136 DISEASES OF CROPS. 



sicce lays its eggs ■within the pupse of Pontia hrassicce 

 After the hatching of the eggs the parasitic larvae feed oii 

 the contents of the pupse. 



Prevention. — (1) Brushing infested plants so as to dis- 

 place the caterpillars, is a means of preventing further 

 injury. Before brushing, a small quantity of crude naph- 

 thalene should be placed round each plant. This prevents 

 the caterpillars from returning up the stems. (2) Dredg- 

 ings of sulphur and salt over infested plants have been 

 recommended for keeping off the attacks of this pest. (3) 

 Good cultivation and a liberal dressing of the most suitable 

 manures " has been found serviceable ; and the application 

 of liquid manure ■will save a crop even when badly 

 infested." 



Cure. — (1) Probably hand-picking is the most effectual 

 remedy. " Children should be encouraged to catch the 

 butterflies (as ■well as the caterpillars) and crush them, 

 and not be blamed for killing the 'poor little pretty 

 butterflies.' ' Handsome is that handsome does,' and the 

 converse to this is, in the same sense, equally true, 

 ' Ugly is that ugly does.' " (2) Syringing the plants with 

 weak solutions of salt, soap-suds, or lime is said to destroy 

 these caterpillars. (3) Watering the crops with a solution 

 of iron sulphate (2 per cent.) destroys the larvae of Pontia 

 brassicce, and is beneficial (as a plant-food) for cabbage 

 plants. (4) In the United States kerosene emulsion has 

 been used for destroying the larvae of the cabbage butter- 

 fly (Riley's Insect Life, vol. i. p. 27). 



The Small White Butterfly {Pontia rapm, Pieris 

 rapce) and The Green-veined White Butterfly 

 {Pontia napi, Pieris napi). The eggs of both these 

 butterflies are laid singly on the underside of the leaves 

 of cabbage plants. The larvae of these butterflies are both 



