The successful construction of an egg chamber by nesting turtles in coral sand requires that sand slippage be prevented. The factors preventing this are presence of sufficient moisture and/or tree rootlets. Under average conditions of tree rootlets, if the sand was moist enough for the turtle to successfully dig a chamber it contained an adequate water content for incubation. Chlorinity values of natural nests were very low, averaging about 50 mgCl—/kg. At the time of construction natural nest temperatures were about 25%C but metabolic heating increased this by approximately 6°C towards the end of the incubaton period. Under experimental conditions high incubation success was obtained at temperatures of 27, 30 and 32oC. No eggs hatched at 15, 20 and 38C. Eggs incubated at 30°C in sand containing 365 and 730 mgCl—/kg successfully hatched (although percentage hatch decreased with increasing chlorinity) indicating that chlorinity in the natural nest was not a limiting factor.

Observations on the biology of the egg, larval, pupal and adult stages of the bushfly are presented. Many major physiological and behavioural responses and the survival of individuals seem to depend on the temperature and moisture conditions of the environment, and on the quality of animal dung available as food for the larvae. The seasonal distribution of bushfly in Australia seems to be determined directly by this dependence. Temporarily unfavourable areas are apparently repopulated by long distance displacement of adults. No diapausing or other stage resistant to adverse conditions, is known.

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The morphometric cline in bushfly samples collected from north to south in Australia (Paterson and Norris 1970), seemed to throw doubt on the hypothesis that bushflies died out during the southern winter and that northern flies dispersing southwards repopulated the region each s ring (Hughes 1970). The occurrence of the cline of increasing from-ratio of the male b u s h e s from north to south was confirmed in three regions of northern Australia during the winter. However, a seasonal pattern with ratios highest in mid-winter was demonstrated in southern Queensland, and as all these northern winter populations had higher ratios than those of the Canberra populations in summer, the effect of temperature was investigated experimentally. Significant direct effects of temperature during immature development, on the frons-ratio were shown. Limitation of the period of treatment indicated that the sensitive stage occurred during development within the puparium. As temperatures are on average hotter in the north than in the south of Australia, the observed cline in the museum collections is not surprising. The situation is not incompatible with a north to south dispersal in spring.