86 NEW YORK STATE MUSEUM 



are potent factors in increasing the destructiveness of aphids. 

 One of the best known is the case of the corn root aphid^ and 

 the corn field ant.- This ant colonizes the aphid in cultivated 

 fields, on the roots of weeds and corn, and materially increases 

 its destructiveness. The casual nature of this relationship is 

 exhibited by the observations in Louisiana, of Prof. Wilmon 

 Newell on the recently introduced Argentine ant, I r i d o m y r - 

 m e X h u m i 1 i s Mayr. and native plant lice which are colon- 

 ized by this species and, as a consequence, the latter are decidedly 

 more- injurious in sections where the Argentine ant is abundant. 



Natural enemies 



The almost helpless plant lice are subject to attack by a 

 number of insect enemies. The beneficial ladybeetles or lady- 

 bugs, easily recognized, as a rule, by their red color and con- 

 spicuous black dots, are among the most serviceable of these 

 natural enemies. They, in association with their ugly, black 

 grubs, are frequently found on badly infested trees, feeding 

 voraciously and destroying hordes of these pests. The 2-spot- 

 ted ladybeetle-'^ is one of the more common of these foirms, 

 though the ocellate or 15-spC'tted lad3'beetle* is frequently 

 found in numbers, especially on shade trees. Another com- 

 mon form is the 9-spotted ladybeetle.""^ 



The important part played by the delicate, handsome flower 

 or syrphid flies, should not be overlooked. These insects are 

 usually brightly marked with yellowish and brown, generally 

 with conspicuous, reddish eyes and may frequently be seen 

 hovering in bright sunlight. They deposit their delicately 

 sculptured eggs in colonies of the plant lice, and the greenish 

 or yellowish, sometimes red marked, varicolored maggots, less 

 than half an inch long, devour hosts of aphids before they at- 

 tain maturity. These active enemies of plant lice are easily 

 distinguished from all other species found in such situations, 

 by the body gradually enlarging from the head backwards. 

 The maggots seize individual plant lice, raise them from the 

 leaf and quickly drain the body of its vital fluids. 



^Aphis maidiradicis Forbes. 

 ^Lasius niger americanus. 

 ^Adalia bipunctata Linn. 

 *Anatis ocellata Linn. 

 "Coccinella novem-notata Hbst. 



