Researches on North American Acridiidae

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Carnegie Institution of Washington, 1904 - Grasshoppers - 55 pages
 

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Page 24 - ... The solution of this problem lies in the arrangement of the Acridiidae in the two groups, campestral and sylvan, and the factor involved is, adaptation of structure to habits brought about by a sylvan environment. This has caused a change in structure through disuse of the organs of flight. In short, Brachypterism in locusts is a more complete adaptation to a leaping mode of progression brought about by life in situations where flight is difficult or impracticable, and consequently disadvantageous....
Page 26 - The fact that the heavier-bodied female is more frequently or completely brachypterous than the male and that the tegmina in the latter sex when used as musical instruments are retained in a less degenerate condition (even when entirely useless in flight), confirms this explanation of brachypterism. "BURNING OVER" AS A FACTOR IN DISTRIBUTION. A factor which must seriously affect the distribution of some species is the widespread custom of " burning over" the mountains to improve the range for stock.
Page 25 - On close analysis it is found that Orthoptera frequenting habitats involving passage • over open spaces of considerable extent, such as fields, between trees in forests, and bushes or thickets in deserts, are usually long-winged, flying species; and others dwelling in an environment of more or less dense, intricate, interlacing vegetal growth, be it sub-alpine or tropical, in forest or swamp — or in burrows, crevices, etc.
Page 25 - On the other hand, if uniformity of habits characterizes a group, similarity of structure accompanies it, as witness the Oedipodinae, a subfamily characteristic of open, more or less arid surroundings, inhabiting barren fields and washes, the drifting dunes of the seashore, or bare crags of mountain summits, shy and wary of approach, seeking safety in flight, and with few exceptions equipped with large and powerful wings.
Page 44 - Facial costa widest opposite base of antennae, equalling interspace between eyes, with convex sides convergent above and below, subparallel in lowest portion. Tegmina broadly oval with rounded apex, shorter than pronotum. Abdomen of male less upturned at tip than in pusillus; furcula well-developed, flattened or digitate; supra-anal plate triangular, its breadth nearly or quite equaling its length, the apex rounded, acute.
Page 51 - The three species, — islandicus, celatus, and sylvestris — are evidently nearly related descendants of the same parent form, modified by isolation. Intergrades may yet be discovered. The male from Pineola is included with some doubt owing to differences in structure and season.
Page 58 - Pronotum broad with flattened disk, subangulate at junction with lateral lobes, and moderately convex hinder margin, the mid-carina distinct on the metazone, absent from prozone. Prosternal spine short and variable, usually conical with acutely pointed tip but sometimes much broadened laterally with wide, bluntly rounded apex. Mesosternal interspace slightly transverse in the female, narrower than the lateral lobes...
Page 51 - This species also is a near relative of islandicus BlatchL, differing chiefly in the form of the male cerci, which, while of the same general structure, are narrower at base and have the distal half bent slightly upward and drawn out into a slender, compressed, substyliform tip, the whole appendage being once and three-quarters or twice as long as the width of base.
Page 57 - Hind femora stout, very obliquely bif asciate with fuscous. Hind tibiae glaucous, flavescent at base and tip, with black-tipped spines. " Male abdomen subclavate, the subgenital plate and preceding segment tumescent, broader than deep, and greatly elongated, the former elongate scoop-shaped, bluntly rounded at apex, its sides a .little convex, especially at base. Supra-anal plate broader than long, somewhat trilobate at end by reason of deep, subapical lateral emarginations, the apex acutely pointed...
Page 49 - A short- winged species related to and resembling scudderi but with the cerci shorter, about as long as their basal breadth, equalling three-fifths of the supra-anal plate, triangular, acutely pointed, the sides straight or a little sinuous by reason of convexity of base...

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