14 OUR SHADE TREES AND THEIR INSECT DEFOLIATORS. 

 MORE RECENT EXPERIENCE AT THE DEPARTMENT. 



The more recent experience in the destruction of this Galeruca on the 

 Department grounds may now be summed up, the experiments having 

 been intrusted to Dr. Barnard. 



Past History of the Elms in question. — According to Mr. William Saund- 

 ers, of this Department, these trees have been annually attacked by the 

 European Elm Leaf-beetle since they were planted ten years ago, and 

 about one year in three the injury has been severe, resulting in their 

 defoliation, while in other years, as in 1879 and 1880, there appeared 

 comparatively none. In some seasons a second or autumnal set of leaves 

 appeared after the trees had been stripped, and in certain of these in- 

 stances the second crop of leaves became eaten ; but in all cases he 

 thinks the lives of the trees have not seemed to be endangered and they 

 soon repaired the damage done. His belief is also that the pest did not 

 become gradually worse and worse through the series of years during 

 which it has been observed by him, still he regards the attack of 1882 

 as worse than any known to him before on these trees or others, and 

 he has noticed the effects of this insect since 1S50, first in its earliest 

 ravages about Baltimore, and later elsewhere. 



Condition and Characteristics of the Grove in 1882 and 1883. — However 

 it may be for the past history or future desirability of certain trees in 

 the grove, in 1882 many exhibited various grades of feebleness, and some 

 had dying branches. Indeed, a few of them had a very unhealthy as- 

 pect the previous year also. Of course it can be claimed that their 

 unhealthy condition is due to other causes than the insects ; and it should 

 be remembered that most are foreigu species, each often represented in 

 two or more of its varieties. Here all grow on level ground, whereas 

 in a state of nature some belong to mountainous localities ; others to 

 the damp climate of England, &c. Therefore, many of them are grow- 

 ing under abnormal conditions. They exhibit much variety in the 

 relative abundance, size, form, and texture of the leaves. There is also 

 great diversity in the density and form of branching. 



Extent of Injury in 1882 and 1883. — All the varieties and species of 

 elms in this grove, without exceptiou, were preyed upon by the pest in 

 1882 and 1883. The insect, however, showed decided preferences for 

 certain individual trees, varieties, or species, stripping some completely 

 before doing more than very slight harm to the leaves of others, the 

 former becoming completely eaten in midsummer, the latter not until 

 toward the close of the season, or remaining only slightly damaged 

 until then. In 1882 the leaves were eaten faster than they could be de- 

 veloped, and the insect continued abundant enough to prevent a second 

 crop of foliage until in November, when it became too cold for the 

 leaves and active insects to exist. 



On these grounds the southeast half of each tree has suffered more 

 than the northwest half. This peculiarity has been very strongly pro- 

 nounced this year, 1883, on all the trees affected, and upon some exam- 



