Effect of using different types of animal dung for feeding and nesting by the dung beetle Onthophagus lecontei (Coleoptera: Scarabaeinae)

Onthophagus lecontei Harold, 1871 is an American dung beetle that feeds on the dungs of a variety of species, perhaps owing to hitherto unknown differences in their effect on its development and survival. We tested whether using different types of dung (exotic and native) for feeding and nesting affects O. lecontei’s progeny. Adult beetles from the field were randomly paired and assigned to horse (Equus ferus Boddaert, 1785), goat (Capra hircus aegagrus Erxleben, 1777; domestic), or wild rabbit (Sylvilagus cunicularius (Waterhouse, 1848); native, endemic) dung under laboratory conditions. The number, mass, and volume of their brood masses, the number of emerged beetles, adult size, and duration of preimaginal stages (egg, larva, and pupa) were evaluated. There were differences for all variables: O. lecontei reared in wild rabbit dung produced more progeny, more brood masses, and larger adult beetles, and offspring remained in each preimaginal stage for a shorter period of time. Onthophagus lecontei is able to feed and nest using all three types of dung, but wild rabbit dung is the most favorable for its development. This suggests the existence of a long-standing association between O. lecontei and this native rabbit and the optional relationships with introduced herbivores; plasticity in reproductive behavior that may be useful when the optimal resource is not available.

Field observations on competitive displacement, at the preimaginal stage, of Culex quinquefasciatus Say by Culex cinereus Theobald (Diptera: Culicidae) at the Kenya Coast

In certain areas of the Kenya coast, Culex quinquefasciatus Say is unable to maintain itself in breeding sites (flooded pit latrines) which it has to share with C. cinereus Theo. The pattern of settlement of the two species and the replacement of C. quinquefasciatus by C. cinereus were studied from May to November 1980 by monitoring newly emerged males as they departed from two breeding sites located in a small village near Mombasa. C. quinquefasciatus was the first species to be recorded from both sites, soon after they were flooded by the early rains. C. cinereus came later and did not increase markedly until after the late rains. The pattern of replacement of C. quinquefasciatus by C. cinereus was similar in the two breeding sites; the former species was unable to maintain itself once C. cinereus started to increase. Studies in another village showed that, after displacement, egg laying by C. quinquefasciatus continued but at a much reduced level. It is suggested that this is an example of competition-mediated succession occurring annually, with C. quinquefasciatus being better adapted to exploit rapidly the newly flooded sites but unable to sustain later competition from C. cinereus.