12 



LIFE HISTORY OF THE ALDER BLIGHT APHIS. 



With them were also a few small colonies of larvae which had settled 

 on the branch, while recently deposited larvae were also observed on 

 the leaves. 



June 7, 1901^. — Received to-day from Chatham, Va., some leaves of 

 maple infested with pupa? and migrants of PenfhpMgus acerifolii. A 

 number of these migrants were placed with a potted plant of alder 

 for observation, and I found the following day that quite a number 

 of these migrants had settled on the underside of some of the leaves, 

 and with them were many young larvae which they had deposited, 

 all of which proved them to be identical in every respect with those 



oiPerrhphigus tessellata. These 

 larvae were reddish or brown- 

 ish red and provided at the 

 anal end of the body with a 

 white and curly or cottony 

 secretion, which gradually 

 spread over the whole insect 

 until it had the appearance of 

 a little lump of cotton. 



Migrants which were placed 

 with a potted maple died with- 

 out depositing any larvae. 



June 23, 7^5.— Observed 

 to-day some migrants of Pem- 

 phigus acenfoUi, on the un- 

 derside of leaves of alders, 

 Alnus rugosa, near the Chain 

 Bridge, District of Columbia. 

 They were each surrounded by 

 a circle of about 28 larvae, all 

 of which had already cast 

 their first skin, which was ad- 

 hering to the leaves. These 

 larvae were orange and their 

 abdomen covered with a long 

 and backward-directed, cottony secretion, whereas that of the thorax 

 was shorter and quite erect, longest along the median line. Some- 

 times three or four of the migrants had settled on the same leaf; 

 some of them were already dead or barely living. On some of the 

 leaves were several rings of cast skins, varying from 18 to 40 in num- 

 ber, while on the branches of the same shrubs were numerous larger 

 or smaller colonies of larvae. 



April 11, 1905. — \Vhile examining trunks of maples near Rosslyn, 

 Va., I found, under the shaggy bark of a tree, numbers of dead and 

 dry return migrants, and with them also some of the young stem- 



FiG. 1. — ProcipMlus tessellata: Migrants 

 from maple to alder. (Original.) 



