274 MISSOURI STATE HORTICULTURAL . OCIETY. 



are entitled to prominence among the insects that assist man in reduc- 

 ing the numbers of plant lice and such small but noxious pests. It is 

 unfortunate that in applying insecticides to infested plants we so often 

 unavoidably destroy our small friends with our foes. 



Jt is in the true parasites, however, that nature aifords us the great- 

 est aid in keeping in check the insects injurious to vegetation. These, 

 as was remarked at the beginning of this paper, are mainly Hymen 

 opterous or Dipterous. The species belonging in the first named Order 

 are four winged flies, bearing a distant resemblance in form to wasps, 

 but the females are usually provided with a conspicuous, excerted ovi- 

 positor at the tip of the abdomen, by which their eggs are inserted un- 

 der or into the skin of the unfortunate caterpillar or grub, which they 

 select as a nursery for their young. The latter are footless, maggot- 

 like worms, which, upon batching, burrow in the body of their victim, 

 by a mysterious instinct avoiding the vital organs, so that their miser- 

 able host lives until their growth is completed. They are more espe- 

 cially the foes of caterpillars, but many boring beetle larv^ie are also 

 attacked. The larger species, like those that attack the Cicropia and 

 Polyphemus moths are solitary. Others, like those often observed in 

 the Tobacco or Tomato worm are gregarious and will exist in great 

 numbers in a single individual. When read}'- to transform they make 

 their way to the surface and attach their cocoons by one end to the 

 skin, and we often see caterpillars entirely covered with these little 

 snow-white cocoons. The worms thus infested live in a torpid state 

 far longer than they would have done if healthy, but never have suffi- 

 cient strength to enter the ground to transform. 



Another group of very minute four-winged flies (Proetotrypidce) 

 are Egg parasites, and destroy their victims in their earliest stages of 

 existence. Other small species infest plant lice and scale insects, caus- 

 ing the bodies of the former to become rigid as the parasite develops. 

 When the fly is perfected it cuts its way out through a small hole like 

 that made b> a fine needle. 



The most important of the two-winged parasites are flies belong- 

 ing to the family Tachinai. They have the general appearance of the 

 common house fly, some species being larger and some smaller than 

 the latter, generally more bristly, and a few have brightly colored 

 bands crossing the abdomen. Among the species of this group that 

 have rendered the most important service to man are the Colt rado 

 beetle parasite, (^Eporista loryphorcB, Riley), the army worm para- 

 site, {E. leucanm, Kirk), and the red tailed flesh fly, {Sarcophaga car- 

 naria, Linn.), which feeds upon the eggs and young of the Rocky 

 mountain locust. 



