130 Annals Entomological Society of America [Vol. I, 



cutting of the grain are driven into the outlying standing patches. 

 There certainly was no protection received from their gregarious 

 sleeping, since the groups of wasps were very conspicuous 

 objects in the failing light. 



Perhaps it would require considerable knowledge of wasp psy- 

 chology, to be able to answer, first, why they congregate at all, 

 instead of each sleeping on whatever stem of oats happens to be 

 convenient, and second, why when thus congregating they ignore 

 the similarly situated groups of other, even close related species, 

 and choose only those of their own fellow^s. The wide range of 

 the species implicated would seem to indicate that the habit 

 is either a fundamental one, or else a general response to some 

 peculiar environmental condition. 



Entomological Laboratory, The Uni^•crsity of California, August 1, 1907. 



NOTES ON THE LIFE HISTORY OF THE LEAFY DIMORPH 

 OF THE BOX-ELDER APHID, CHAITOPHORUS NEGUN- 



DINIS THOS.* 



By J. J. Davis, Office of the State Entomologist, Urbana, III. 



My attention was first called to this curious dimorph by Mr. 

 J. T. Monell, who found it at St. Louis, June 21, 1907, and had 

 received it from Oestlund as early as 18S9. 



The life history of the dimorph I have found to be essentially 

 like that of the dimorph of the European C. testudinatus Thorn., 

 as described by Kessler. 



In central Illinois the viviparous females begin to produce 

 the dimorphs about June i, and the latter, after crawling over 

 the leaves for a short time, attach themselves to the veins of 

 either surface of the leaf. There they remain in a dormant con- 

 dition for two or three months. By the last of June or the first 

 of July the parent females begin to disappear, and soon only strag- 

 glers can be found. In the latter part of August the dimorphs 

 revive, molt several times, and become viviparous females. Sub- 

 sequent generations are oviparous, and lay the eggs which are to 

 carry the species over the winter. 



The dimorphs are inconspicuous; they appear as minute flat 

 scales lying close against the leaf, and having the same green color 

 as the leaf. 



