The Plum Leaf-miner ■ 225 



Mine. — When newly hatched, the larva commences a long and ex- 

 tremely slender mine, which, being filled with blackish excrement, appears 

 almost as a crooked black line; but, after continuing in this linear track 

 for some distance, the larva mines a complete blotch of an irregular oval 

 figure, and of a pale greenish white color; in the central portion of this 

 blotch the black excrement forms a little heap; not unfrequently two 

 larvae, mining in the same leaf, will meet at the blotch portion of the 

 mine, and have a larger blotch in common. The larva leaves its mine 

 to spin its cocoon. 



Larva. — Length 2 lines. Pale amber, shining, transparent, dorsal 

 vessel slightly greener; head small, reddish brown, working up under the 

 prothorax, through the upper surface of which the posterior part can be 

 distinctly seen. 



Cocoon. — The cocoons average 3 mm. in length and 1.75 mm. in width, 

 forming a long oblong oval. There is a wide flange around the three sides 

 of the cocoon, one of the long sides being almost devoid of it, however. 

 This side rises directly to the highest point of the domed surface which sur- 

 mounts the flange, the elevation being more gradual on the other side. 

 The domed area is comparatively smooth, with a few fine, slender, irregular 

 reticulations, rather darker than the ground color; the latter is ochreous 

 brown, inclined to yellowish. There is a considerable amount of loose 

 flossy silk of the same color as the silk of the cocoon scattered over the 

 flange, a similar, but much thinner, coating covering the domed surface. 



There are two broods, the adults appearing in May, June, and August, 

 the larvae of these feeding respectively in September-October and July- 

 August. 



MEANS OF CONTROL 



The plum leaf -miner has proved to be a difficult insect to control, owing 

 to the fact that from the time the larva leaves the egg it feeds entirely 

 within the leaf out of reach of any poison spray. Measures directed against 

 the moths, eggs, and larvae have all proved failures, and only partial 

 success has been attained by thorough cultivation to destroy the larvae 

 and pupae in their cocoons. 



Attempts to kill the moths. — As the moths rest during the day in great 

 numbers on the bark of the trunk and larger branches, it seemed feasible 

 at first to kill them with a contact spray. At the suggestion of Professor 

 Slingerland, Mr. Hooker tested this method in May and June, 1909, 

 using whale-oil soap, 30 pounds in 150 gallons of water. He did this work 

 very thoroughly, using two double nozzles and spraying from two sides 

 of the tree at the same time. While many moths were killed, many more 

 escaped and the infestation on these trees was as bad as in previous years. 

 The dead moths were to be seen still sticking to the bark late in the summer. 



