INSECTS FEEDING ON BARK AND DEAD WOOD. 173 



THE CYLINDRICAL BARK-BORER. 



(Rypothenemus eruditus Westwood.'i 

 [Plate XIV, Fig. 1.] 



This minute beetle is frequently an object of suspicion from its pres- 

 ence in great numbers in twigs killed by dieback. Jt is 1.6 llim ( T ^ inch) 

 in length, dark brown in color, cylindrical, and obtusely rounded at 

 both ends. Under a lens it has a hoary appearance, owing to the short, 

 stout hairs with which all parts of the body are clothed. On the wing- 

 cases these stout hairs are arranged in numerous longitudinal rows, 

 and the interspaces between the rows of hairs are deeply and coarsely 

 pitted or punctate. The head is directed downwards and is not seen 

 from above. The declivity of the thorax above the base of the head is 

 covered with minute tooth like asperities. 



The larva as well as the beetle itself feeds upon dry corky wood and 

 bark of various trees, and upon plants having soft or porous tissues, such 

 as are found in the Grape and many other vines. They riddle the dead 

 wood and bark with galleries, and quite rapidly reduce it to powder. 



In the Orange their galleries are seldom found in solid wood, but in- 

 variably occur in the bark and in small twigs when from any cause 

 they have been deprived of life and become dry. Succulent shoots 

 killed by frost or disease attract the beetles in great numbers as soon 

 as they become dry and brittle; but no part of the tree is attacked as 

 long as it retains its sap or remains moist. The insect is therefore en- 

 tirely harmless in its operations, and beneficial rather than injurious to 

 vegetation. 



Life-history. The larva of Hypothenemus is a minute white grub, 

 with a thick and stout cylindrical body, strongly curved, and without 

 legs or other organs of locomotion, save that by the contractile move- 

 ments of its body joints, it is enabled to crawl slowly through its bur- 

 rows. The head is small, and all the parts surrounding the mouth, with 

 the exception of the pair of stout jaws, are so minute that they can be 

 discerned only after careful dissection upon the stage of a microscope. 



The family Scolytidw, to which this beetle belongs, number in the 

 United States at least two hundred species,* divided among numerous 

 genera. All of them have wood boring habits, and members of the same 

 group resemble each other closely. The Iarva3 of the different species 

 are for the most part indistinguishable ; the points of difference, if any 

 exist, are so minute that they have escaped observation. 



The pupa is formed in a little cell, walled off from the galleries made 

 by the larva. It shows the form of the beetle, and is white, turning 

 brown as it approaches maturity. 



The eggs are white, oval in shape, and are scattered by the mother 

 either singly or in little groups at random in the galleries which she 

 excavates. 



"About one hundred aud seventy species have been described. 



