Entomological Notes

Paul S. Welch
1917 Transactions of the American Microscopical Society  
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more » ... out Early Journal Content at http://about.jstor.org/participate--jstor/individuals/early-journal--content. JSTOR is a digital library of academic journals, books, and primary source objects. JSTOR helps people discover, use, and build upon a wide range of content through a powerful research and teaching platform, and preserves this content for future generations. JSTOR is part of ITHAKA, a not--for--profit organization that also includes Ithaka S+R and Portico. For more information about JSTOR, please contact support@jstor.org. AMERICAN MICROSCOPICAL SOCIETY ENTOMOLOGICAL NOTES Parthenogenesis in Aleurodes.-Williams ('17, Journ. Genetics, 6:256-267), in a paper entitled "Some Problems of Sex Ratios and Parthenogenesis," presents results of a study of sex relations in a common and widely distributed white-fly, Aleurodes vaporariorum, which occurs in North and South America, the West Indies, Europe, and New Zealand. This insect has two races, one in England which produces females parthenogenetically, and the other in the United States produces males parthenogenetically. Fertilized eggs yield an equality of the sexes, and since the eggs would produce one sex only if unfertilized, it is argued that there must be two kinds of sperm, both of which develop in equal numbers. The similarity to the case of Phylloxera carycecaulis is indicated, the chief differences being the production of both sexes in sexual families and the absence of regular alternation of sexual and parthenogenetic generations. The occurrence of "male-" and "female-producing" races of a single species, each of different geographical distribution and varying sex proportions, raises the question of their origin. "External conditions may alter the sex ratio in a colony by preventing pairing." The effect of partial or complete failure to pair on the sex ratio in both races is discussed. "Male-producing" species or races are more liable to die out, while in the "female-producing races, the male sex is gradually lost, the race becoming in time completely parthenogenetic." The original home of a species may be indicated by the presence of both sexes, in case it is represented in another locality by only one sex. An illustration is drawn from the Pear Thrips of California, Twniothrips inconsequens, which occurs in the United States, Canada, and Europe. In America, males are not known, but in Europe both sexes are common. This is regarded as evidence that the original home of the species was in Europe and that females carried to Amreica have continued to reproduce parthenogenetically. "Maleness" would be introduced if a male be imported and subsequent mating with a female accomplished. Males might then become quite general. "The resulting events would, however, depend on the sexes produced by fertilized eggs and the relative fecundity of fertilized and parthenogenetic females." Another example closely analogous seems to appear in
doi:10.2307/3221514 fatcat:xltczbtrjvhbznhznyorncqkhq