THE BRONZE BIRCH BORER 7- 



from May i5th to June ist, or even later. In 1900 Adams reported that none 

 of the beetles had emerged by June 3rd. The beetles feed on tender foliage, evi- 

 dently preferring other trees like the willow and poplars, as Larsen has shown. 



Egg-laying. I have not seen the eggs of this bronze birch borer as I 

 could not induce the beetles to lay eggs in my cages, but Larsen was more 

 fortunate and obtained evidence that they were laid in crevices of the bark. 

 He states that beetles ''confined in a glass jar were found to be depositing 

 eggs on June 8th, and for a week or more afterwards. Pieces of fresh limbs 

 were supplied, but the insects did not deposit their eggs upon these, but moved 

 about feeling for crevices with their long prehensile ovipositor and having 

 found a place, such as between the glass and the lower part of the cork or 

 under a piece of wood, from five to ten or more eggs were put in one place. 

 Copulation had gone on for sometime before this. Great activity was exhib- 

 ited during the copulation and egg-laying. No observations were made on the 

 development of the eggs. " It is unfortunate that the eggs were not described. 



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 followed from end to 

 end, as described on page 68 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 under 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. 



Work of the borer. The beginning of the newly-hatched borer's burrow- 

 ings in the bark in June have just been described in the preceding paragraph. 

 And its later work as it industriously tunnels its way, zigzagging around and 

 through the branches has been described on page 68. 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. 



Length of the life-cycle. Although no one has followed this birch pest 

 through its whole life, all the recorded evidence and all my observations indi- 

 cate a yearly life-cycle.* I have just made a careful examination 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 indi- 



* Most of the species of Agrilut* 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 Agrilus sinuatus, both European species, the latter now an 

 American pest also. But our native Agrilus bilineatus and Agrilus ruficollis seem to have 

 a yearly life-cycle. 



