INJURING THE STALK AND LEAVES. 



217 



These plant-lice have many natural enemies with 

 which to contend. Chief among these are certain 

 minute four-winged parasitic flies, the lady-beetles, 

 and harvest-spiders or daddy-long-legs. The first 

 named of these enemies are true parasites, developing 

 within the bodies of the aphides, but the rest are pre- 

 daceous insects. There are several species of lady- 

 beetles that, both in their larval and adult states, 

 prey upon the ( lorn Aphis. An idea of their general 

 appearance may be gained from Fig. 115, which 



Fig. 115. Twenty-spotted Lady-beetle: a, larva; 6, pupa; c, beetle. 



represents the three later stages of one of the smaller 

 species — the Twenty-spotted Lady-beetle (Psyllobora 

 W-maculata). It is probable, also, that great num- 

 bers of the aphides are destroyed by the harvest- 

 spiders which abound upon corn plants during sum- 

 mer. One of the commonest of these — the Striped 

 Harvest-spider — is shown, natural size, at Plate VI. 

 Remedies. — It seldom becomes necessary to re- 

 sort to artificial remedies for this insect. While it 

 could readily be destroyed with kerosene emulsion, the 

 application generally would not pay in field culture. 



