118 INSECTS INJURIOUS TO STAPLE CROPS. 



destroy so many as to prevent serious injury. The effect 

 of these parasites and predaceous insects is indeed marvel- 

 lous and is always a matter of observation to the farmer, 

 who wonders if they are to finish the work of the lice and 

 utterly destroy the crop. Prof. Webster says of them: 

 "The effect of the parasites upon the grain-louse was 

 simply astonishing, while their numbers were myriad. 

 Going to the fields of recently harvested grain, if one stood 

 in a position to bring the newly made shocks between 

 himself and the setting sun, he could clearly observe the 

 swarms of minute hymenoptera arising therefrom and 

 flying away. Besides, the stubble-fields were overrun with 

 lady-beetles and their larvae. ^' Several internal parasites 

 belonging to the family Braconidm (see page 41) are con- 

 cerned in this good work, one variety, described by 

 Prof. A. J. Cook as Aphidiiis granariaphis (Pig. ^Q), 

 having been especially namerous in 'Michigan in 1889. 

 All the common ladybird-beetles feed upon these lice, and 

 with an abundance of food increase in numbers very 

 rapidly. Several species of syrphus-flies and Clirysopa are 

 equally fond of them, and are very numerous in infested 

 fields. 



Remedies. — As far as known no artificial remedy for the 

 Wheat-louse has yet been found. Though the lice might 

 be destroyed with various sprays, this is hardly practicable 

 in a wheat-field; and inasmuch as the lice breed upon so 

 many species of the grass family, there seems to be no cul- 

 tural method for combating them. Ordinarily, therefore, 

 we will have to trust to the good woebnrk of the eficial 

 insects and diseases to prevent their depredations. 



