INSECTS AFFECTING FOREST TREES. 



495 



Ambrosia Beetles or Wood Borers. The preceding forms all confine their 

 operations very largeh" to the inner bark and sap wood and either assist in destroy- 

 ing the living tree or hasten the removal of its bark. The species next to be con- 

 sidered operate in the wood and prefer to enter such tissues when exposed and are 

 therefore followers of the preceding forms. 



A'yiotcnis bivittatiis Kirby. 



.Small, round, black holes may occasionally be observed in the exposed wood of 

 various coniferous trees and on cxamininir them more closely it 



FIG. to. XYLOTE RUS 

 BIVITTA TUS. 



by the writer in various trees in the Adirondack region. The 

 galleries are characterized by a main burrow entering the wood 

 vertically for a short distance and then giving off brandies on 

 either side which run parallel to the lines of growth and each of 

 these galleries lead into a series of vertical brood chambers in 

 which the young are reared. 



The adult is a stout, brownish-black beetle measuring a little 

 over 1-8 of an inch in length. The form of the antennae, the 



, . . f ^ 1 , AFTER HUBDARD, I'. .S. DEPT. 



sculpturing of the prothorax and the markings of the wing agr., div. ent. dul. 7, 

 covers are shown at fio-ure 10. *" *' ''' 



Gnathotricliiis matcriarius Fitch. 



W^'^'f-^T » This is another of the wood boring beetles which is also known 

 as an ambrosia beetle because of its living upon a cultivated fungus 

 termed Ambrosia. This insect was taken b\- the writer in August, 

 1900, in the stump of a white pine which had been cut between 

 September and December of the previous year. The bark had fallen 

 from the stump and the wood had evidently weathered for some 

 time, as its surface was discolored and black. It was ver\- probably 

 dead when cut. This form was also found in considerable numbers 

 in a dead pitch pine at Manor, in October of the same year. 



The beetle is a rather slender, cylindrical, brownisli-black insect, 

 about J8 of an inch in length and with yellowish legs. The globular 

 antennae, the sculpturing of the thorax and the linear dottings of the 



FIG. II. GNA- 

 THOTRICHUS 

 MA TERIA RIUS. 



AFTER HUBBARD, 

 U. S. DEPT. AGR., 

 DIV. ENT. BUL. 7, 

 N. S. '97. 



,'insj covers are well shown in figure ii. 



