150 Bulletin :234. 



As further evidence that the eggs are laid several in a place in 

 crevices or rough places on the bark, is the fact that the burrow I fol- 

 lowed from end to end, as described on page 142 and shown in Fig. 32, 

 began at a rough place where a twig had been broken off. And Larsen 

 found that " in one place in a slight swelling on the bark were several 

 small openings, less in diameter than a pin. From these openings burrows 

 were traced. The burrows are at first very small and lie close imdcr the 

 bark and are filled with dark granules." Adams wrote me of a similar 

 observation made in Buffalo early in June, 1899. He " detected the 

 beginnings of the burrows by a slight circular discoloration on the outer 

 bark." 



Thus the evidence indicates that after feeding for a few days, the 

 beetles mate and the eggs are laid early in June in rough places on the 

 bark of the birches, first on the upper branches and later on the trunk. 



JVork of the borer. — The beginning of the newly-hatched borer's 

 burrowings in the bark in June have just been described in the preceding 

 paragraph. And its later work as it industriously tunnels its way, zig- 

 zagging around and through the branches has been described on page 142. 

 Beginning early in June, the borer must work almost incessantly to be 

 able to dig such a tunnel in less than four months, or before October ist. 



Lcmjih of the life-cycle. — Although no one has followed this birch 

 pest through its whole life, all the recorded evidence and all my observa- 

 tions indicate a yearly life-cycle.* I have just made a careful examina- 

 tion of much of the infested portion of a large white birch, and I found 

 nothing but full-grown grubs or borers and exit holes of last year's 

 generation. There were no indications of small or half-grown borers, 

 as there would be if the insect required two seasons to develop. 



Natur.\l Enemies 

 Were it not for the ubiquitous English sparrow, doubtless the wood- 

 peckers would help considerably in reducing the numbers of this bronze 

 birch borer. The sparrows have largely driven the woodpeckers out of 

 city parks and private grounds. During most of its life, or for about 

 eleven months in a year, the borer is just under the bark wdiere the birds 

 could easily get at it. Adams observed one of the common woodpeckers, 

 probably the hairy woodpecker, feeding quite extensively upon the grubs 

 in Buft'alo. 



* Most of the species of Agrilus, both European and American, whose life- 

 history has been fully worked out, require two years to complete a life-cycle or 

 generation. This is true of Agrilus viridis and .-Igriliis siiiuatus. bntli European 

 species, the latter now an American pest also. But our native Agrilus bilincatus 

 and Agrilus ruficollis seem to have a yearly life-cycle. 



