THE PEA APHIS WITH RELATION" TO FORAGE CROPS. 



53 



labris Muls., Adalia bipunctata L., and Chilocorus bivulnerus Muls. 

 Both larvae and adults feed on the plant lice. 



The larvae of the syrphid flies (Syrphidae), more generally known 

 under the name of "sweat bees," are important enemies of the pea 



Fig. 15. — Allograpta obliqua, a syrphid fly the larva of which preys upon ifacrosiphum pisi. (Original.) 



aphis. The larvae are sluglike and attack the aphis by piercing it 

 and sucking the body juices. Each larva is capable of devouring 

 many aphides in rapid succession. Johnson reports (1899) that one 

 grower in Maryland, when separating peas, sieved out 

 about 25 bushels of syrphid larva?, mostly of the spe- 

 cies Allograpta obliqua Say (figs. 15, 16), which is illus- 

 trative of the abundance of these larvae at times. The 

 adult flies are everywhere abundant in summer, and 

 especially in the neighborhood of heavy aphis infesta- 

 tions. They hover in the air and at brief intervals fly 

 rapidly, but only for short distances. Folsom (1909) 

 enumerates eight species as attacking Macrosiphum 

 pisi, namely, Ocyptamus (BaccJia) fuscipennis Say, 

 Platychirus quadratus Say, Syrphus americanus Wied., 

 S. ribesii L., Allograpta obliqua Say, Mesogramma mar- 

 ginatum Say, M. politum Say, and Sphaerophoria cylin- 

 drica Say. 



Three species of lace- wing fly larvae (Chrysopida?) , 

 namely, Chrysopa oculata Say, C. rufilabris Burm., and 

 C. plorabunda Fitch, feed on this plant louse. They 

 are predacious in the larval stage, as is the case with 

 the syrphids. The larvae are provided with a pair of 

 hollow bow-shaped mandibles or jaws, with which they 

 grasp the aphis and through which its juices are sucked. The 

 adults are pale green insects with relatively large lacelike wings, and 

 from this character the common name is derived. 



Fig. in.— Allo- 

 grapta obliqua: 

 Larva. Much 

 en 1 a r g e d . 

 (From Metcalf.) 



