334 CONNECTICUT EXPERIMENT STATION REPORT, 1900. 



A further mutilation, less extensive than those just named, 

 but very evident in some places, is the chafing of the bark 

 by electric light or trolley feed wires. In some cases the bark 

 has been wholly destroyed on one side and the limb killed. 

 And lastly, each year some trees or parts of trees are broken 

 off by severe gales, the injury usually occurring to trees which 

 are not in a very thrifty condition. 



5. Poisoning by Illuminating Gas. 



Illuminating gas is extremely poisonous as well to the roots 

 as to the leaves of trees. A considerable leak from a gas 

 main, under repair, during a single night has killed trees stand- 

 ing near, and a very slight leak for a longer time will also 

 infallibly kill them. 



Many trees have been killed by this cause, the damage often 

 being done before the leak was discovered. 



6. Insect Injuries. 



The insects which commonly injure street trees in New 

 Haven may be grouped as (a) leaf-eating insects, (b) sucking 

 insects, and (c) borers. 



(a) Leaf-eating Insects. 



Elm Leaf-Beetle. Galerucella luteola, Mull. The adults 

 appear in the first half of May, when the leaves are unfolding, 

 and perforate them with small round holes. The females lay 

 their yellow eggs on the under sides of the leaves in irregular 

 clusters. Each female is said to deposit about six hundred 

 eggs, and the egg-laying period extends over several weeks. 

 The eggs hatch in about a week and the young larvae or grubs 

 feed upon the under surface of the leaves, eating off the green 

 portion and leaving only the skeleton covered with the upper 

 epidermis. Such leaves soon turn brown and fall. 



The English elm suffers greater injury than our American 

 species. 



The larvae or grubs do much more damage than the adults, 

 and in from fifteen to twenty days, when full grown, descend 

 the body of the tree or drop from the branches in search of a 

 place to pupate. Large numbers transform at the base of the 

 tree, where, partially covered with fallen leaves or rubbish, they 



