Schädliche Blattläuse in den Tropen und Subtropen unter besonderer Berücksichtigung von Rassendifferenzierungen

Summary Most of the aphids being pests on cultivated plants in the tropics and subtropics are distributed over wide parts of the earth. Such aphids partly (I) possess exclusively the anholocyclic mode of life, and they can persist in regions with cold winter only by the presence of suitable host plants in greenhouses. Rhopalosiphum maidis (Fitch) flies from southern countries to central Europe where it occurs only during summer and fall because it does not overwinter there. Other aphids of worldwide distribution (II) are living anholocyclically in the tropics and subtropics; in the temperate zones, however, they are mainly represented by biotypes or subspecies accomplishing the holocycle. Further differences consist in that the anholocyclic forms show a more extended host range than their northern holocyclic representatives. Such differences are either gradual, e. g. Myzus persicae (Sulz.) and Lipaphis erysimi (Kalt.), or alternative, e. g. Aphis craccivora Koch, Aphis frangulae Kalt. and Schizaphis graminum (Rondani). Obviously the interaction of the sexual morphs in the regions with cold winter considerably increases the effect of ecological and ethological isolation which leads to the preference and finally to the restriction for a limited number of food plants. The same principle seems to be efficacious for the speciation. This is demonstrated by M. persicae and A. craccivora and their nearly related oligophagous and monophagous species.