THE YELLOW CLOVER APHIS. 39 



wliich had not proviousl}^ laid eggs were used, while in the earlier 

 counts no choice was made, which probably accounts for the differ- 

 ences in the average. Similar egg counts for Macrosvphum pisi show 

 it to be much more prolific in Qgg production; in fact the counts for 

 pisi were nearly twice those for irifolii. 



Although we find both species attacking red clover, the one (pisi) 

 is often quite abundant and destructive to clover, while the other 

 (trifolii) is seldom if ever injurious. One of the principal causes of 

 this difference will be readily understood from what has just been 

 noted, namely, the great difference in fecundity of both viviparous 

 and oviparous females. Other habits which doubtless have an influ- 

 ence in making trifolii less abundant are its sporadic mode of living, 

 the comparatively late date of hatdiing from the egg, and the addi- 

 tional fact that it always winters in the egg stage while in jnsi the 

 eggs liatch earlier in spring and many individuals winter as viviparous 

 females, thus giving it the advantage of an early start. Further, pisi 

 has a variety of hosts, which is not ti-ue of trifolii in America; and, 

 finally, the latter species requires a nuich smaller c(uantity of sap for 

 becoming mature than does pisi, and as a result it is individually less 

 harmful to the plant. 



NATURAL ENEMIES. 



Doubtless the most important checks on the yellow clover aphis 

 are the weather conditions, more especially heavy rains. The aphis 

 fungus, Empusa apliidis, is Hkewise (juite an important factor in hold- 

 ing this plant-louse in check. 



On account of its habits of living singly and jumping from the leaf 

 at the least disturbance, this species is seldom attacked by internal 

 ])arasites. Mr. Paul Ilayhurst noticed a few parasitized specimens 

 of this species at Chevy Chase Lake, Md., July 9, 1907, but appar- 

 ently no parasites issued. The writer has likewise found occasional 

 specimens parasitized, but has never reared the parasites. 



Of the coccinellids, three species, Megilla maculata DeG., Hippo- 

 damia converqens Guer., and Coccinella 9-notata Herbst, were reared 

 to the adult stag(> in the insectary at Washington, from larvae wliich 

 were feeding on Callipterus trifolii on material received from Cadet, 

 Mo., June 19, 1889. 



The writer observed the 9-spotted ladybird (CoccineUa 9-notaUi 

 lle>rbst) attacking the yellow clover a])his at l^rbana, lU., Septem- 

 ber IS, 1913, and larvae of what were considered the same species 

 were not uncommon on th<> badly inf(>ste(l clover ])hints, devouring 

 the ajihides. 



At La Fayette, Ind., we have reared a species of Aphiiloletes from 

 larva' feeding on this aphis in chimney cages, although it has never 

 been found attackmg it in the field. 



