94 TEANSACTIONS OF THE ILLINOIS 



important problem be disposed of, and this is why I call your atten- 

 tion to the matter now. The history as far as known is this: The 

 species winters on the apple tree either at the base of the buds, or 

 even between their scales, in cracks of the bark and similar situa- 

 tions, and hatches in early spring even before the leaves unfold, and 

 the young lice may often be seen upon the unopened bud as if wait- 

 ing for the leaves to expand. These young infest the foliage, con- 

 sequently, from the beginning, taking it leaf by leaf as it is exposed 

 to their attack. All of this generation are females and multiply 

 rapidly, bringing forth living young which in turn rapidly mature 

 and devolop other generations. Then a winged brood appears, 

 which, late in June and early in July, deserts the apple and goes — 

 we know not where. And then nothing more of these lice is known 

 until September, when they again appear upon the apple, — a single 

 winged female here and there upon a leaf. This returning brood 

 brings forth the final generation of the year — now both males and 

 females — and there give origin to the eggs which carry the species 

 through the winter. 



The positive facts here given have long been known, both in 

 this country and the old world, but this midsummer absence from 

 the apple seems to have been first noticed in Germany by Dr. Kes- 

 sler. Our own notes upon the species — principally made this year 

 by Mr. Weed — confirm Kessler's statements most precisely, but 

 throw no light whatever upon the history of the species during the 

 two midsummer months. From the known facts concerning other 

 plant lice related to this of the apple, in whose seasonal history a sim- 

 ilar hiatus occurs, it is practically certain that our aphis migrates at 

 this time to some other plant, breeding there for a generation or two 

 in July and August, and that from this plant, whatever it may be, the 

 last brood returns to the apple in fall as described above. The only 

 clue we have to the food plant of this species alternating with the 

 apple is a theoretical one. It is altogether probable that this aphis 

 deserts the apple after the leaves have made their principal growth, 

 for the purpose of satisfying its voracious appetite and maintaining 

 its inordinate rate of increase upon some plant which puts forth 

 foliage more vigorously later in the season, its final return to the 

 apple in fall being clearly only for the purpose of placing its young 

 in position to avail themselves of the early leafage of that tree. 

 Will not you horticulturists do this joint service to horticulture 

 and to entomology; viz: first, to notify me, to observe carefully the 

 apple-louse in spring until you are sure that you know it, and then 

 when it disappears in June or July from your apple trees, watch for 

 the subsequent extraordinary development of a similar plant-louse 

 on other vegetation? And when you think you have a clue, will 

 you not take the further trouble to send us many living specimens 

 for comparison and for experimental use? For here is a point in 

 which the horticulturist is dependent upon the entomologist. They 



