320 Forty-sixth Report on the State Museum 



trees which had been set the year before. These trees, in the autumn 

 after they were planted, wore an unhealthy aspect, and had patches of 

 a blackish rust upon their branches. During the second summer, the 

 trees died ; and other trees on which this same rusty matter was found, 

 proved to be infested with the same insects." 



Whether the insect had appeared in the United States prior to this 

 is not definitely known, yet there is reason to believe that it may have 

 been operating in the State of New York as early as in 1824, if not in 

 the preceding century. 



In an article on " Pear-Tree Blight " by Dr. J. J. Thomas, in the 

 Cultivator for June, 1850, vii, p. 204, it is stated that Mr. E. J. Genet 

 had written expressing his belief that the disorder was caused by an 

 insect observed by him, and operating in the following manner: At a 

 little before midsummer, in the absence of dew for several nights, liquid 

 drops could be seen falling from a pear tree, which was subsequently 

 found to proceed from minute aphides thickly covering the shoots or 

 branches, and which had at first escaped notice from the indentity of 

 their color with that of the pear bark. They continued for about ten 

 days, and then disappeared. The varnish which these insects exuded was 

 regarded as poisonous to the tree. 



Mr. Genet states that the same disorder had appeared on the banks 

 of the Hudson in 1780-1793, and in 1802-1807. As these attacks may 

 not have been seen by the waiter, it is not improbable that they were 

 the true "pear blight." "In 1824," Mr. Genet writes (probably from 

 personal observation), "the same disorder prevailed, and lasted four 

 years. In 1846 we were once more suffering from the same cause, and 

 our pear trees are still prostrated by its fatal attacks. This disease has 

 been called by some 'fire-blight.' One w^riter saj^s it is produced by 

 the Aphis lunata, a small insect covered by fine, white wool, but the 

 insect which came under my observation is very different in every char- 

 acteristic — so small as to escape observation in the first stage, and so 

 similar to a fly at maturity as to mislead "an inattentiA^e observer." 



As the insect, from characters given, could not have been the common 

 and well-known apple tree aphis, there can hardly be a doubt of its 

 having been the pear-tree Psylla. Its introduction may easily have 

 occurred as early as 1824, as pear-trees had been imported by nursery- 

 men for thirty years prior to that date.* 



Dr. Harris' attention was first drawn to the Psylla in 1848 by Dr. 

 Plumb, through a communication j^ublished in the American Agricid- 



* See article on " Early Pear Importations" in the Country Gentleman for December 1. 1892 

 page 907, where importation of pear-trees as early as in 1794 is recorded, and of other fruit-trees 

 in the first decade of the present century, which, doubtless, " would easily be the means of 

 mporting such^noxlous insects as infested them/' 



