The red-legged earth mite, H, destructor, is restricted to the southern parts of Australia having a Mediterranean-type climate, with warm dry summer and cool wet winter. The northern or inland distribution agrees closely with the 205-mm isohyet for the growing season May-October inclusive. The eastern distribution is limited by the quantity of midsummer (December-March) rainfall and agrees closely with the 225-mm isohyet for this period. Other limitations to distribution within these isohyets are imposed by high summer temperatures (mean monthly maximum of hottest month, 33�C). The blue oat mite, P. major, can tolerate a drier climate, reaching a May-October isohyet of about 190 mrn, and a higher proportion of summer rain. This enables it to survive on the south coast of New South Wales and on the northern tablelands of New South Wales as far as southern Queensland, but not in north coastal areas where the midsummer rainfall exceeds about 500 mm. On the evidence available, the likely future movements of these mites both within Australia and overseas are discussed. Vigilance will be needed to prevent H. destructor from becoming a pest in the Americas and in the Mediterranean region.

The occurrence of an aestivating diapause in the eggs of the red-legged earth mite, H. destructor, is established. The production of diapause eggs in females is influenced by the increasing maturity of food plants in the spring. Morphogenesis is resumed following exposure to early summer conditions for 4-6 weeks in the field. In the laboratory, diapause development was achieved by exposing the eggs to various combinations of temperature and relative humidity. The most effective treatment was exposure for 32 days to 52'C and 50% R.H., although diapause development occurred within the temperature range 15-70°C and relative humidity range 10-loo%, and even when the eggs were completely immersed in water. It was most successfully promoted in atmospheres having vapour pressures of about 40 mmHg, at all temperature and humidity combinations. At 20% R.H., diapause development was relatively slower than at humidities above and below this, whereas tolerance to high temperatures was greatest at this humidity.Diapause eggs were not harmed either by complete immersion in water or by periodical desiccation and re-moistening.

After diapause development is complete, moistened aestivating eggs of H. destructor develop successfully within the temperature range 5-20.5C. The rate of development up to the deutovum stage increases with temperature up to about 20C and then rapidly decreases. Eggs will tolerate temperatures between 25 and 31.5C for up to 53 days without undergoing morphogenesis, but this treatment retards subsequent development at 16C. Exposure to alternating temperatures accelerates the rate of development but, if the higher temperature exceeds 20.5C, development is retarded. The effect of temperature on the rate of development within the deutovum stage is similar to that on non-diapause winter eggs throughout their morphogenesis. Air-dry eggs will tolerate temperatures up to 75C but moist eggs are killed by exposure for 1 day to 45C. This high temperature tolerance, together with the limitations on development imposed by temperature, ensures that the aestivating eggs do not hatch before early autumn, even in the event of unseasonal summer rain. The temperature response curve and its ecological significance are discussed briefly.

The changes in numbers of Sminthurus viridis (Collembola: Sminthuridae) in pastures in Western Australia were studied for 9 years on one site and for shorter periods on other sites. Five factors affecting numbers are described: (1) weather, (2) soil type (3) botanical composition of the pasture, (4) predation by Bdellodes lapidaria (Acarina: Bdellidae), and (5) eating of dead bodies by newly hatched nymphs. Weather is generally favourable for the active stages during autumn, winter, and spring. In the summer, the species is maintained by aestivating eggs. Dry periods during the winter months sometimes cause high mortalities. Soils containing a high silt-plus-clay content support higher numbers due mainly to increased oviposition. Flea densities increase more rapidly where there is a high proportion of broad-leaved plants, such as clover and capeweed in the pasture. Grassy areas are not favoured. Predation by B. lapidaria effectively reduces numbers. The presence of more than 20 B. lapidaria per square metre early in the winter prevents any outbreak of fleas later in the season. Bdellodes lapidaria numbers increase in response to an increase in flea numbers. An irregular predator-prey cycle is set up in this way. Density-induced mortality, resulting from the newly hatched nymphs eating the bodies of recently dead fleas, plays a dominant role at high densities. This process operates continuously though at decreased intensity at lower densities. When newly hatched nymphs feed upon dead nymphs and adults they ingest materials which cause early death. Sometimes this may lead to a dramatic collapse of the population. Fleas from high-density populations usually contain large quantities of uric acid in their "fat-bodies". It is suggested that death of the mature fleas at high densities is hastened through the storage of excessive amounts of waste material. Death of the young nymphs feeding upon the dead bodies may be brought about by the ingestion of these waste materials, although this has yet to be proven.

The distribution and seasonal activity of Onthophagus granulatus Boh. was studied at two sites in eastern Australia. It is a univoltine species, with peaks of activity in spring and early summer. Breeding cycles and periods of stress were demonstrated by the proportions of newly emerged, nulliparous and parous beetles and those resorbing oocytes. The optimum temperature for brood production was 25°C. The threshold of development was 11·3°C, and 495 day-degrees C were required for development from egg to adult. Dung quality and drought were important factors affecting survival and brood production in the field. The distribution of the species in south-eastern Australia is limited by summer rainfall and temperature.