The value of cattle dung as a food resource for the bush fly Musca vetustissima (Walker) in the winter rainfall agricultural region of southwestern Australia was assessed by bioassay in the laboratory. The size (headwicJth) of adult females was measured from flies reared on different samples of dung. Variation in size correlated with seasonal patterns of pasture growth, larger flies being produced during the growing season from autumn to spring. Size declined with senescence of annual pastures in late spring and early summer, occurring later in southern areas where the growing season was longer. After pasture senescence, dung from shorter growing season areas usually produced larger flies, apparently a result of the inverse relationship between digestibility of feed and length of growing season. Dung from irrigated perennial pastures never prochued flies as large as that from anmuil pastures but generally high values were sustained during summer. Grazing of cereal stubble and feeding of hay in annual pasture areas during summer usually caused some increase in fly size. A spontaneous resurgence in the size of flies often occurred several weeks after pasture senescence and was attributed to more thorough digestion as a result of reduced intake of less palatable dry pasture.
A range of densities of bush fly (Musca vetustissima) eggs and dung beetle (Onthophagus binodis) adults were placed on either nutritious spring or poor summer dung in the laboratory at 25 ~ Intra-and interspecific competition were greater for flies in summer dung than in spring dung, and intra-and interspecific competition were greater for dung beetles in spring dung than in summer dung. In summer dung fly size and survival were influenced by both beetle and fly densities. Flies in summer dung were smaller, and below a headwidth of about 2.0 mm there was a correlation between size and survival. Mortality was probably due largely to death of larvae. Also beetles produced very few brood balls, and shredded this dung, particularly at high densities. In spring dung, beetle brood ball production which was greater was reduced by both beetle and fly densities, and beetles left the pads earlier at high fly densities. Fly survival was influenced by beetle density, but less than in summer dung, and not by fly density. Mortality was probably caused by death of eggs. These data support field observations that dung beetles cause higher fly mortality in summer dung than spring dung. Entomol. exp. appl. 41:83 90, 1986 9 Dr W. Junk Publishers, Dordrecht -Printed m the Netherlands
The mortality of eggs and larvae of Musca vetustissima Walker, caused by two scarabaeine dung beetles was measured in the laboratory in favourable cattle dung at 23°C. Eggs and larvae less than one day old were the main stages killed in the dung. Mortality from beetles that entered dung immediately after fly oviposition was higher than that from beetles that entered the dung one or three days later. The results also indicated that there are differences between species of dung beetles in the mode of action against the fly. The smaller beetle species, Onthophagus binodis (Thunberg), at densities of 120 beetles/pad caused increased mortalities of 12% of fly eggs and 11% of young larvae but did not affect older larvae, while the larger species, O. ferox Harold, at densities of 48 beetles/pad caused no extra mortality of eggs but did cause an increased mortality of 47% of young fly larvae and 61% of older larvae.
The stages of bush fly Musca vetustissima Walker, killed by the dung beetles, Onthophagus binodis Thunberg and Onitis alexis Klug, at low and high densities were measured in cattle dung of low nutritive value. A high level of M. vetustissima mortality occurred in the presence of Onitis alexis and Onthophagus binodis in experiments both in the laboratory at a constant 25 °C, and exposed to summer fluctuating temperatures outside. The K values for total eggpuparia mortality increased curvilinearly with increasing log ]0 beetle numbers. The mortality of older larvae, k y was most closely correlated with total mortality, K, where b = 0.720 and r 2 = 0.931, while a lesser but significant correlation was obtained with mortality of young larvae, k 2 , where b = 0.291 and r 2 = 0.645, but no correlation was obtained with egg mortality, k ]7 where b = -0.010 and r 2 = 0.058. It is predicted that in unfavourable dung which occurs during summer, mortality of older bush fly larvae will be the key mortality caused by scarabaeine dung beetles.
\ Females of Musca vetustissima Walker in the first ovarian cycle and of a wide range of body size were fed a range of measured quantities of proteinrich liver exudate. For a given amount of exudate, a greater proportion of large flies than of small ones matured oocytes; for a given size of fly, the proportion that matured oocytes increased with the amount of exudate ingested. Additionally, large flies matured more oocytes on less exudate than did small flies, which had fewer ovarioles.
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