Social determinants of aggregation behaviour in adults of the desert locust

The social aggregation behaviour of adults of the desert locust Schistocerca gregaria, was found to be determined by rearing density, in the same way but not to the same extent as that of nymphs. Adult locusts reared crowded since hatching showed more social grouping than adults reared in isolation. For adults, the least amount of grouping was shown by isolates, F₁ of solitaria caught in the field. Both nymphs and adults were found to be attracted to the edge of the testing arena in inverse proportion to their attraction to each other. This edge effect could be used as one behavioural measure of phase polymorphism complimentary to the measure of social aggregation. Unlike nymphs, adults did not rapidly learn to group when forced into contact with one another. Grouping of isolated adults was not found to change with age.