INSECTS INJURIOUS TO AGRICULTURE 419 



and that is that one can not count upon beneficial forms as a substitute 

 for the methods of destruction commonly used in applied entomology. 

 Their role does not consist of exterminating a species, but of main- 

 taining a natural equilibrium, or of reestablishing it when it has been 

 disturbed by human intervention. In such cases, their action can 

 make itself felt in a more or less prompt way. It may happen that, 

 immediately after having been imported into a country, they stop with 

 an extraordinary rapidity the plague which they have been brought 

 to combat. This was the case with Novius cardinalis, in California, and 

 in different countries. It was also the case for Crypotolamus mon~ 

 trouzieri, which made very rapid spread in Hawaii. It must be stated, 

 nevertheless, that this is rather exceptional and that, in general, a 

 number of years are required — the number varying according to the 

 species and to the circumstances under which it is brought — before it 

 can be completely naturalized in a given country, and before, thanks 

 to its spread, it brings about a sufficient retardation of the multiplica- 

 tion of the plant-feeding species for which it is imported, to reduce it 

 from the condition of a scourge to that of a supportable species. 



The services that parasites and predaceous species render are suffi- 

 ciently great so that there is no necessity for exaggerating them. 



Far from lulling ourselves with illusions, we should keep on the 

 watch and foresee the dangers with which other injurious species 

 menace us, such as Icerya purchasi, which may any day invade Provence 

 or Algeria on plants imported from Portugal and Italy. 



There is no doubt that, however great may be the efficaciousness of 

 a ladybird, like Novius cardinalis, it will be still better not to have the 

 enemy at all than to be obliged to fight it by the intervention of its 

 natural foe. We do not know that Novius cardinalis will with us 

 develop with the success which marked its spread in California, in 

 Portugal, and in Italy. We are ignorant whether the climatic influ- 

 ences or some parasite, recently adapted to this new strange host, will 

 not limit its propagation and diminish its beneficial action. Finally, 

 other plagues than Icerya menace us, and it is unfortunately certain 

 that not all of these may be mastered by the equivalent of Novius 

 cardinalis. 



Confidence in the assistance which we can get occasionally from 

 parasites and predaceous insects should not make us lose all prudence 

 nor prevent us from seeking a guard against the perils which surround 

 us, in organizing at our large ports an inspection and disinfection 

 service like those which have been started at foreign ports, notably 

 Hamburg, and in a general way taking every measure possible to protect 

 our crops. 



