40 ECONOMIC ENTOMOLOGY 



"insects constitute the most important portion of the food of adult 

 fresh water fishes, furnishing 40 per cent, of their food," according 

 to Dr. Forbes, of IlUnois. They also furnish food for most of our birds, 

 and this food may consist of many noxious forms. 



There are also many insects that are decidedly beneficial, inas- 

 much as they prey upon injurious forms or are parasitic upon them. 

 At the present time a great experiment is being conducted in Massa- 

 chusetts for the suppression of the gypsy and brown-tail moths by the 

 importation of certain parasitic insects from Europe and Japan 

 (see Part IV). From an economic point of view it is important for 

 us to know the beneficial forms so that we may not unwittingly destroy 

 them. Few persons, perhaps, fully recognize the valuable work done 

 by the modest lady-bird beetles in keeping plant-Hce within bounds. 

 Without their intervention it is quite probable that most plants would 

 die from the attacks of the fast reproducing plant-lice. Ground-beetles 

 are also important agents in the destruction of injurious larvae, and 

 their value can hardly be estimated. 



Beneficial insects may, therefore, be classified into: 



(a) Those that prey, or are parasitic, upon injurious forms {en- 

 tomophagous) such as lady-bird beetles, ground beetles, parasitic 

 diptera and hymenoptera, etc. 



(b) Those that pollinate plants, such as bees, wasps, moths, etc. 

 {c) Those that play the part of scavengers, feeding upon dead or 



decaying organic matter, such as carrion beetles, etc. 



{d) Those that serve as food for fresh-water fishes, birds, etc. 



{e) Those that secrete or elaborate substances of commercial 

 value to man, such as honey-bee, lac insect, cochineal insect, silk- 

 worm, etc. 



Berlese divides entomophagous insects into predatory and endopha- 

 goiis. Predatory insects are those which devour other insects and their 

 eggs outside the maternal body; while endophagous insects are those 

 which enter the body or eggs of their victim and destroy them. 



Some entomophagous insects feed exclusively on one species, while 

 others feed on several species (polyphagous) . From the standpoint of 

 efficiency in the destruction of injurious species Berlese arranges them 

 in the following order : 



I. Those preying on a single species and having few enemies and 

 aflverse factors, e.g., Novius cardinalis, Prospaltella berlesei, etc. 



