CONTRIBUTIONS ON THE CORN ROOT-APHIS. 113 



living lice from the different plants. Armoracea we have found very abundant 

 bere on horse-radish. 



As very complete descriptions of the different forms of Aphis 

 maidi-radicis have been published, no descriptions are given in this 

 paper except that of the winged male, Avhich has not been before ob- 

 served or described. Two of these males appeared in the vials in 

 which Aphis maidi-radicis from the roots of Ambrosia artemisiifolia 

 were being reared on corn, and one in the vial of Aphis from Lep- 

 tochloa filiformis. Two of these were used in experiments ; the other 

 was preserved and is described below. 



Winged $ (fig. 58). — Head, thorax, eyes, and appendages black. Abdomen 

 green, with dark transverse bars on the dorsal side of the 5th, 6th, and 7th 

 somites. The beak reaches the metathorax. The antennae reach the caudal 

 •end of the second abdominal somite. The circular sensoria are arranged on 

 the antennae as follows : 24 on the third, 12 on the fourth, 7 on the fifth, 4 on 

 the sixth. Length of body, 1.50 mm. ; length of wing, 1.75 mm. ; length of cor- 

 nicle, 0.10 mm. (Measurements made from specimen mounted in balsam.) 



In 1856 Doctor Fitch described the corn leaf-aphis (Aphis maidis), 

 and up to 1891, when it was described by Doctor Forbes, what is 

 now known as Aphis maidi-radicis was supposed to be only a root 

 form of that found on the leaves. No one, however, has been able 

 to trace a sexual relationship between the two. Although the sexual 

 forms of A. maidis have never been observed, it does not seem 

 possible that such a relationship as was previously supposed can 

 really exist. Besides, while, as shown by map on page 114, Aphis 

 maidi-radicis is confined to the country east of the one hundredth 

 meridian, Aphis maidis occurs from Maine to southern California. 



THE ERIGERON ROOT- APHIS. 



(Aphiii middletoni Thos.) 



The species Aphis middletoni Thos. is considered here because it 

 has usually been identified as Aphis maidi-radicis in publications ; and 

 because it is impossible to study one of these forms on various food 

 plants over a wide extent of country without studying the other. 



So far as is now known Aphis middletoni infests normally plants 

 of the genera Aster and Erigeron, usually in very large colonies at 

 the crown of the plant just below the surface of the ground or on the 

 large roots. The only cultivated plants it has been known to attack 

 are Cosmos bipinnatus and the China or German asters (Callistephus 

 hortensis), and possibly also dahlias and French artichoke (Cynara 

 scolymus) . 



Aphis middletoni was first described by Cyrus Thomas, in 1879, in 

 the Eighth Eeport of the State Entomologist of Illinois. Since then 

 it has been referred to in literature only in food-plant lists. It has 



