Greenhouse Insects 375 



Control. Aphids may be controlled in the same 

 way as thrips (see p. 369). They are also kept in 

 check in nature by lady beetles (fig. 8o, c) which 

 feed on thenl, and by a fly, Aphidius testaceipes 

 (fig. 80, b and d). The adult female of this fly lays 

 its eggs in the body of the aphis. The eggs upon 

 hatching give birth to a small legless larva which 

 feeds upon the interior vital parts of the plant louse. 

 When the larva is fully developed it pupates and 

 cuts a circular hole on the top of the body, emerging 

 as a winged insect ready to attack other aphids. 



Soil-Infesting Insects 



Soils infested with insect pests are as sick as when 

 infested with eelworm or parasitic fungi. The green- 

 house man in sowing his seed has often great difB- 

 culty in obtaining a good and even stand. Fre- 

 quently the stand is reduced by fifty per cent, in 

 spite of the many resowings. The cause of this may 

 be traced to the presence in the soil of certain in- 

 sect pests. Among those dreaded most are: Cut- 

 worms (Agrotis sp.), (Lycophotia sp.), (Peridroma 

 sp.); wireworms (Melanotus sp.), and white grubs 

 ( Phyllophaga sp. ) . 



Control. Spraying the soil will be of little value 

 in the control of underground insect pests. Fortu- 

 nately, however, we have more effective means for 

 dealing with them. To destroy wireworms, sow 

 com which has been soaked for ten days in water 

 containing arsenic or strychnine sulphate before 



