The Reproductive Behaviour and the Nature of Sexual Selection in Scatophaga stercoraria L. (Diptera: Scatophagidae): I. Diurnal and Seasonal Changes in Population Density Around the Site of Mating and Oviposition

Abstract

calypterates as being closely related to the Muscidae. The family includes species of very varied habits; Scatophaga stereoraria L. ( = Scopeuma stercorarium) is the common yellow dung fly found around droppings throughout the northern hemisphere and occurring as far south as North and South Africa and the Canary Islands. Despite its ubiquity, Scatophaga stercoraria has attracted only cursory investigation with the exception of the works of Cotterell (1920) and Hammer (1941). From Hammer's excellent monograph, the reproductive biology of the species may be summarized as follows. The males arrive first around the fresh droppings, often in considerable numbers. As the females arrive, they are immediately grasped by the nearest male. After copulation, the male remains mounted above the female during oviposition, though he retains contact with the female only by means of the grasp of his front tarsi around the junction between her thorax and abdomen. At this time the genitalia are quite free and the middle and hind legs of the male rest on the surface of the dung. During the time that the male is paired to the female, fierce struggles may arise should second males attempt to gain possession of the female. The eggs are laid in a single dropping and the larvae hatch out on to the dung surface, into which they burrow immediately. Pupation takes place either in the crust of the dropping or in the soil beneath, and the adults emerge some 3-4 weeks after oviposition. The females emerge about a day before the males (Lewis & Bletchly