BIRDS AND INSECTS 169 



Of these natural enemies the birds, the moles, the 

 centipedes, and others play an important part; but, 

 generally speaking", it is predaceous insect larva? and 

 parasitic insects that are most destructive of insect 

 life. One family alone, the Ichneumonidag, is re- 

 sponsible for the destruction of a very large per- 

 centage of some of the most virulent of our insect 

 pests ; in fact, it may be said that if, in this war that 

 we are waging for the protection of our food crops, the 

 Ichneumons were to make a separate peace with the 

 enemy, we should be starved into submission in 

 twelve months. It is important, therefore, in con- 

 sidering any proposed method for dealing with an 

 insect pest, to find out what other insects are parasitic 

 upon it, and to take into consideration the effect of 

 the method on the insect parasites. 



For instance, in some cases "it may be highly 

 injurious and superfluous to apply insecticides, as 

 they also destroy the beneficial insects which are 

 already acting as a check on the injurious species". 1 



There is no reason to suppose that the disk method 

 of protection would materially interfere with the 

 beneficent work of the parasites of the root maggot, 

 but nevertheless it was deemed necessary to obtain 

 as much information as possible about the number 

 and character of the insect enemies of this destructive 

 pest. It was found that the most destructive insect 

 that preys upon the root maggot is the predaceous 

 Staphylinid beetle, Aleochara bilineata. It is not 

 only the adult beetle that devours the root maggot, 

 but it has now been proved that its larva bores into 

 the pupa and destroys it. 



The effect of this insect in reducing the numbers of 

 the maggot of the Chortophila must be in some cases 

 very considerable, as in one of the counts made by 



1 A. D. Imms's Quarterly Journal Micr. Science, Vol. LXI, 1916, p. 218. 



