The relationship between dung quality and oocyte resorption in laboratory and field populations of Lucilia cuprina

Oocyte resorption in Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae) is indicative of protein shortages during ovarian development. It is commonplace in field populations and is thought to reflect the species’ dependence on sheep dung as its primary source of protein. To test this proposition, resorption was monitored in flies fed with sheep dung collected when pastures varied from lush to drought affected. Laboratory assays showed that the proportion of females that became gravid, their rate of ovarian development, and the size and number of oocytes matured all decreased significantly as the protein content of the food source decreased. Conversely, the number of oocytes resorbed increased as dung protein decreased. However, estimates of dung quality (DQ), as derived from a pasture growth–DQ model, were not informative in explaining the seasonal or regional prevalence of resorption in flies collected over several years in three widely disparate sheep‐grazing areas. Recalibration of the DQ model to provide daily estimates of dung protein, which were then used to predict the incidence of oocyte resorption at different times of the year, also failed to show any systematic effects. There was, however, a clear tendency for this model to underestimate the extent of resorption in field populations. Because wild flies would have ready access to a wide variety of food sources, many of which would have been more nutritious than sheep dung, this finding is contrary to expectation and hence the nutritional role of sheep dung merits further study.