Economic entomology for the farmer Economic entomology for the farmer and the fruit grower, and for use as a text-book in agricultural schools and colleges; . economicentomolo00smit Year: 1906 132 AN ECONOMIC ENTOMOLOGY. and we find differences in the form of the honey-tubes which are of generic or even sub-family value. Thus, we have some species of Pemphigus entirely without them, or with very small, mere tubercle-like structures. Tliey live on a variety of trees, but perhaps more abundantly on poplar, and make galls, which are sometimes spherical and nearly half an inch in diameter. If we
Economic entomology for the farmer Economic entomology for the farmer and the fruit grower, and for use as a text-book in agricultural schools and colleges; . economicentomolo00smit Year: 1906 132 AN ECONOMIC ENTOMOLOGY. and we find differences in the form of the honey-tubes which are of generic or even sub-family value. Thus, we have some species of Pemphigus entirely without them, or with very small, mere tubercle-like structures. Tliey live on a variety of trees, but perhaps more abundantly on poplar, and make galls, which are sometimes spherical and nearly half an inch in diameter. If we cut one of them after midsummer, we find it full of plant-lice, Fig. 96. Cock's-comb gall on elm, Colopha nlmicola.—a, elm-leaf showinc; galls; b, winter egg, covered by the skin of the true female; c, larva just hatched ; d, pupa; e, winged adult. the progeny of the single specimen which caused the growth of the gall early in the season. There are many other gall-producing lice, perhaps the best-known being the Colopha ulmicola, found on elm, and forming the 'cock's-comb' gall. The popular name fairly describes the appearance of the abnormal growth, which is an inch or more in length and about one-quarter of that in height. None of these gall-making species are abundant enough to be seriously troublesome ; but quite the contrary is true of the
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