages under standard conditions.
2. The rate of attainment of maximum marching by a given group of hoppers is greatest following a short period of starvation immediately preceding transfer to these conditions.
3. A meal of filter-paper soaked in sugar solution only, exerts no retarding effect on the rate of attainment of full marching, whilst if an adequate concentration of potassium salt is added in addition a definite retardation is observed.
4. In locusts actively feeding on grass the potassium content of the blood is relatively high, and it is suggested that this causes a reduced muscular efficiency which may explain retardation in attainment of full marching.
5. The marching pattern is the result of the activity of particular nerve centres which require a period of activation by a combination of factors before full expression is achieved. Two final factors are essential for the maintenance of the marching state, a low concentration of blood potassium and mutual stimulation by other marching hoppers.
Biochemistry of locusts. 4. Insectorubin metabolism in the desert locust (Schistocera gregaria Forsk.) and the African migratory locust (Locusta migratoria migratorioides R. & F.)