Bleeding Sap Preference of the Drosophilid Flies

Abstract

1) The preference of sap eating drosophilid flies to fruit in nature was investigated, locating fruit traps near and remote to a bleeding Quercus tree. The fruit eaters are thought to be selectively advantageous in having higher potentiality of utilizing diverse kinds of food environments, as compared to the sap eaters. Evident replacement due certainly to competition during about ten years was shown between some closely related species having equal sap preference. 2) Within a year the ecological niche occupied by each species tended to become broader in the warmer season, due probably to the saturation of the primary habitats by the existing populations and to the invasion of excessive populations into the poorly occupied microgeo-graphical or microecological niches of the secondary habitats, thus resulting a balanced cohabitation. 3) The sex ratio (♀/♂×100) of the flies collected either at sap or at fruit was higher than that of the flies collected at both sap and fruit. Seasonal fluctuation of sex ratio was roughly proportional to the population size under coexistence of sap and fruit sources. It became, however, increasingly high in the later seasons, despite the population size was decreasing, under separated food sources. The establishment of breeding sites for the occupants seems to have been remarkable in this case. 4) The sap exudation is thought to have been an original diet for drosophilids, because the essential sap eaters are apt to be primitive in morphological features, relatively narrow and scattered in distribution and bradytelic in presumed phyletic changes. 5) Some morphological and behavioral features of adults and larvae adapted to the sap eating nature have been explained. 6) A suggestion was given from standpoint of applied entomology on a controlling effect of the coexistence of wild and cultivated food sources upon the herbivorous insect pests injurious upon these plants. © 1962, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.