184 GYPSY AN'D BROWN-TAIL MOTHS. [Jan. 



SPECIAL REPORT ON IMPORTING PARASITES. 



BY A. II. KlKKLAND, Sill>< fillti lult ut. 



The study of insect parasitism opens up one of the most in- 

 teresting fields in the whole domain of nature, -- a study full 

 of interest and surprises, and often of great practical value in 

 its results. Nearly every insect has enemies of its own kind, 

 remote relatives, they may be called, which prey upon it and 

 attempt to destroy it. The result of their work is shown by the 

 abundance or scarcity of their unwilling hosts. We note that 

 some years are " caterpillar years," for example, and that others 

 are not. The abundance or scarcity of any caterpillar depends 

 in large measure upon the presence or absence of the parasites 

 which attack that particular insect. Other factors, such as the 

 work of insectivorous birds, bacterial and fungous diseases, also 

 play an important part, but the influence of insect parasitism 

 in the long run controls the situation. 



The army worm, a pest of grass and grain fields, gives a good 

 illustration. This insect at long intervals appears in tremen- 

 dous numbers, only to disappear for many more years. It is 

 notably attacked by a certain fly, which lays its eggs on the 

 ".worms," these eggs in turn hatching into grubs, which enter 

 the bodies of their hosts and kill them. \Vhcn the worms are 

 abundant, there is offered a wealth of food for the parasite-. 

 They multiply prodigiously, destroy their hosts, and in a season 

 the army worm outbreak becomes a thing of the past. The fol- 

 lowing year there is a multitude of parasites, and but little 

 food for them. 



A- a result, the parasite flies die off; the few remaining 

 army worms increase slowly in swamp< and along the banks of 

 Streams, until after the lapse of years their numbers arc suffi- 

 cient to lay the foundation for another army worm outbreak, 

 and this in turn i- followed l.y the development of a multitude 



