38 LEAF-MIXING INSECTS 



capacity of the leaves. Our maple sugar crop is con- 

 siderably reduced each year by the operations of the little 

 leaf -mining casebearer, Paraclemsia acerifoliella (see p. 78). 

 Very unsightly foliage effects are produced by a good many 

 leaf-miners on trees, notably by Gracilaria syringella on 

 lilac, by Chalepus dorsalis on locust (Chittenden, Hutchings, 

 1924), by Zeugophora scutellaris on poplars, and by several 

 imported sawfly miners on elm, alders and birches ; also, in 

 coniferous trees by Argyresthria thuiella, in arborvitae 

 (Britton, 1922) by Recurvaria piceaella on spruce (Gillette, 

 1922) and by ^oleophora laricella on tamaracks (Herrick, 

 1912) . There is hardly a meeting of economic entomologists 

 held anywhere but that receives reports of injurious abun- 

 dance of leaf-miners in field, garden or orchard crops. 



Control methods for leaf -mining insects are only beginning 

 to be well worked out. Arsenical poisons are, of course, un- 

 availing (unless to adults) since they cannot be applied to the 

 food of the larvae, covered as it is completely by the epi- 

 dermis of the leaf ; but good results are obtained by the use 

 of rather strong outdoor applications of nicotine sulfate, oils, 

 and other contact insecticides; also by fumigants, when the 

 plants may be inclosed for treatment, as in a green house. 



HOST PLANTS 



Our list of plants, in Chapter XVI will give specific 

 information as to where leaf -miners have been found. It is 

 a long list and it includes nearly all the more familiar seed 

 plants. These range in character from succulent purslanes 

 and thin grasses to stately trees. In general it may be said 

 that leaf-miners prefer the better constructed, and longer 

 enduring leaves of woody plants. 



The groups of plants sought by the most species are the 

 Amentiferae, especially the willows, poplars, birches and oaks 

 (the oaks before all) and the rose family. The maples, 

 legumes and composites have a fair proportion. A few are 





