AbstractDung-colonising beetles, commonly known as dung beetles, provide several ecosystem services for farmland pasture systems. However, dung beetles are in decline in northern temperate regions, in part due to widespread endectocide use for control of pests and parasites of cattle. Endectocide residues are excreted in the dung of cattle, at concentrations that are still toxic to insects.
The overall aim of this study was to examine the effects of endectocide exposure on the reproductive output of dung-colonising beetles. To achieve this, the first objective was an examination of the short-term sublethal effects of ivermectin, a macrocyclic lactone, on two common northern temperate species, Onthophagus similis (Scriba) and Aphodius prodromus (Brahm). Constant exposure of field-collected adult beetles, over a period of 3 weeks, resulted in smaller oocytes of O. similis at 1 ppm (wet weight). Beetles also had smaller fat bodies and motility was reduced. The study of A. prodromus was inconclusive due to extensive mortality in all treatments.
The second objective was an examination of different long-term endectocide treatment regimes (macrocyclic lactones, synthetic pyrethroids, or no treatment) on 24 beef cattle farms, using pitfall trapped beetle samples. Four species of dung beetle were considered: Aphodius rufipes (L.), Aphodius fossor (L.), Onthophagus coenobita (Herbst) and O. similis. Endectocide use was associated with a lower proportion of gravid O. similis females. A more variable size of O. similis and a smaller size of A. fossor was seen on farms using macrocyclic lactones. On the other hand, A. rufipes was larger on farms using endectocides, possibly through reduced competition with other species. The reproduction of A. fossor or O. coenobita did not appear to differ between regimes.
The study suggests that beetle reproductive output is affected by endectocide use and in the long-term, such effects may be as ecologically damaging as lethal effects.
|Date of Award||6 Nov 2018|
|Supervisor||Richard Wall (Supervisor)|