Abstract
KOYAMA, Juro (Univ. Tohoku, Sendai) The swarming behavior of Fannia scalaris FABRICIUS with special reference to the swarming individual number. Jap. J. Ecol. 12,11-16 (1962). Observations and experiments were made on the swarming behavior of Fannia scalaris FABR. under the willow street tree in Sendai from July to August in 1957. The adults of Fannia scalaris FABR., most of which are males, fly about in a swarms under the crown of the willow street tree. Mating is often observed among the swarming flies. It is characteristic that swarming males frequently pursue each other. Besides, many males and females rest and feed on the leaves and branches of the tree. The diurnal rhythm in the number of swarming individuals is bimodal, that is, numerous in the morning and also in the evening when they expand their swarming range. It seems that the present daily rhythm depends upon the environmental conditions, especially the light condition. It is noticeable from the viewpoint of the population ecology that coaction among the swarming flies seems to relate closely to the limitation of the swarming individual number. Experiments were made to ascertain the above assumption, and the results obtained were : (1) Fluctuations of the swarming individual numbers at two adjoining trees were parallel to each other. (2) When the swarming flies under the crown of a tree were artificially removed, they become replaced by the flies which came from leaves or branches of the same tree. From the above, it is suggested that the swarming individual number is limited by a certain mechanism, seemingly related with the interaction among swarming flies. It is considered that the mechanism mentioned above is common at least to the adjoining trees.
