INSECTS INJURIOUS TO AGRICULTURE 361 



which they harbor, or the predaceous insects which destroy them. 

 This way of looking at the question is very exaggerated. It is only in 

 case where the parasites constitute restricted and very localized centers 

 of contamination that this idea can hold for these determined points, 

 admitting that it will still be possible to utilize such centers of propaga- 

 tion. In the great majority of cases, on the contrary, it must be said 

 that however useful parasites may be, the fear of destroying them ought 

 never to prevent the undertaking of all measures having for an end the 

 direct destruction of the injurious insect. Parasites act, in fact, only 

 at a more or less long maturity, and admitting that with an invasion of 

 caterpillars the majority or even all harbor in their interior larval para- 

 sites, they will none the less accomplish the greater part of their 

 depredations in a manner quite as complete as if they were not para- 

 sitized. Should we, then, allow them to devastate a field or orchard in 

 order that the parasites can, the following year, accomplish their 

 beneficent work? An intervention with destructive methods, far from 

 being dangerous, will permit us, on the contrary, always to obtain a 

 double result : first, it will immediately stop the damage and save in a 

 more or less complete manner the products of that year; and, second, 

 it is not likely in the great majority of cases that the caterpillars will 

 be more abundantly parasitized in that particular spot than in any other 

 portion of the country: and in destroying a certain number of non- 

 parasitized caterpillars, one will diminish for the whole region the 

 number of possible adults which would assure the generation of the 

 following year, and that without changing the existing proportion 

 between the parasites and the representatives of the injurious species. 



The assertion that insectivorous birds can cause more harm than 

 good by attacking either the useful species or larvae parasitized by them, 

 does not appear to us well founded and seems to us to be refuted by 

 analogous arguments. In spite of the thesis formerly proposed by 

 Perris, and ably defended of recent days by Berlese and Severin, the 

 protection of insectivorous birds appears to us not at all as susceptible 

 of thwarting the beneficent action of useful insects. 



Utilization of Indigenous Insects in the Fight against Indigenous 

 Injurious Species. — Aside from the intelligent protection which should 

 be given to beneficial insects and which, as we have just shown, can be 

 based only upon exact knowledge of their biology and the relations 

 which they have to other organized beings, can man assist in artificially 

 multiplying them, and making of them a forced subject to his will 

 which will serve him at will in the struggle against indigenous enemies 

 of cultivated plants — those which for centuries have devastated our 

 prairies, fields, orchards and forests? 



The fungous parasites and microbes have already been brought into 

 our arsenal, from which we draw against the enemies of agriculture. 

 Can we bring in entomophagous insects in their turn ? 



