THE MONTHLY BULLETIN, 



263 



the vital tissues of the former being reserved until the larvae are nearly 

 ready to pupate. 



The entire larval period is passed within or upon the host. The 

 pupal stage may be passed within the host or attached or not attached 

 to it. 



There are great variations in the time of development, there being 

 but one generation a year in some and many in others. The adults are 

 usually four-winged insects with quick power of flight and great 



^,,--.^IJm 



^ J 



^ 



Fig. 262. — Mummied bodies of tlie citrus apliid (Toxoptera aurantia' Kocli), sliow- 

 ing exit holes of the internal parasites. (Bssig, P. C. Jr. Ent. ) 



activity. Many of the smaller species have the ability to jump not 

 unlike fleas. 



The work of all true parasites is rather spasmodic because of the very 

 nature of their existence. Naturally with the decrease in the numbers 

 of the hosts, the parasites die from lack of food and may be so reduced 

 in numbers that they are not able to check the rapidly increasing 

 numbers of the hosts and a plague of grasshoppers, army worms or 

 scale insects may result. 



Unfavorable weather conditions and the work of secondary parasites 

 are also often responsible for the poor showing of these beneficial 

 friends. 



