Trimerotropis

Abstract: In former papers (White, 1949a and b, 1950, 1951) we have shown that the North American grasshopper genus Trimerotropis may be subdivided into two sections, a \"primitive\" one (A) in which all the chromosomes are acrocentric, and a \"derived\" one (B) in which some of the chromosomes have become metacentric, as a result of structural rearrangements which have transferred the centromeres from near the ends of the chromosomes to some interstitial position. Members of the related genera Circotetti» and Aerochoreutes show the same type of genetic system as the members of section B of Trimerotropis. In order to simplify the terminology, we shall designate the assemblage of forms which possess some metacentric chromosomes as the \"M.e.\" grasshoppers, a term which i~ not intended to correspond to any particular systematic category, but which probably represents a natural phylogenetic group. The M.e. grasshoppers consist, so far as known, of the section B of Trimerotropis, together with the genera Circotettix, Aerochoreutes and an unnamed gen~s which should be created to receive Circotettix maculatus Scudder, a species which is certainly not congeneric with C. undulatus Thomas, the genotype of Circotettix. If any of the Old World Bryodemae should eventually be shown to possess the same type of structural rearrangements in their chromosomes as the above-mentioned forms, they should be included in the M.e. group. STRUCTURAL HETEROZYGOSITY IN NATURAL POPULATIONS OF THE GRASSHOPPER TRIMEROTROPIS SPARSA 1