28 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



The number of mines per leaf at this time averaged from 15 lo 18. 

 By August' 4 pupse had largely yielded moths, and eggs were 

 again very abundant, a few having already hatched. By August 26 

 another generation of moths had developed and their eggs were in 

 an advanced condition of development and many had already hatched. 

 September 10 larvae of this, the fourth generation, were of various 

 sizes, from quite small to full-grown, but no pupse could be found. 

 The leaves, although practically covered with the mines on their 

 upper surfaces, were still hanging on the trees, and there was but 

 little evidence of serious injury having been done. By October 30 

 quite 50 per cent of the foliage was on the ground and those leaves 

 remaining on the trees were more or less rolled in from the edges. 

 This premature falling of the foliage was undoubtedly due to the 

 work of the leaf -miner, and this seems to haA^e been its principal 

 injury. At this time the larvae were full-grown and had lined their 

 mines with a dense lining of silvery-white silk preparatory to hiber- 

 nation. Leaves picked from the ground contained from 6 to 15 

 larvae per leaf. Leaves examined December G showed no change of 

 condition, no pupa> whatever being found, and this condition w-as also 

 found to obtain on January 21. March 12 a quantity of leaves were 

 collected from the ground, and at this time fully 90 per cent of the 

 larvae had transformed to pupa?, though this stage had but recently 

 been entered, as indicated by the bright-green color. On April 22, 

 at which time the foliage of the apple was just pushing out, only 

 pU'pae could be found, and some of these were quite dark in color, the 

 inclosed moth evidently being nearly developed and ready to escape. 

 The formation of pupae as just mentioned is perhaps to be regarded 

 as abnormally early, since the weather about this time was unusually 

 w-arm. This belief is strengthened by the fact that in infested apple 

 leaves kept in a breeding cage out of doors in the insectary yard the 

 insects were all in the larval condition, except one pupa, on April 

 5, the moths mostly emerging the latter part of that month. By May 

 7 eggs were very abundant on the foliage of the apple tree under 

 observation, as many as 12 being counted on a single leaf, but on 

 some leaves none at all were to be seen. At this date no larvae had yet 

 hatched, though many eggs were in an advanced stage of development, 

 the embryo being readily seen within the delicate shell when examined 

 with a hand lens. By June 24 larvae from these eggs had mostly 

 nuitured and had entered the pupal stage, though a few full-grown 

 larva^ were still to be foimd. The time of nuituring of the first 

 generation in 1906, therefore, agrees closely with this period in 1905. 

 Length of life cycle. — ^Eggs deposited during the night of July 31 

 were very generally hatching on the morning of August 8. The 

 larva leaves the egg by eating directly through the lower surface at 

 one end into the leaf beneath, at once beginning its mine, and is thus 



