246 B. H. GRAVE 



making organ. The larva may therefore appropriately be called 

 a leaf miner. Late in the season, at the time the leaves fall, 

 it emerges and enters the ground. After burrowing to a depth 

 of between one and one-half and two and one-half inches below 

 the surface, it excavates a little spherical cavity in which it 

 coils up for the winter sleep. 



About the last of May of the following spring (May 25-June 15) 

 the larvae transform into pupae. As yet I have no definite 

 records concerning the date of emergence of the adult under 

 natural conditions, but the indications are that the duration of 

 the pupa is about three weeks or possibly a month in cool weather. 

 Under laboratory conditions it is about three weeks or less. 

 The first beetles may therefore be expected to appear by the 

 middle of June. There is reason to believe that they appeared 

 as early as June 10 in the year 1913, which was a rather early 

 spring for that locality. The number of pupae in the soil was 

 considerably diminished before June 15 and the supposition is 

 that they had metamorphosed. I found no imagoes at that 

 time, how^ever, probably because I did not know what kind of 

 beetle to look for. 



It has not been possible for me to return to Wyoming during 

 the past three years so that it is not known whether the eggs are 

 laid en masse or singly, upon the twigs and leaves. The fact 

 that only one larva, as a rule, attacks a leaf might lead one to 

 suspect that the eggs are laid singly. A number of beetles which 

 were hatched from breeding boxes were kept in captivity and 

 one of them laid eggs ten days after it emerged. It seems likely 

 therefore that under normal conditions the eggs are laid upon the 

 leaves and twigs during the latter part of June and the first 

 part of July and that the larvae enter the leaves soon after, and 

 begin their destructive work. 



The adult beetles, as might be expected, feed upon the leaves 

 of the Cottonwood. They swallow the softer parts and discard 

 the fiber. 



