|Year of Publication:
|W. W. Keith Houston, McIntyre P.
|Entomol. exp. appl.
|COLEOPTERA, crepuscular flight, dung beetle, Onitis alexis, Scarabaeinae, superposition eyes
The role of light intensity and temperature in determining the onset of flight in the crepuscular dung beetle Onitis alexis Klug (Coleoptera: Scarabaeidae) was examined. Flight under natural light was highly syn- chronized, with two-thirds of the beetles that flew flying over a period of 10-12 min. In six flights on differ- ent days, the mean time of onset varied by up to 13 min, but mean onset occurred at fixed light intensity. Absolute light intensity therefore appears to be a vital cue in determining flight onset. Mean onset remained at this intensity when dusk was advanced artificially by up to about 8 min. However, when dusk was brought further forward, mean flight occurred at lower intensities and onset of flight took place over a longer period. This is interpreted as an overlapping of the period of light intensities suitable for flight with the circadian rhythm that brings the beetles to the surface. No beetles flew when kept under constant bright light or in the dark during the dusk period. Under conditions of constant dusk, the beetles appeared uncoordinated and, although the median time of onset of flight was only 3 min later than in the control flight, onset of flight was spread out over a much longer period. At soil temperatures of 20-22 ~ over 90% of the beetles flew. This percentage decreased with decreasing temperature, and less than 10% flew at temperatures of 16-17 Celcius.