INSECT ECOLOGY 381 



AFFECTING M. PISI INDIRECTLY 



raconidcB (braconids) 



Perilitus americanus, parasitic on the beetles, Ceratomegilla fuscilabris and Coccinella 



novemnotata. 

 Bassus l&totorius, a parasite bred from larvae and pupae of Allograpta obliqua and five 



other species of Syrphida. 

 7 igitida (figitids) 



Solenaspis hyalinus, a parasite from larvae of Mesogramma polita. 



ilid<z (pteromalids) 



Pachyneuron syrphi, a parasite of Bassus latotorius. 

 :yrtidce (encyrtids) 

 Encyrtus mesograpta, a parasite from larvae of Mesogramma polita. 



lidce (chalcids) 



Isocratus vulgaris, a parasite of Bassus latotorius. 

 'roctotrypida (proctotrypids) 



Telenomus podisi, a parasite of the eggs of Podisus and Euschistus. 



A few examples will illustrate the intricacy of the interrelations of 

 these insects that are dominated by Macrosiphum pisi. 



M. pisi is preyed upon by lady beetles, the pupae of which are sucked 

 by the stink bugs, the eggs of which are parasitized by a proctotrypid. 



M . pisi is food for larvae of flower flies, the larvae and pupae of which 

 are parasitized by a braconid, which is itself parasitized by a pteromalid 

 and a chalcid. 



M . pisi is destroyed by larvae of flower flies, the larvae of which are 

 attacked by stink bugs, while the adults are eaten by robber flies, toads, 

 and various birds, as the kingbird, flicker and phoebe. 



Thus forty species of insects are known to be vitally concerned with 

 the pea louse. There should be added the mite, Rhyncholophus parvus, 

 which feeds on the louse. 



The writer has found more than two hundred species of insects in a 

 field of red clover, All these have some influence on the pea louse 

 (clover louse) and on each other; though the influence is often remote in 

 its effects and practically insignificant. The scavenger insects on the 

 ground, and collembolans etc., in the soil, feeding on organic matter, 

 affect the texture and composition of the soil and consequently the 

 plant. Without considering earthworms, moles, mice, birds and many 

 other animal factors that might be thought of, we shall mention insects 

 only. The bees that pollenize the flowers, and the various insects that 

 destroy the roots, stems, leaves or flowers, all affect indirectly the louse. 

 As illustrating interactions, though it is of no practical consequence, 

 we may say that the yield of clover seed depends slightly upon the struc- 

 ture of the milkweed flower; for flower flies whose larvae destroy plant 



