NATURAL ENEMIES. 



33 



of experiments with this mite, which is so effective in destroying the 

 jointworm in the East, were unsuccessful, as it was found that the 

 mites would not attack either the larvae or the pupae. They fed 

 freely upon the eggs of the weevil, where these were easily accessible, 

 but they seemed unable to gain access into many of the egg masses 

 through the ordinary egg punctures. A single egg did not furnish 

 sufficient food to bring 

 one mite to maturity, 

 and it would therefore 

 necessarily perish; but 

 where there were clus- 

 ters of eggs in contact 

 with each other, the 

 female mite was able to 

 shift her body about 

 sufficiently to devour 

 more than one egg and 

 was thus enabled to 

 reproduce. In the field, 

 when placed in cages 

 with an abundance of 

 eggs of the alfalfa wee- 

 vil, the mites appeared 

 to make considerable 

 headway in overcoming 

 the weevil, but in no case 

 could the effects of their 

 attack be traced farther 

 than 2 feet from the cage 

 where they had been 

 confined in the fields. 



A little mite (Trombidium) was found attached to the adult weevil 

 beneath the wing covers, and while it was observed quite commonly 

 in late summer and fall, so far as observations indicated it did not 

 appear able to kill the host insect. A predaceous mite, Erythr&us 

 arvensis Banks (fig. 14), was foundby Mr. Ainslie feeding on eggs of 

 the weevil in the egg punctures. The economic value of this species 

 is as yet very obscure. Spiders are occasionally found feeding upon 

 the larvae in the fields. Lace-wing flies (Chrysopa) fed upon the 

 larvae in confinement when forced to do so, but preferred aphides. 

 They were not observed to attack the weevil in any form in the fields. 

 26200°— Bull. 112—12 3 



Fig. 14. 



-A predaceous mite, Erythrxus arvensis: Adult, 

 enlarged . ( Original. ) 



Greatly 



