U 1 B F 



BECEIV 



MARtH^93g ( X)6pWtl 

 UNITED STATES DEPARTMENT OF AGRICULTURE 

 WASHINGTON, D.C. 



INSECT PARASITES AND PREDATORS OF INSECT 



PESTS 



By Curtis P. Clausen, senior entomologist, in charge. Division of Foreign 

 Parasite Introduction, Bureau of Entomology and Plant Quarantine 



CONTENTS 



Page 



Introduction 1 



Control of insect pests by parasites and pred- 

 ators 2 



Enemies of aphids, scale insects, and mealy- 

 bugs 3 



Ladybird beetles 3 



Lacewing flies 8 



Hover flies 9 



Internal parasites 10 



Page 



Parasites of caterpillars 12 



Parasites of white grubs 13 



Egg parasites 15 



General insect feeders 17 



Hyperparasites 21 



INTRODUCTION 



The insects usually noticed by those engaged in the growing of 

 plants, whether farmers or gardeners, are the forms that feed upon 

 the plants or plant products and are consequently injurious. There 

 are, however, a very large number of insects that are entirely beneficial 

 in their relation to crop production. This circular deals only with 

 those species which, by preying upon or parasitizing other insects, 

 aid in preventing damage to agriculture. In general, it may be 

 stated that practically every insect in its native home has one or 

 more species which prey upon it and are dependent upon it for their 

 existence. Were it not for these parasites, many of our insect pests 

 would be able to increase to such an extent that the growing of crops 

 would be impossible. Insects have such an enormous capacity for 

 increase that some very definite checks are necessary to keep them 

 within bounds. When it is realized that some insects, such as the 

 aphids, are able to complete a generation in a week or less, it is clear 

 that they would very quickly become excessivety abundant if no 

 restraining influences were present. While climatic conditions are 

 usually the most important factor in reducing the numbers of an 

 insect pest, yet under suitable conditions the parasites and predators 

 are of nearly as great importance. In most cases these factors pre- 

 vent the plant-feeding insects from becoming excessively injurious, 

 and only a very small proportion of these species of insects ever be- 

 come sufficiently abundant to cause injury to crops. 



This circular is intended to present a general account of the vari- 

 ous forms of insects that prey upon or parasitize other insects. The 



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