The effects of competition and larval habitats on populations of the Australian sheep blowfly Lucilia cuprina (Wiedemann)
Creators: name: Williams, H
Publisher: name: University Of Tasmania
Year: 2023

description: The effects of competition on <i>Lucilia cuprina</i> with particular reference to the success of this species in carrion breeding in Tasmania was investigated. The spatial and temporal interaction of the necrophagous fly guild was studied in the main sheep raising areas of the state, and laboratory studies were used to examine the effects of larval competition on life history parameters.The field study showed that <i>Chrysomya rufifacies</i> and <i>Chrysomya varipes</i> had a restricted distribution both geographically (occurring in the northern and central areas of the state) and seasonally (first occurrence being usually in mid- to late summer). This was thought to have particular significance to the success of<i> L. cuprina</i> breeding in carrion as the presence of these species tends to supress the number of its larvae emerging from carrion. A series of carrion experiments were designed to assess the success rate of <i>L. cuprina</i> breeding in the presence and absence of <i>Ch. rufifacies</i>. It was found that in the absence of <i>Ch. rufifacies</i> some<i> L. cuprina</i> were seen to emerge from carrion. The temperatures generated within a carcass were monitored and although high temperatures were generated they were within the thermal tolerance of <i>L. cuprina</i>. There was no correlation between the abundance of species emerging and the abundance of species trapped adjacent to the carcasses.The fine scale distribution of <i>L. cuprina</i> was found to be highly correlated with the presence of both live sheep and sheep carcasses. It had a strongly clumped distribution with several strong nodes of abundance within the trapping area (1km<sup>2</sup> of sheep pasture). All of the other species studied showed a high correlation with sheep carcasses but not with live sheep.Laboratory studies were conducted to simulate competition in both carrion and myiasis. These studies showed that <i>L. cuprina</i> had a considerable capacity for compensating preadult mortality by sacrificing adult size. In artificial carrion, adult size and mortality (preadult and adult) were found to be related to the initial larval density. Development rates were generally increased with decreased adult size.Induced myiasis using a range of larval densities showed that adult size and preadult mortality were independent of initial density. Flies emerging from the induced myiasis experiments were in the larger range of adult sizes. Flies emerging, from the artifidal carrion experiments covered the whole range of adult sizes. This observation led to the analysis of the field population for size related effects of competition.It was suggested that the general size distribution of flies was related to the alternative larval habitats. Using this general rule it was concluded that at least 18% of the field population studied originated from conditions of high larval densities and therefore, probably from carrion breeding. This conclusion was supported by the observation that the size distribution of adult <i>L. cuprina</i> emerging from carrion reflected high larval densities. A high proportion of the population was found to be resorbing eggs and this was assumed to indicate a severe shortage of suitable oviposition sites.A major study of the size and age composition of the field populations of <i>L. cuprina</i> was done in the hope that useful data relating to the characterisation of cohorts could be found. This work was largely unsuccessful due mainly to inherrent errors in the aging technique.A simple simulation model was constructed to assess the affects of larval competition on the reproductive fitness of the adult population. This showed that potential reproductive fitness increased with increased competition (and consequently decreased adult size). This result demonstrated that competition occurring in carrion may increase the reproductive potential of the flies emerging, although other factors such as mobility (and thus the probability of a successful oviposition) may be reduced. It was concluded that factors other than adult size (such as number and reproductive potential) should be considered when assessing the contribution of carrion breeding to the persistence of <i>L. cuprina</i> populations.