Effects of dung fauna on survival and size of buffalo flies (Haematobia spp.) breeding in the field in South Africa and Australia.
Abstract
The effects of dung arthropod fauna on the survival and size of Haematobia thirouxi potans in South Africa and the introduced H. irritans exigua in Australia were examined in the field to assess prospects for improving biological control of the latter. Female flies were induced to oviposit on prepared dung pads, which were then placed in the field, either on a platform 2 m high where they were not colonized by dung arthropods (control pads), or on the ground where they were accessible to these fauna (fauna pads). The difference in egg to adult survival between control pads and fauna pads, expressed as a percentage of survival in control pads, gave an estimate of the fauna-induced mortality. Dung pads were exposed on 8 occasions at each of 4 localities: (1) in grassveld on sandy loam at Boekenhoutskloof near Pretoria, Transvaal; (2) and (3) in grassveld and bushveld, respectively, on a clay loam in Hluhluwe Game Reserve, Natal; and (4) in grassveld on a clay loam at Rockhampton, Queensland. The abundance of dung beetles and the amount of dung dispersal (removal and shredding of pad remains) were assessed at each exposure. On most occasions in all localities, the dung fauna caused considerable mortality of immature Haematobia and stunting of adults. In the Transvaal, where dung removal by dung beetles was substantial and rapid, the mean fauna-induced mortality was 97.6%. In Natal, fauna-induced mortality was lower (92.8% in grassveld and 84.3% in bushveld) and much of this mortality could be attributed to the activity of predators or parasitoids. In Queensland, fauna-induced mortality (66.7%) was significantly lower and more variable than in Africa. The African dung fauna, therefore, may contain species of dung beetles (Scarabaeinae), predators or parasitoids that, if introduced into Australia, would increase and help to stabilize the level of fauna-induced mortality in the immature stages of H. irritans exigua.