Numbers were recorded of adult C. brevitarsis emerging from standard samples from variously treated dung pats. Adult emergence was a more efficient technique than the extraction of immatures. Emergence increased linearly by from three to four ovipositions per pat per day over the first 7 days of exposure of pats in the field. Oviposition occurred throughout the diel, maximum 1400-1800 h and minimum 0000-0700 h. Emergence began 11 days after pats were exposed and was completed by day 24. From days 12 to 24 numbers emerging halved every 1.7 days. Eggs were deposited all over the upper surface of pats with greatest density at the centre. Number emerging per unit area was independent of pat size. Adults emerged from pats of varying shape in plan view but few from pats sunk flush with the ground, surrounded by a sleeve, or subjected to heavy rain within 24 h of deposition. It is suggested that emergence rates reflect oviposition rates, and it is concluded that C. brevitarsis orients visually to dung, probably while flying above it. The rounded sides of the pats may be very important.

Swarms of Culicoides brevitarsis Kieff. were examined in the field in south-eastern Queensland, and their markers are described. Flies swarmed over the sunward edge of an area where the intensity of reflected light was very low. The most common markers were shadows cast by clumps of living grass slightly elevated above the sward. The size and density of the shadow were not important within very wide limits. Objects that cast shadows were successfully used to induce swarming. In contrast to most other species, males appeared to fly in all directions in swarms that did not settle on or near their markers as the wind speed increased. The mean size of swarms was 49.7 males and 0.6 females. Females were present in 34.7% of all swarms. Near to cattle, swarms were significantly larger, closer together, lower, and more likely to contain females than elsewhere. The influence of cattle extended 10 m around the animal's head, with all swarms on the sunny side and within 5.4 m of the head. Swarming began about 1 h before sunset, and mostly ceased at or soon after sunset. The probability of swarming during that period exceeded 0.95 when the wind speed was less than 1.11 m/s but was reduced to nil at 1.91 m/s. Temperature, humidity, cloud cover and the presence of direct sunlight did not influence the probability that swarms would form.

Aphytis melinus DeBach was introduced to South Australia, reared in the laboratory, and then released against Aonidiella aurantii (Mask.) on citrus. In tests in nine citrus orchards, 100 adults of Aphytis melinus ensured colonisation during summer and early autumn, 1000 during late autumn, but even that number was insufficient during winter. Colonisation was equally successful whether Aonidiella aurantii was very abundant or very rare. The most efficient method for colonisation was therefore to release 100 adult parasites during summer and early autumn into small populations of A. aurantii. The parasite had dispersed at least three trees from each summer release site after five months, but much less following autumn releases. Ten months after summer release into nine trees of a total of 3330 adults, Aphytis melinus was recovered from 286 out of 354 (80%) trees in one orchard. In a further experiment, numbers of Aonidiella aurantii were reduced from 300-1000 per ISO leaves on five trees to less than 10 per ISO leaves 18 months after the release of Aphytis melinus, whereas on a control tree they increased from S50 to 1450 per 150 leaves over nine of those months.

In C. brevitarsis the mature egg was 290 pm long, average fecundity was 31.3, and duration of oogenesis 30-50 h at 24-26°C. When the first blood meal was consumed oocytes ranged from stage No to I, and 95.8% of females were mated; after a partial blood meal fewer oocytes were initiated and even fewer matured. It is highly likely that C. bre~itarsis is anautogenous. Oocytes develop through the same stages as other Culicoides. Chorion developed well below the sheath in late stage IV, causing a reduction in width of oocytes at maturation. Ansulae develop in the space between the sheath and chorion by outward sclerotization, possibly along pore canals; they vary from tall (8-9 pm) and broad on the concave surface to short (5-6 pm) and narrow on the convex surface; those on the concave surface probably act as a plastron. The sheath surrounding the stage IV oocyte is destroyed during maturation. The secondary oocyte commences development when the primary is at stage 111, and its development is arrested at either stage N or I almost simultaneously with the primary oocyte completing development. Development of the secondary oocyte is initiated but not controlled by development of the primary in the same ovariole.

Longevity of adult Culicoides brevitarsis was determined by keeping laboratory reared adults in cages at 25°C and 75-85% R.H. When allowed access to no food, to water, or to 10% sucrose mean survival times in days were respectively males 1.4, females 1.1: males 1.6, females 3.1; and males 9.0, females 8.6. Flies orientated to water and to 10% sucrose from a maximum distance of 1Omm. Most flies did not stop when they reached the water (mean time stationary=0.3 s) but all stopped, for a mean of 118.8 s, at the 10% sucrose.