250 ELEMENTARY ENTOMOLOGY 



and we are just commencing to learn how to utilize them in com- 

 bating imported insects. Thus the state of Massachusetts and 

 the United States Bureau of Entomology are now carrying on ex- 

 tensive experiments in the importation of the parasites of the 

 gypsy and brown-tail moths, which are very largely effective in 

 holding those insects in control in Europe. The various parasites 

 which attack the eggs and caterpillars at different stages of growth 

 have been imported ; they are reared in this country until suf- 

 ficiently numerous, and are then liberated in sections badly affected 

 by the caterpillars, with the hope that they will ultimately become 

 numerous enough to hold their hosts in check. 



Ichneumon-flies (Ichneumonidae). Any one who has attempted to 

 rear any of our large moths, such as the cecropia or polyphemus 



moths (see page 215), will have be- 

 come acquainted with the Ophion flies, 

 which commonly parasitize them. 

 They are light brown or golden in 

 color, about three fourths of an inch 

 long, and the abdomen is compressed 

 laterally, so that the back is ridged. 

 A single egg is laid on the caterpillar, 

 which lives to pupate. The OpJiion 

 larva spins a tough brown cocoon 

 within the pupal shell and emerges 

 FIG. 395. Limneria fngitiva, a f rom i t t i ie nex t spring. They belong 



parasite of the tent caterpillar. , r ., r . , n . 



(Twice natural size) tO the lar g e famil y f ichneumon-flies, 



(After Fiske) which includes most of the larger par- 



asites, though some of this family are 



quite small. The Pimpla flies are nearly the same size, but are 

 black in color and have the abdomen more broadly joined to the 

 thorax. They are effective parasites of many of our most common 

 caterpillars, such as the tent caterpillar, tussock-moth caterpillars, 

 the cotton-worm, and others. 



Braconid-flies (Braconidae). Wherever plant-lice are abundant 

 there will be found some empty brown skins, globular in form and 

 with a small round hole in each. Other individuals will be brown, 

 swollen, and dying as a result of the parasitism of little braconid, 

 flies which are developing within them. When mature the parasite 



