Vol. LI I. LONDON. JANUARY. 1920. No. 1 



POPULAR AND PRACTICAL ENTOMOLOGY. 

 The Cottonwood Leaf mining Beetles in Southern Alberta. 



by e. h. strickland, 



Entomological Branch, Dominion Dept. of Agriculture. 



Cottonwoods and other poplars have proved to be the trees best adapted 

 for shade and ornamental purposes on the treeless plains of Southern Alberta 

 and Saskatchewan. It is, therefore, to be regretted that every year the leaves 

 of these beautiful trees are made unsightly by the presence of large blackened 

 areas, which may extend over their entire surface. In some years hardly a leaf 

 on badly attacked trees escapes this disfigurement. 



By the middle of June an examination of the cottonwood trees around 

 Lethbridge, Alberta, can hardly fail to reveal the presence of small groups of 

 holes on the underside of the leaves, (Fig. 2) with perhaps a few^ smaller groups 

 on the upper side also (Fig. 1, A). 



A closer examination of these holes shows that they are never more than 

 about 1 mm. in diameter and are polygonal in shape, being bounded by the 

 finer reticulations of the leaf veins. They do not entirely pierce the leaf but 

 extend to the upper epidermis, which appears as a transparent membrane 

 when the leaf is held to the light. After a few weeks they become more circular 

 in outline, and are surrounded with a cork-like growth. 



These holes are the feeding punctures of the Cottonwood and the Poplar- 

 leaf-mining beetles (Zeugophora sciitellaris Suffr. and Z. abnormis Lee). 



The former beetle, which we shall consider more especially in this article, 

 is a pretty little species, measuring 4 mm. long, with a bright yellow thorax 

 and with black wing covers. (Fig. 3). This beetle feeds most abundantly 

 on cottonwoods, though it is found sparingly on other poplars. 



Weiss and Nicolay* in recording the occurrence of this beetle in New 

 Jersey, where they state that it appeared first in 1919, describe it as a " European 

 Poplar Leaf-miner." We are inclined to doubt whether this species has been 

 imported from Europe. Mr. Criddle tells me that, from the earliest dates upon 

 which he made observations on the cottonwood- infesting insects of Manitoba 

 this beetle has been abundant, especially upon the native cottonwoods in river 

 bottoms. This observation was made in 1903, when very few cottonwoods 

 had been imported into Manitoba from elsewhere, and Mr. Criddle has noticed 

 that the beetles do not spread rapidly to the imported trees. In Alberta our 

 first personal record was made in 1913, but the inhabitants of Lethbridge in- 

 formed us at the time that, in so far as they had observed, the cottonwood 

 leaves were always more or less disfigured with black blisters. 



Zeugophora abnormis is a beetle similar in size to Z. srulellaris, but it is 

 entirely black. It is rarely seen on cottouAvoods, but it confines its attention 

 chiefly to Balms of Gilead. 



*Ento. News, vol. 30, May, 1919. ' 



