Population status of the bush fly, Musca vetustissima (Diptera: Muscidae), and native dung beetles (Coleoptera: Scarabaeinae) in south-eastern Australia in relation to establishment of exotic dung beetles

Abstract

AbstractWe compare the pest status and age structure of bush fly,Musca vetustissima Walker, populations, and the abundance of native dung beetles at Uriarra, ACT, for five fly seasons before (1976–81) and three seasons after (1990–93) the exotic dung beetles Euoniticellus fulvus (Goeze) and Onthophagus taurus (Schreber) became established in the area during the late 1980s. Fly populations in all post-introduction seasons of 1990–93 were much older than in the pre-introduction seasons, indicating reduced levels of local fly breeding and higher proportions of immigrants. During the pre-introduction period, the fly annoyance index exceeded the ‘minimum discomfort’ threshold of 10.0 in parts of all seasons. The mean index was 11.3, and this did not differ significantly between seasons. The total dry weight of dung beetles at the time of the first influx of bush flies each year was consistently below 3 g/dung pad which was apparently too low to depress bush fly breeding below their replacement level of 3%. The mean annoyance index of 3.1 for the 1990–91 season was significantly lower than for the pre-introduction period and the total dry weight of beetles during November-December exceeded 3 g/dung pad on all sampling occasions. In the 1991–92 and 1992–93 seasons fly annoyance indices reverted to pre-introduction levels (seasonal means of 13.7 and 7.8 respectively) and total dry weight of beetles was again below 3 g/dung pad when the bush flies first appeared. Survival of immature bush flies in local dung pads remained below the replacement level of 3% during 1990–91, but exceeded 3% on two occasions during 1991–92. Apart from 1976–77, when mean catches of native dung beetles (O. australis and O. granulatus) were exceptionally high, mean catches of native dung beetles during pre- and post-introduction years were very similar, but the mean dung beetle biomass increased following the establishment of exotic species.