IOWA ACADEMY OF SCIENCES. 137 



the dissemination of these insects. In the autumn of 1891 many of the 

 leaves fell to the ground and were carried away by the winds before the 

 larvic could issue. Many trees are located on the banks of streams into 

 which the leaves may fall, and in case the larva; has not begun to issue so 

 that the water cannot enter the gall, they may be carried many miles down 

 stream and cast ashore; then the larva? issue, transform to the adult stage, 

 migrate to the proper host and are in condition to multiply during the fol- 

 lowing season. In a number of cases the adults have been found in places 

 quite distant from any hackberry trees. At first thought it might be held 

 that a strong wind caught them while on the wing and carried them away. 

 But this is doubtful, since they may have come from leaves that were carried 

 away. 



NATURAL ENEMIES. 



A number of parasitized larvae were taken about September 1. At differ- 

 ent times small white larva? were found in the cell with and devouring the 

 Psyllid larva. Upon further examination it was found that the cause for 

 some of the Psyllid larvae changing to such a brown color and having such a 

 dry, shriveled appearance was that the egg for this white footless larva had 

 been deposited within the Psyllid larva; others were prol)ably deposited 

 outside the Psyllid larva, and so fed externally. 



This parasite belongs to the family Chalcidida in the order Hymenoptera, 

 and attacks all the species found at Ames, Iowa. 



Specimens of the Psyllida^ were sent to Dr. C. V. Riley, U. S. Entomolo- 

 gist, Washington, D. C, for determination and the following species were 

 named: 



Pachypsylla celtidis-mamina. 



Pachypsylla celtidis-minuta. 



Pdchypsylla celtidis-asteriscus. 



Since then specimens ot Pachypsylla celtidis- gemma have been found, 

 and also a new species that infests the twig of the hackberry. As far as I 

 know, no mention has been made of it, and so liberty will be taken to give 

 the most prominent characters, i. e., those used in determining the species 

 as shown in the table below. 



The following is a table prepared by Dr. C. V. Riley for the classification 

 of the three most common species of the genus Pachypsylla. 



Perhaps many members of the Academy do not have access to this table, 

 and therefore I take liberty to insert it in this article and also add the char- 

 acters for separating the species which infest the twig of the hackberry. 



" Head and dorsum opaque; front wings submembranaceous or subllgatine, not 

 rugose: pterostigma. distinct: both marginal cells very long, narrow, and of 

 about equal size and length ; anal style of full-grown larva and pupa long. 



Dorsulum and mesonotum alutaceous, glabrous; front wings narrowly rounded at 

 tip, widest In basal lialf ; genital segment of female longer than the rest of the 

 abdomen; anal style of full grown and pupa notched at top venunta. 



Dorsulum and mesonotum rugoso-punctate, with distinct but very short, sparse 

 pubescence; front wings broadly rounded at tip, widest in terminal half; genital 

 segment of female sliorter than the rest of the abdomen: anal style of full-grown 

 larva and pupa pointed at tip c.-mamma. 



Head and dorsum shining, without pubescence; front wings somewhat convex, basal 

 half not wider than terminal half, broadly rounded at tip, distinctly rugose. 



