Zonal recovery and orientation in respect to various stimuli of Heterocerus fenestratus Thunberg, 1784 (Coleoptera, Heteroceridae)

The orientation of heterocerid beetles, Heterocerus fenestratus Thunberg, from marsh and river banks was tested in the field by releasing specimens after removal from water and placing on a dry compact substratum. On the latter both populations showed a zonal recovery capability probably by means of visual cues. In water the river beetles showed a zonal recovery capability while those from the marsh oriented at random. In respect to various visual stimuli, laboratory exeriments showed: (1) positive phototaxis to the sun in the marsh population; (2) absence of sun orientation in the river population; (3) choice of the brighter part of the horizon in both populations and (4) positive phototaxis towards artificial monochromatic lights. This latter reaction increased with decreasing wavelengths in both populations. The river beetles were more sensitive to the violet light (403 nm) and did not respond to red (749 nm), while the marsh beetles were more sensitive to U.V. (342 nm) and responded to red (749 nm). The behavioural differences between the two populations are discussed according to their different habitats.