[Studies in the ethology, antecology and ecophysiology ofElaphrus cupreus Dft. andElaphrus riparius L. (Coleoptera, carabidae) : On the living conditions and behaviour of the visually hunting carnivorous type of groundbeetles].

The study of two species of stenotopic riparian carabides exemplifies the living conditions and behaviour of the visually hunting carnivorous ground-beetles. 1. E. riparius lives in barren riparian regions exposed to the sun, whereasE. cupreus is found on shady banks covered with vegetation. As far as preying is concerned, the behaviour of these two species does not differ from that of other visually hunting insects. Territorial behaviour can sometimes be observed when they defend a den; it occurs regularly when they defend prey. They react to aggression either by resorting to action or by becoming motionless. In the first case, escape behaviour can be observed, whereas in the latter case they resort to a state of akinesia on bieng touched. When severely menaced, they tend to stridulate and to empty their pygidial glands. InE. cupreus, flying capacity serves for the extention of the habitat only, whereas withE. riparius it is a means of escape (flying speed in the latter: 5.9 km/h=3.7 mph). Copulation behaviour consists of a chain of activities, the three links of which-approach, prehension, and copulation-are released by visual, olfactory, and tactile stimuli. The olfactory stimulus they peceive before mounting implies the interspecific copulation barrier. The oviposition behaviour is adapted to the specific biotopic conditions. On average, the development from egg to imago takes 28.3 days inE. riparius, 37.5 days inE. cupreus; it takes place in summer. The maturation of the imagines occurs without obligatory dormancy within one to two months. Thus, the species ofElaphrus represent an original type of annual rhythmicity. In order to hibernate, the beetles bury themselves about 5 cm below the surface of the ground. Their life span amounts to app. 12 months, one hibernation included. 2. The imagines of both species are active by day. The diurnal pattern of activity is closely related to changes in illumination and temperature. The males are more active. The nocturnal activities of the larvae are thought to represent an isolating mechanisms against the imagines. 3. Surface, number of ommatidia and the anatomy of the compound eyes show that the eyes ofE. riparius are less sensitive to light than those ofE. cupreus. This is accompanied by changes of the inner proportions of the eyes in the usual manner. The acuteness of vision of the two species is similar; the field of vision ofE. riparius extends horizontally, that ofE. cupreus dorsally. Individual parts of the eye display a specialization typical of visually hunting insects. During the optomotoric experiment,E. cupreus achieves its optimal acuteness of vision at a lower light intensity thanE. riparius. 4. In light and infrared gradientsE. riparius prefers higher intensities thanE. cupreus. 5. The beetles enlarge hiding-places on the ground by some instinctive activity. Radiation and descent of moisture in the air enhance the appetence for the fixed pattern by raising body temperature and increasing transpiration. Thus the fixed pattern must be considered to be a mechanism which regulates the behaviour of the animals by radiation.