352 POPULAR SCIENCE MONTHLY 



THE UTILIZATION OF AUXILIARY ENTOMOPHAGOUS 



INSECTS IN THE STRUGGLE AGAINST INSECTS 



INJURIOUS TO AGRICULTURE 1 



By Professor PAUL MARSHAL 



THE NATIONAL AGRONOMICAL INSTITUTE, PARIS 



I. The Role of Entomophagous Insects in Nature 



IF phytophagous insects could develop and multiply without hin- 

 drance in proportion to their natural reproductive power, in a 

 short time they would cause all species of terrestrial vegetation to 

 disappear. The multiplication of these destructive forms is very 

 fortunately kept within limits compatible with the existence of plants 

 by the presence of other insects, predatory or parasitic, which places a 

 check on their propagation. 



The capacity for prolification of entomophagous insects is itself 

 very considerable : their eggs may often be counted by hundreds or 

 even by thousands; moreover, as several of the species of parasites 

 often attack a single species of plant-feeding insect, it is certain that 

 the latter would in its turn become very rapidly annihilated if the 

 parasites were not themselves held in check by hyperparasites, and if 

 they were not repressed in their spread by all the obstacles that render 

 their struggle for existence more difficult than can be imagined. 



The role of entomophagous insects is of the first importance, whether 

 from the point of view of the economy of nature or from the point of 

 view of utility to man. 



Some, like the Carabida? and Coccinellidse, are predatory. They 

 destroy for food the insects which they attack, and the benefit derived 

 from their action is immediate. 



The others, which are represented both by the hymenopterous 

 and dipterous parasites, lay their eggs in the interior of developing 

 insects, or in their near neighborhood, and the larvae which hatch from 

 these eggs nourish themselves at the expense of their hosts, accomplish- 

 ing their death at a more or less advanced stage of their evolution. In 

 this case the benefit brought about is sometimes immediate, as in 

 certain species of minute Hymenoptera (Teleas, T etrastickiis , etc.) 

 which lay their eggs in the interior of eggs of other insects and 



1 Translated from " The Annals of the National Agronomical Institute " 

 (Superior School of Agriculture), Second Series, Vol. VI, Part II, Paris, 

 1907, pp. 281-354. 



