522 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



confined to certain trees, and mainly so to tlie White Poplar and tlie 

 Cotton-wood. Along the Baltimore and Potomac Railroad tracks 

 these trees were defoliated as far as five miles from the Capitol. In 

 Georgetown the caterpillars were equally noxious, but in the adjoin- 

 ing forests but very few webs could be seen. 



The j)roportionate injury to any given species of tree is to some 

 extent a matter of chance; and in some resj)ects a year of great injury, 

 as 1886, is not a good year to study the preferences of a species, be- 

 cause when hard pressed for food the caterpillars will feed upon al- 

 most any plant, though it is questionable whether they can mature 

 and transform on those which they take to only under the influence 

 of such absolute necessity. Again, the preference shown for partic- 

 ular trees is more the result of the preference of the parent moth than 

 of its progeny in a case of so general a feeder as the Fall Web-worm. 

 We had a very good illustration of this in Atlantic City last autumn. 

 The caterpillars were exceedingly abundant during autumn along this 

 portion of the Atlantic coast, especially on the trees above named. 

 We studied particularly their ways upon one tree that was totally de- 

 foliated by September 11. The bulk of the caterpillars were then just 

 through their last molt, though others were of all ages, illustrating 

 different hatchings. There was an instinctive migration of these 

 larvse of all sizes, and the strength of their food-habit once acquired 

 from birth upon a particular tree was well illustrated. At first the 

 worms passed over various adjacent plants, like Honeysuckles, Roses, 

 &c., the leaves of which they freely devour if hatched upon them; 

 but as the migrating swarm became pressed with hunger they finally 

 fell upon these, and even upon plants like the Peach and Ailanthus, 

 which ordinarily are passed over. They would even pounce upon 

 any food, and a rotten apple placed in their way was soon literally 

 swarming with them and sucked dry. 



In a general way it may be stated that conifers, grapes, and most 

 herbaceous plants are free from their attacks, and it is very doubtful 

 whether the species can mature upon them. 



The list of plants which follows is arranged according to the rela- 

 tive damage to the foliage in the city of Washington. The three 

 first named are most subject to attack, and in fact are almost always 

 defoliated. 



PROPORTIONATE INJURY TO DIFFERENT PLANTS AND SHADE TREES. 



The damage done in the city of Washington was exceptional, but 

 so was also the general damage throughout the New England States, 

 if not throughout the country. In New England the greater predi- 

 lection which the species showed for Poplar, Cottonwood, and the 

 ranker growing Willows was everywhere manifest, and so much was 

 this the case, that the destruction of the first brood on these trees 

 would have substantially lessened the damage to other trees. 



Plants marked 1 have lost from 75 to 100 per cent, of their foliage. 



Plants marked 2 have lost from 50 to 75 per cent, of their foliage. 



Plants marked 3 have lost from 25 to 50 per cent, of their foliage. 



Plants marked 4 have lost from 1 to 35 per cent, of their foliage. 



Plants marked with two figures have shown the relative immunity 

 or injury indicated by both, the variation being in individual trees. 

 1. Negundo aceroides Moench. (Box Elder.) 

 1. Populus alba L. (European White Poplar.) 

 1. Populus monilifera Ait. (Cottonwood.) 



