36 PROTECTION OF PLANTS, 1918-19 



brood appeared on June 6, and the second on July 20. In 1918 the first brood 

 appeared on May 21, and the second on July 13. One or two stray flies were 

 observed in late September at work ovipositing. These I took to be a third 

 generation. 



The flies on emerging immediately begin to oviposit, choosing the soft, tender, 

 young leaves in which to insert their eggs, in preference to older and harder 

 foliage. During the warm sunny days there is much activity and the flies are not 

 readily taken, but on cloudy days the insects are dull and easily caught in wide- 

 mouth bottles. I have watched carefully for males but have never observed any 

 sign of mating. 



Egg. — The egg, which is white, round and .3 mm. in diameter, is inserted into 

 the leaf through the upper surface in a slit made by the saw of the fly. Many 

 eggs may be laid on the same leaf by the same fly. These hatch in about 8 days. 



Larva. — The young larvae work at first in very restricted areas, but later due 

 to the joining up with other mines the entire parenchyma of the leaf is eaten out 

 and the upper surface becomes brown and badly blistered. When fully grown 

 they average 7 mm. long and .75 mm. wide, are of a shiny white at the extremities, 

 noticeably segmented, the alimentary canal showing green through the skin. The 

 thoracic legs are brown, ringed and situated somewhat laterally, the prolegs being 

 rudimentary. 



Pupa. — When ready to pupate the larva eats a hole in the ceiling of its prison 

 and drops to the earth where it constructs a small, very dark, oval cocoon about 

 1 inch below the surface of the soil. As the silk is very sticky, sand and small 

 readily adhere to the pupal cases, giving them odd irregular shapes. The pupal 

 transformation requires about three weeks to complete. 



Control. — First as to natural control, I found during the summer of 1917 a 

 species of mite attacking the fly, and from some pupal cases I had caged in the 

 insectary several hymenopterous parasites emerged. 



I have also observed numbers of the flies caught in spider webs in the alders. 

 From observations made in experiments, it is apparent that many adults, from 

 various causes, become imprisoned in their cocoons and never get to the surface of 

 the ground. 



Under artificial measures several contact insecticides have been tried • 

 Kerosene Emulsion, 1 part stock to 5 parts water, was found the best spray 

 This was applied when the larvae were young and their work beginning to be 

 noticed on the leaf surfaces, and killed practically 100 per cent of the larvae. A 

 weaker solution, 1 part stock to 7 parts water, was efi'ective only when applied 

 immediately after the eggs had hatched. 



