THE BEETLES AND THEIR HABITS. 

 • The Life Stages. 



The Bark-beetles are small, usually cylindric beetles, from one to nine 

 millimetres in length, and brownish or black in colour when mature. They 

 are found in company with their small, whitish, legless grubs, cutting tunnels 

 in the bark or wood of trees. Figures on plates 4 and 5 illustrate types of 

 the tunnels cut by them. 



In common with other beetles there are four life stages: the egg, the larva 

 or grub, the pupa or resting stage, and the adult beetle. 



The eggs are usually oval, elongate-oval, subglobular, or rarely somewhat 

 elongate; pearly white or translucent and watery; with a very delicate covering 

 when deposited in niches and packed with boring dust, but with a thicker 

 skin when left loose in the galleries (PI. 3, figs. 1,3). The surf ce modifica- 

 tions appear to be of minor importance. They are, of course, very small, 

 but sometimes of an astonishing size in relation to the size of the mother 

 beetle. The eggs of Cryphalus are almost as large as the beetle's abdomen. 



The larvoB are always legless, whitish in colour, with darker, strongly chitin- 

 ized head and mandibles, and with the thoracic segments distinctly larger than 

 the others, in the true bark beetles (PL 1, fig. 2). In ambrosia-beetles of the 

 genera Anisandrus and Xylehorus, the larvae move about freely in the tunnels, 

 and they are more elongate and distinctly more mobile than the others. 



The characters of the larvae will prove of considerable assistance in the 

 classification of the family; and in addition, they are of decided practical value, 

 since not infrequently the larvae alone are obtainable in material sent in for 

 determination. A discussion of the larval characters, however, must be left 

 for a later publication. 



A distinct prepupal, quiescent stage, lasting a few days, is common in the 

 family. 



The pupcB are formed in the ends of the larval mines, sometimes in pupal 

 cells. They are white at first, becoming yellowish before transformation. 

 They are variably armed with spines and stiff setae, and present characters of 

 decided importance (PI. 1, fig. 3). The adults are yellowish when they emerge 

 from the pupal skin, but rapidly become darker in colour, passing through 

 yellow to reddish and dark brown or nearly black. 



PLATE 1. 

 IPID BEETLES, All Greatly Enlarged. (Original.) 



Fig. 1, Dendroctonus monticolae Hopk., upper left. 



Fig. 2, Dendroctonus monticolae Hopk., larva, upper right. 



Fig. 3, Dendroctonus borealis Hopk., pupa, right centre. 



Fig. 4, Pityophthorus nitidus Sw., lower right, 



Fig. 5, Pityophthorus nitidus Sw., details of the pronotum, left centre, autenna incorrect. 



Fig. 6, Pityophthorus nitidus Sw., caudal view of the declivity, lower left. 



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