Biological Notes


    GALL-MAKING INSECTS.—At the St. Louis meeting of the American Association Prof. C. V. Riley read a paper on the gall-making Pemphiginœ. He said that the life-history and agamic multiplication of the plant-lice (Aphididœ) have always excited the interest of entomologists as well as of anatomists and embryologists. The life-history, however, of the gall-making species belonging to the Pemphiginœ has baffled the skill of observers more than that of any other group. Mr. Riley is about to publish some new biological discoveries relating to this family of insects, in connection with a descriptive and monographic paper by Mr. J. Monell, of the St. Louis Botanic Gardens. The paper laid before the Association simply records some of the yet unpublished facts discovered. All of the older writers, in treating of the different gall-producing Pemphiginœ of Europe, have invariably failed to trace the life-history of the different species after the winged females leave the galls, and, with few exceptions, have erroneously inferred that the direct issue from the winged females hibernates somewhere. The most recent production on the subject is a paper published in the present year in Cassel, by Dr. H. F. Kessler, which is entitled the “Life-History of the Gall-Making Plant-Lice, affecting Ulmus campestris.” The author, by a series of ingenious experiments, rightly came to the conclusion that the insects hibernate on the trunk, but he failed to discover in what condition they so hibernate. Led by his previous investigations into the habits of the grape Phylloxera, Mr. Riley discovered, in 1872, that some of our elm-feeding species of Pemphiginœ produce wingless and mouthless males and females, and that the female lays but one solitary impregnated egg. Continuing his observations, especially during the present summer, he has been able to trace the life-history of those species producing galls on our own elms, and to show that they all agree in this respect, and that the impregnated egg produced by the female is consigned to the sheltered portions of the trunk of the tree and there hibernates—the issue therefrom being the stem-mother which founds the gall-inhabiting colony the ensuing spring. Thus the analogy in the life-history of the Pemphiginœ and the Phylloxerinœ is established, and the question as to what becomes of the winged insects after they leave the galls is no longer an open one. They instinctively seek the bark of the tree and there give birth to the sexual individuals, either directly or (in one species) through intervening generations.

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    Biological Notes . Nature 19, 75–76 (1878).

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