SWARMING OF CULICOIDES-BREVITARSIS KIEFFER (DIPTERA, CERATOPOGONIDAE) WITH REFERENCE TO MARKERS, SWARM SIZE, PROXIMITY OF CATTLE, AND WEATHER

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 ms-1 but was reduced to nil at 1·91 ms-1. Temperature, humidity, cloud cover and the presence of direct sunlight did not influence the probability that swarms would form. © 1979 CSIRO. All rights reserved.