^STATURAL ENEMIES. 
33 
of experiments with this mite, which is so effective in destro3'ing the 
jointworm in the East, were unsuccessful, as it was found that the 
mites would not attack either the larvae or the pupse. 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 tlie 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, Erythrseiis 
arvensis Banks (^g. 14), was found by 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 larvse 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, ErytJirseus arvensis: Adult, 
enlarged. (Original.) 
Greatly 
