294 Jotnmal of Agricultural Research voi. vi, No. s 



FOOD PLANTS OF THE LEAF MINER 



This leaf miner is primarily a pest of the foliage of the apple. There 

 is where it abounds. However, the small caterpillars have been found 

 developing in considerable numbers in the leaves of the crab-apple (Malus 

 sp.), and to a less extent in the leaves of the haw (Crataegus spp.), plum 

 {Primus spp.), cherry (Prtmus spp.), and pear {Pyrus spp.). In the case 

 of the last four trees only an occasional mine has been observed. Cham- 

 bers (2) and others have also reared it from mines in the leaves of the 

 wild cherry {Prunus spp.). 



CONTROL OF THE LEAF MINER 



While this miner may develop in such numbers that from 90 to 95 per 

 cent of all leaves on apple trees may contain from i to 10 or 15 mines, it 

 must be said that it is not an especially alarming pest of the orchard 

 (PI. XXXIII, fig. 14, 15). The pest increases in abundance as the 

 summer and fall advance, so that by September or October much of the 

 foliage may be consumed, but by that time the tree has about completed 

 its growth and matured its crop. However, when conditions are favor- 

 able and the pest is abundant, steps should be taken to prevent it from 

 reappearing in injurious numbers the next season. 



Since the caterpillar enters the leaf immediately on hatching and 

 remains in the mine until mature and ready to spin its cocoon for pupat- 

 ing, arsenical and contact sprays are of no value. Applications of 

 sprays have given the writer absolutely no results. From the general 

 nature of the pest and its habits, there seems to be no feasible means of 

 controlHng it during the growing season. Since it passes the winter 

 as the pupa in cocoons on fallen leaves, it can be effectively controlled 

 by destroying the leaves early in the spring. The most practical method 

 of destroying the pupae on the leaves is to use a disk for shallow cultiva- 

 tion before the first of March so as to work under the leaves before the 

 moths begin to emerge. Summer cultivation will not help, since the 

 pest is not found on the ground at that time. In a small home orchard 

 the leaves can be raked together and burned or piled and used for leaf 

 mold. If they are not burned, they should be covered with enough 

 soil or stable manure to hasten the decay of the leaves and prevent the 

 moths from emerging in the spring. 



PARASITES OF THE TENTIFORM LEAF MINER 



It w^ould seem that a caterpillar of this type, which lives protected 

 inside the leaf from the time it hatches from the egg until it is ready to 

 pupate, would be as well protected from natural enemies as from arti- 

 ficial treatment given by man. This does not prove to be the case, 

 however, for the pest is heavily parasitized. It resembles other insect 

 pests which are subject to the attacks of parasites in that under favorable 



