INSECT CONTROL 313 



the beak, and, as the insect grows, three moults take place ; 

 but with the first moult the legs are lost, so that further 

 locomotion is rendered impossible. At the third moult 

 the pupal stage is attained, and this is the most obvious 

 period of the insect's life-cycle. The first formed pupa is 

 pale green and transparent, but as the changes within the 

 pupal skin take place it becomes more and more opaque, 

 and before maturity is attained a bright orange spot 

 appears on the back of the pupa, and a little later two 

 purple spots towards the anterior end. These purple spots 

 are the eyes of the adult. The fully developed pupa case, 

 now about the size of a pin's head, splits down the back 

 and the light orange-yellow coloured, four- winged adult 

 emerges. 



It has been mentioned that the citrus white fly damages 

 the trees by sapping their vitality, but it also causes 

 indirect injury in the following manner. Like many 

 insects that derive their nourishment by, as it were, 

 embedding their mouths in the plant on which they live 

 and sucking its juices, these insects secrete a sugary 

 liquid, known as honeydew, which forms the nutritive 

 medium of a sooty mould. The fungus growth does more 

 damage to the plants than the insects themselves, per- 

 vading, as it does, not only the leaves but the branches 

 and even the fruit itself. 



Seeing that more than forty- five per cent, of the citrus 

 groves in Florida are infested with white fly, estimated 

 to cause a loss of from forty-five to fifty per cent, of the 

 value of an orange crop, it is hardly surprising that 

 scientists called to mind the success of the little Australian 

 beetle against the cottony cushion scale and turned their 

 attention to hunting for another benefactor to come to 

 the rescue of their orange crops. 



In 1910 the American Congress made a special grant 

 towards a world-wide search for the native home of the 

 citrus white fly and the collection of its natural enemies, 



