86 . FIFTH ANNUAL REPORT 



are inadequate to account for the wide dissemination of the species. 

 It is very clear to me, however, that by aid of winds and their natural 

 powers of locomotion, the lice can soon overrun a large orchard from 

 a given point; and their wide distribution is easily accounted for hy 

 the transport of the female scales on scions and nursery stock, to say 

 nothing of the aid they get from birds, flying insects and even running 

 water; for Dr. Shinier has shown that this last may, under favorable 

 circumstances, serve as a means of transportation. Moreover, severe 

 storms, passing over infested districts at the right season, may help to 

 carry them still greater distances.* 



FOOD PLANTS. 



Besides the Currant, Plum, Pear, Crab and Persian Lilac, f there 

 is evidence, as we see from Mr. Hanan's letter, that it will also live on 

 the Cherry and Apricot, while the same, or a closely allied species, 

 occurs on the Elm and Sweet Gum in Mississippi, according to Mr. 

 Merchant; on the Mountain Ash, according to Dr. Shinier (Trans. Ills. 

 State Hort. Soc, 1868, p. 228) and others ; on the Dogwood (Am. Ent. 

 II, p. 334), and on the Ash-leaved Spirea, according to Judge J. G. 

 Knapp, in a paper read before the Madison (Wise.) Horticultural 

 Society, at its meeting in 1870. In Europe, what has been taken for 

 the same species, is also found on the Dogwood, as well as on the Elm, 

 White Thorn, Medlar and Currant.J 



The rule among the bark-lice seems to be that each species is re- 

 stricted to plants of a given family, and future investigations may 

 show that those existing on trees, which do not belong to the family 

 RosacecG^ have structural differences, and are distinct, notwithstanding 

 their superficial resemblance. Such differences may be expected, as 

 will be shown in the closing bibliological remarks. However this 

 may turn out, it is very certain that the species in question, though 

 partial above all things to the Apple, yet shows a preference for some 

 of its many varieties, or at least thrives better on some than on others. 

 Dr. LeBaron mentions the Red Romanite, lied Astrachan, Ranibo, 

 Early Harvest, Summer Rose, as being most largely infested, and the 



* After a thunder storm in the midiUe of March, I saw the ground in places in St. Louis sufficiently 

 covered with pollen to appear as though sprinkled with sulphur; and this pollen, upon examination, 

 l^roved by its trilobed and oily character, to belong to some pine, and probably to the Long-leaved 

 pine, which was at that time in bloom in the Southern States, and from which it must have been car- 

 ried a distance of at least four hundred miles. This pollen grain is, though aided in lloating by the 

 lobes, heavier than the young bark-louse; and numerous other instances of thecarryingpower of severe 

 storms are on record . 



t The negative evidence is very strong that the species found on the Persian Lilac is distinct, for 

 some of these shrubs, belonging to Mr. F. Starr, of Alton, Ills., are ci'owded with the scales, in the im- 

 mediate vicinity of apple trees that have none. Yet trom specimens of these scale-covered lilacs, re- 

 ceived from Mr. Starr, and from others examined in other quarters, I can find no superficial dillerences 

 which would enable me to distinguish the bark-lice thereon from the apple-tree species. 



J Boisduval's £rt<omoio£ris Horticole, 318; Taschenberg's Entomologie fuer Gartner and Garten- 

 freunde, 430. 



