Dec., '07] ENTOMOLOGICAL NEWS. 431 



An undescribed Dimorph of the Box Elder Aphid 

 Chaitophorus negundinis. 



BY L. C. BRAGG, Colorado Agricultural College. 



(Plate XVII. i 



The alatc and apterous forms of the above Aphid were de- 

 scribed by Professor Cyrus Thomas, in 1878, in Illinois. 



On June I9th, 1905, the writer found the climorph in Fort 

 Collins, Colorado, on the upper veins of the leaves of the box 

 elder, Rolac ncgnndo. This form was so exceptional with the 

 twenty-two leaf-like flabellse arranged on the margin of the 

 abdomen that the resemblance to the European species, Ch. 

 accris, which has fourteen, was very striking. 



This form was kept under observation during the summer, 

 and the facts demonstrated that it does not moult and does 

 not reproduce. Many empty skins were found where the aphid 

 had been sucked dry by some predacious insect, but none 

 showed the characteristic split on the back that one finds in all 

 moulted skins. 



In 1906, I began early to look for the dimorph, but did not 

 mid it until June 4th. They did not become plentiful until 

 the middle of the month, and I could not determine whether 

 they were the progeny of the alate or of the apterous form. 

 On June i6th, I began dissecting the mature insects, and soon 

 learned that both the apterous and alate forms gave birth to 

 the dimorph. Not only this, the dimorph was associated with 

 the normal young in the same mother in several instances. 

 Of one hundred specimens dissected, there were nineteen alate 

 females and eighty one apterous females. Of the nineteen 

 alate specimens, fourteen had dimorphic embryos only, while 

 five had the normal forms only. Of the eighty-one apterous 

 females, thirty-nine contained dimorphic embryos, and forty 

 the normal form. These results would indicate that the di- 

 morphic form is produced in as great numbers as the normal 

 form in this generation. The leaves of the host plant would 

 also indicate this, for they sometimes crowd each other on the 

 veining of the upper side of the leaf. The normal form sucks 

 the under side of the leaf and the tender stems. It would 



