8 IMPORTED PARASITES. 



egg (or deposited by the female parasite, for in quite a large 

 number of them the eggs hatch within the body of the parent), 

 ultimately becomes established within or upon the body of the 

 other insect, which serves as host ; and, although there is consid- 

 erable variation in the ways by which this is accomplished, the 

 end is the same. 



Having become established, the young larva proceeds to feed 

 upon the less vital portions of its victim, usually upon the fatty 

 tissues, until it is nearly or quite full grown; then, from its 

 point of vantage inside the body of its host, it kUls it, devours 

 all or such portions of its body as it desires, and later trans- 

 forms to a pupa, which in turn produces an adult similar to 

 that which made the original attack. 



There is hardly a plant or shrub or tree which is not attacked 

 in some portion by one or more species of plant-feeding insects. 

 Some trees, like the oak and pine, support a very great variety, 

 which are widely diverse in their habits, and each of which con- 

 fines its attack to a limited portion of the tree. Those which 

 bore in the bark, for example, are always different from those 

 which feed upon the foliage or which are nourished by the seed. 

 Similarly, there is hardly a single plant-feeding insect which is 

 not attacked by one or more different parasites, each of which is 

 limited in its attack to some stage in the development of the par- 

 ticular species which serves as host. The parasites which attack 

 the caterpillars of a plant-destroying insect, like the gypsy moth, 

 never attack the pupae or the eggs ; but there are other parasites 

 which do attack these stages. 



Plant-feeding insects very rarely attack more than a few sorts 

 of plants or trees. Some, like the gypsy moth, are very general 

 feeders, and will eat the foliage of pine and fir as well as of oak 

 and birch ; but the number which feed upon both pine and oak 

 are very few, and even the gypsy moth displays a strong prefer- 

 ence for the foliage of broad-leaved trees. There are a great 

 many which will feed upon nothing but oak, and there are many 

 which are even more restricted, and which are never found on 

 more than one kind of oak. Exactly the same is true of the 

 parasites : some are general feeders, and will attack a great va- 

 riety of hosts ; others are extremely particular in this respect, 

 and will not attack, or, if they are forced to attack, their young 



