430 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



within the egg of the host. Others such as the braconoids or ichneu- 

 mons may parasitize the larvae. The larval parasites are frequently 

 quite specific, and a high percentage of the host species may be de- 

 stroyed. As an example of this type of parasitic control, the soil 

 under a tree or plant may be so completely covered by the empty 

 cocoons of braconid parasites that the surface appears white. An 

 experience encountered a few summers ago is further evidence of the 

 percentage of parasitism. An attempt was being made to secure a 

 number of normal sphinx moth larvae on catalpa. Several hundred 

 individuals were collected from a small area of concentrated plantings, 

 and during the examination of some 300 specimens not a single larva 

 was found free from parasites. 



These parasites are of enormous value to man in the continuous 

 combating of almost every important economic insect pest. Many 

 other insects would probably become important pests if it were not for 

 the parasites that constantly hold them in check. One of the most 

 interesting and remarkable examples of the importance of insects as 

 natural enemies is the almost exclusive use of insect parasites and 

 predators in the control program of orchard insects in the fruit area 

 at Kentville, Nova Scotia, Canada. 



Insects as scavengers. — The insect scavengers are those which feed 

 upon decomposing plants or animals, or on dung. Such insects assist 

 in converting these complex organic materials to simpler chemicals 

 which are returned to the soil where they are available to plants for 

 the production of new organisms. 



Carrion-feeding insects such as blow flies, carrion beetles, rove 

 beetles, skin beetles, and others are of value in removing or often 

 burying carrion. Dung beetles of several families and dung flies 

 hasten the decomposition of dung. Insects such as termites, carpenter 

 ants, wood-boring beetles, and other wood feeders are important agents 

 in hastening the conversion of fallen trees, logs, and stumps to soil. 

 The galleries of these insects serve as avenues of entrance for fungi 

 and other organisms of decomposition which hasten the breakdown of 

 the wood. 



"We have observed the organic cycle in nature since our earliest recol- 

 lections and as a result have accepted this condition without further 

 thought. The value of insect scavengers can be best emphasized by 

 asking how long we would be able to survive in a world where dead 

 bodies of plants and animals were not broken down and returned to 

 soil and where the earth's surface would as a result in time become 

 covered to a depth of several feet with such organic waste. These 

 insect scavengers are indeed essential to maintaining a balance in 

 nature. 



Importance of soil injects. — Many types of insects spend part or 

 all of their lives in the soil, where many life activities and processes 



