LARSEN ON A DISEASE OF THE WHITE BIRCH. 47 



parts of Chicago, 111., particularly in Humboldt Tark where many have 

 died and others were in a precarious condition. Upon inquiry it was 

 found that nursery slock had been brought from Rochester, N. Y., and 

 that some of these were infected. Bome specimens were brought here 

 from Rochester for experimenting and planted upon the campus. Upon 

 one of these were found the ridges mentioned above. 



The life history of the beetle as far as observed is this: The eggs 

 are deposited in crevices in the bark in the early summer. Insects con- 

 fined in a glass jar were found to be dej>ositing eggs on June 8, 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 oi' under a piece of wood, from five to ten or more eggs were put 

 in one place. Copulation had gone on for some time before this. Great 

 activity was exhibited during the copulation and egg-laying. No obser- 

 vations were made of the development of the eggs. Fully formed 

 larva' Avere found early in the winter. They remain torpid until 

 spring. 



Larva^. that were still in the winter stage were found until April 12. 

 Shortly after this the pupa stage began to appear and development 

 went on rapidly until May 1, when a few adult insects were taken com- 

 ing out from the burrows. At this date, however, most w'ere still in 

 the pupa stage. Then came a spell of cold weather and not until 

 more than a week later did the insects come out in numbers, many be- 

 ing taken from the burrows as late as May 15. 



That the weather, or rather the temperature, decides the time of 

 development is indicated by the above facts. And it Avas further demon- 

 strated by material kept in the laboratory. Parts of branches con- 

 taining larvae were taken into the laboratory in March and development 

 began immediately and an adult insect obtained in the middle of April. 



The mode of escape of the beetles from the burrows and places in 

 which the larva?, spend the winter is interesting. The larva burrows 

 out near the bark, then turning into the wood at a slight angle an en- 

 larged oblong chamber is formed in which the larva rests and under- 

 goes further development in the spring. The burrow has been carried 

 outwards in a rather sharp curve which brings its end to just beneath 

 the bark beyond the chamber. When the beetle is ready to escape it 

 makes its way to this and, eating through the bark, escapes. The 

 larva is often found doubled up in the chamber. Normally it lies with 

 its ventral side turned outwards and the beetles are found in this 

 position. Some were found reversed and could not escape. The escape 

 is rather laborious as the insect must squeeze its way to the bark 

 and then eating a small hole again squeeze its way through. Beetles 

 are found with the forward parts of their bodies protruding for hours 

 making long rests between efforts to free themselves. There seems to 

 be no rule governing the direction, whether upwards or downwards, 

 in which the head of the insect is turned during development. 



The extent of the burrows is not an easy matter to determine, nor 

 precisely wiiere they take their origin. They are compressed in shape 

 to suit the flattened shape of the larvre. In one place in a slight swell- 



