434 



Generally speaking, predatory species are much less efficient as. 

 destroyers of other insects, either because they are themselves 

 attacked by other entomophagous insects or because they are 

 usually polyphagous. They do not persist until the last individual 

 of the species attacked has been destroyed, but migrate when food 

 begins to become scarce. Though species attacked by predatory 

 enemies are therefore subject to periods of great destruction, they also- 

 have intervals during which they multiply very rapidly and may be 

 very injurious. 



Other more or less successful experiments with beneficial insects- 

 include the introduction into the United States of Apanteles glomeratus 

 from England against Pieris rapae [see Review, Ser. A, iii, p. 277], of and 

 Calosoma sycophanta from Europe and Schedius kuvanae from Japan 

 against Lymantria dispar and Euproctis chrysorrhoea [see this Review,. 

 Ser. A, iii, p. 507]. Braconidae and Tachinidae were introduced into- 

 British Columbia in 1914 against Cirphis {HeliopJiila) unipuncta and 

 Phytomdra (Plusia) calif ornica. Ccdosoma sycophanta was introduced 

 into Sumatra in 1913, against Phryganidia californica and Chloridea 

 (Heliothis) obsoleta. In 1909-1910 a Chacidid, Trichogranmia {Pentar- 

 thron) carpocapsae, Ashm., was introduced into Turkestan against 

 Cydiu pomonella, but with httle effect, the extent of parasitism not 

 exceeding 2 per cent. A Tachinid, Ceromasia sphenophori, was 

 introduced into Honolulu against Metamasius hemipterus, a weevil 

 attacking sugar-cane ; according to Swezey, as many as 87 per cent, 

 of the injurious insects were destroyed. The value of the parasites 

 that have been imported into the United States against Anthonomus 

 grandis is considered to be great. Silvestri is acchmatising Hymeno- 

 pterous parasites of Dacus oleae (ohve fi}-) in Italy. 



In conclusion, it is considered unreasonable to expect that an insect 

 imported into a new locality can succeed in neutralising the effects of 

 an injurious species indigenous to that locality, unless there is reason 

 for crediting the existence in the world of a region where the said species, 

 though injurious elsewhere, is agriculturally harmless. If so, it is in 

 this region that the fundamental cause of this desirable state of aftairs^ 

 should be investigated. The importation of the enemies of an injurious, 

 insect is not, however, always without danger, as it may disturb a 

 state of equilibrium. The study of the injurious insect, or of its 

 allies, will provide data enabling a conclusion to be drawn as to the 

 existence of enemy organisms capable of diminishing its numbers.. 

 In many cases natural control will be found to be of no practical value 

 and waste of time may be avoided by employing artificial methods,, 

 while in others, certain endophagous insects, which elsewhere attack 

 some very injurious species with very considerable practical success,, 

 might be introduced to control the same pests or species alUed to them. 

 For example, the importation from America into Europe of certain 

 Diptera {Sarcophaga cimhicis. Towns., S. hunteri. Hough, and others) 

 said to be very efficacious against grasshoppers, should be of material 

 use in Italy. Other American species of value in Europe would be 

 the Chalcid, Telenomus ashmeadi, parasitising Pentatoma ligata, and 

 allied species ; Tachinids of the genus Admontia, parasitising 

 TipuLiDAE ; Hymenoptera {Polygnotm, etc.) against Mayetiola 

 destructor and other Cecidomjdds injuring wheat. The field is a vast 

 one, and so far, practically unexplored. 



