PARASITES FOR INSECT PESTS. 17 



It will appear from what has been said that some excellent 

 results have been obtained in this introduction work. Very many 

 experiments have resulted negatively, and many of the insects 

 imported have not proved to be of great success, but every natural 

 enemy of an injurious species, once established, is more or less 

 of a help in the warfare against the pest. When a great success 

 is achieved like that of the introduction of the Australian ladybird 

 or the African Scutellista, the saving which results far more than 

 compensates for the expenses of long-continued travel and investi- 

 gation. 



Finally, it must be stated that in experimental work of this kind, 

 v,-hen conducted by the right men, there is no danger. The his- 

 toric cases of the introduction of the English sparrow into the 

 United States, of the East Indian mongoos into the West Indies, 

 and of the European rabbit into Australia, are often mentioned 

 in connection with these importations of beneficial insects and 

 as warnings. But parasitic insects are always parasitic upon other 

 insects and nearly always upon injurious species. Predatory 

 insects are always predatory upon other insects. There is not the 

 slightest danger that any of these importations will become destruc- 

 tive to agriculture except in the indirect way in which a secondary 

 parasite, by destroying a primary parasite, may thus liberate an 

 injurious insect from attack. Persons engaged in this work, 

 therefore, should be able readily to distinguish between primary 

 parasites and hyperparasites. 



Referring in conclusion to the importation of the natural enemies 

 of the g}T3sy moth and brown-tail moth, the speaker stated that 

 the prospects on the whole are favorable for eventual relief. He 

 stated, however, that this relief will not be speedy, and property 

 holders in the infested regions must not relax their efforts to keep 

 the injurious insects down. Observations during the past years 

 have shown that the complete defoliation which results from the 

 attacks of the insects will kill certain varieties of trees in two 

 seasons, and if work against the insects is remitted while waiting 

 for the parasites to develop, the consequent loss will be very great. 



