PEAR FLEA-LOUSE, 135 



Dr. Harris gives a short account of the damage produced, probably 

 by the same species, in Massachusetts, between the years 183i and 1838 

 inclusive, and speaks of one individual who lost several hundred pear 

 trees from this cause. No record however has heretofore been made of 

 its appearance in the Western States. 



The following additional particulars in the habits of this insect were 

 subsequently communicated to n»e by Mr. Earle, under date of July 10: 



" I first observed the strange exudation of sap on the leaves of my pear trees about the 

 middle of May, noticing it first upon the Duchess d'Angouleme variety. After a few days the 

 injury seemed to extend to every leaf of every tree of that variety in the orchard, and to a 

 less general extent, involving the Howell, Bartlett, and Lawrence varieties. The sap exuded 

 most seriously from the axils of the leaves, but was found in globules, scattered over the sur- 

 face of most of the leaves, slowly drying away to a sticky sirup. All growth was at once ar- 

 rested, and the trees lost a portion of their leaves, amounting, in some cases, to more than a 

 quarter of the foliage. The extent of their ravages was about as great at the time of your 

 visit, on the first of June, as at any time thereafter. I saw no particular change for a week 

 or so, when we had a heavy rain, after which they appeared less numerous. But whether the 

 little pests were destroyed by the rain, or had just then reached the end of their destructive 

 career, I am not able to say. The whole term of their visible depredations in my orchard 

 was a little less than one month. I find that ray neighbors suffered in the same manner and 

 to about the same extent." 



Many species of insects are found inhabiting the two continents, 

 which are so similar to each other, that they have been denominated 

 representative species. The increased facilities of communication are, 

 every year, bringing new instances of this kind to the knowledge of 

 entomologists, in which insects that have long been supposed to be pe- 

 culiar to one country, are found repeated in the other, with no greater 

 variation than species are known to undergo, in their own country, from 

 a change of food, locality, and other circumstances. Whether these in- 

 sects are really distinct species or modified descendants from a common 

 origin, is one of those obstruse questions in natural history, which, with 

 our present knowledge, we are, in many cases, unable to decide. Bnt 

 where the species in question are known to subsist upon the common 

 fruit trees or vegetables, and where their transportation can be easily 

 explained, the best course would seem to be to assume their identity, 

 unless the differences are important and of a decidedly organic charac- 

 ter. One of these instances is furnished by the little insect now under 

 consideration. From a comparison of the few specimens of the winged 

 insect in my possession, with such descriptions of the European insect 

 as I have access to, I should be led to regard them as different species ; 

 but a colored figure of the Psylla pyri of Europe, by the accurate hand 

 of Mr. Westwood, communicated to me by Mr. Eiley, resembles my 



