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| Fig. 37.—Phryneta aurocincta. West Africa. | |
The Bruchidae, or seed-beetles, agree with the two preceding families in tarsal structure; the head is largely hidden by the pronotum, and the elytra are short enough to leave the end of the abdomen exposed (fig. 38). The development of the pea and bean-beetles has been carefully studied by C. V. Riley, who finds that the young larva, hatched from the egg laid on the pod, has three pairs of legs, and that these are lost after the moult that occurs when the grub has bored its way into the seed. In Great Britain the beetle, after completing its development, winters in the seed, waiting to emerge and lay its eggs on the blossom in the ensuing spring.
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| Fig. 38.—Bruchus piei (Pea Beetle.) Europe. | Fig. 39.—Platyrrhinus latirostris. Europe. |
Rhynchophora.—The Rhynchophora are a group of beetles easily recognized by the elongation of the head into a beak or snout, which carries the feelers at its sides and the jaws at its tip. The third tarsal segment is broad and bi-lobed, and the fourth is so small that the feet seem to be only four-segmented. There are six malpighian tubes. The ventral sclerite of the head-skeleton (gula), well developed in most families of beetles, is absent among the Rhynchophora, while the palps of the maxillae are much reduced. The larvae have soft, white bodies and, with very few exceptions, no legs.
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| Fig. 40.—Brenthus anchorago. Tropical Countries. | Fig. 41.—Otiorrhynchus ligustici. Europe. | Fig. 42.—Lixus paraplecticus. Europe. |
Of the four families included in this group, the Anthribidae (fig. 39) have jointed, flexible palps, feelers—often of excessive length—with a short basal segment, and the three terminal segments forming a club, and, in some genera, larvae with legs. There are nearly 1000 known species, most of which live in tropical countries. The Brenthidae are a remarkable family almost confined to the tropics; they are elongate and narrow in form (fig. 40), with a straight, cylindrical snout which in some male beetles of the family is longer than the rest of the body.
| Fig. 43.—Scolytus ulmi. (Bark Beetle). Europe. |
The Curculionidae, or weevils (q.v.), comprising 23,000 species, are by far the largest family of the group. The maxillary palps are short and rigid, and there is no distinct labrum, while the feelers are usually of an “elbowed” form, the basal segment being very elongate (figs. 41, 42). They are vegetable feeders, both in the perfect and larval stages, and are often highly injurious. The female uses her snout as a boring instrument to prepare a suitable place for egg-laying. The larvae (fig. 3) of some weevils live in seeds; others devour roots, while the parent-beetles eat leaves; others, again, are found in wood or under bark. The Scolytidae, or bark-beetles, are a family of some 1500 species, closely allied to the Curculionidae, differing only in the feeble development of the snout. They have clubbed feelers, and their cylindrical bodies (fig. 43) are well adapted for their burrowing habits under the bark of trees. Usually the mother-beetle makes a fairly straight tunnel along which, at short intervals, she lays her eggs. The grubs, when hatched, start galleries nearly at right angles to this, and when fully grown form oval cells in which they pupate; from these the young beetles emerge by making circular holes directly outward through the bark.
Bibliography.—In addition to what may be found in numerous important works on the Hexapoda (q.v.) as a whole, such as J. O. Westwood’s Modern Classification of Insects, vol. i. (London, 1838); J. H. Fabre’s Souvenirs Entomologiques (Paris, 1879-1891); D. Sharp’s contribution to the Cambridge Natural History (vol. vi., London, 1899); and L. C. Miall’s Aquatic Insects (London, 1895), the special literature of the Coleoptera is enormous. Classical anatomical memoirs are those of L. Dufour (Ann. Sci. Nat. ii., iii., iv., vi., viii., xiv., 1824-1828); Ib. (ser. 2, Zool.) i., 1834; and H. E. Strauss-Dürkheim, Anatomie comparée des animaux articulées (Paris, 1828).
The wings of Coleoptera (including the elytra) are described and discussed by F. Meinert (Entom. Tijdsk. v., 1880); C. Hoffbauer (Zeit. f. wissen. Zool. liv., 1892); J. H. Comstock and J. G. Needham (Amer. Nat. xxxii., 1898); and W. L. Tower (Zool. Jahrb. Anat. xvii., 1903). The morphology of the abdomen, ovipositor and genital armature is dealt with by K. W. Verhoeff (Ent. Nachtr. xx., 1894, and Arch. f. Naturg. lxi., lxii., 1895-1896); and B. Wandolleck (Zool. Jahrb. Anat. xxii., 1905).