53 



considered by some authors as but a variety of Phorodon h inn ////. simply, 

 as it appears, on account of its occurrence; on plum in company with 

 humuli and on account of the general similarity in color and mark; 



During 188G and 1887, its life history was carefully Btndied by the 

 writer, and its identity with the species described under this name 

 Fonscolombe, Koch, and Passerini affirmed. That considerable diffi- 

 culty has been experienced in this task goes without saying. 



FOOD PLANTS OF THE SPECIES COMPARED. 



Notwithstanding the great superficial similarity of the two spec 



the life habits of both during the course of a season are quite dissimi- 

 lar. Whereas Phorodon humuli subsists, as far as known, exclusively 

 upon the different varieties of plum and hop and produces but one 

 return migrating brood in fall, mahaleb, from the time that its migra- 

 tory form leaves the plum, is never found upon the hop, but is able to 

 accommodate itself through succeeding generations to the peculiarities 

 of a considerable number of quite dissimilar plants, which are in no way 

 related to each other nor to the plum or the hop. The diversity of habit 

 of the species after leaving the plum or peach is well illustrated by the 

 fact that its progeny will thrive equally well upon the pear, sunflower, 

 IJiimex, kohlrabi, chrysanthemum, shepherd's purse. Portulaca, and 

 a number of other plants in the conservatory of the Department of 

 Agriculture, among which the following ones appear to be most sub- 

 ject to its attacks: Ehamnus. Mallotus, Rhus, Alfredia, and a 

 cies of tobacco, on most of which plants it multiplies with wonderful 

 rapidity. Considering the great variety of plants which it inhabits, 

 it will not be strange if in the future it shall be found, alter more 

 careful observations, both in this country and Europe, that quite a 

 number of described species are identical with mahaleb) and we believe 

 that we are justified in referring to this species the form described by 

 Mr. Monell under the name of Siplionophora achyrantes 8th Rep. ><»x. 

 and Benef. Ins. 111.. 1879, p. 187). 



Koch's description of mahaleb is quite comprehensive, and can not 

 be mistaken for humuli. If Koch had not seen and examined both 

 species at the same time as found upon the plum, he would certainly 

 not have expressed himself in the words lie used in his description, 

 that, notwithstanding its close resemblance to humuli. it differs mark- 

 edly from that species in the absence of the tooth at the inner apical 

 angle of the first antenna! joint, as well as in other minor characters. 



No one who has studied plant-lice carefully, or who has had occasion to 

 study these twospecies simultaneously, will entertain a doubt as to the 

 correctness of Koch's observation. The characters of the frontal tuber- 

 cles and of the first antenna! joint, which separate the two species, are 

 60 obvious and of such constancy through all generations, except per- 

 haps in the first, that it would at least be hasty to consider them as 

 varieties. There can be no doubt whatever that the two species are 



