Karyotype variation in the corn leaf aphid, Rhopalosiphum maidis (Fitch), species complex (Hemiptera: Aphididae) in relation to host-plant and morphology

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Abstract
Rhopalosiphum maidis (Fitch) collected on barley in the northern hemisphere usually has a ten-chromosome karyotype, whereas samples from maize, sorghum and Johnson grass (Sorghum halepense) from all parts of the world commonly have 2n = 8. Samples with other karyotypes (2n = 9, 2n = 11 and 2n = 8 heterozygous for an interchange between the X chromosomes) occur less frequently on these and other species of Gramineae. Multivariate morphometric analysis, principally by the method of canonical variates, indicated that the ten-chromosome form may be regarded as a single clone of R. maidis recognizable by its karyotype and host-plant relationships, although not completely separable by morphology alone from all other clones of this permanently parthenogenetic species complex.