GALLS INDUCED BY PLANT-LICE 91 



blocking up the breathing pores. Six to eight pounds of 

 quassia chips are usually added to the mixture in the case 

 of honey-dew producing species. 



Luckily for mankind, Aphidae are kept in check by an 

 enormous number of insects. The little spotted beetles 

 known as " ladybirds " and their larvae prey upon them, 

 also the voracious larvae of the hover and lacewing flies. 

 Various hymenopterous parasites of the family Chalcididae 

 deposit their eggs in the bodies of Aphides. Ants, how- 

 ever, value them for their products, and carefully guard 

 them. The passage of ants up and down the trunk of 

 a tree is a certain indication that Aphides are present. 



