INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA. 



THE WALNUT BLISTER-MITE 3 

 Eriophyes tristriatus Nalepa (Family Eriophyidae) 



(Figs. 9, 10) 



Description. — The adults resemble in a general way the other mem- 

 bers of this genus, being very minute, enlarged at one end and nearly 

 pointed at the other, light greenish white and with but two pairs of 

 legs. The blisters made 

 by this mite are very 

 characteristic. On the 

 leaves of the English 

 walnut they are in the 

 form of thickened felt- 

 like pads usually lighter 

 in color, producing 

 swellings on the upper 

 and depressions on the 

 lower surfaces. On the 

 leaves of the wild 

 black walnut, however, 

 the blisters are smaller 

 in area but decidedly 

 gall-like, as shown in 

 Fig. 10. 



Life History. — Little 

 is known of the life his- 

 tory of this mite. Prob- 

 ably hibernation takes 

 place under the scales 

 of the leaf buds, as in 

 the case of the pear-leaf 

 blister-mite, but this has 

 not been proven. The 

 mites appear with the 

 leaves and at once begin 

 to work upon the undersides of them, causing the felt-like blisters. 

 which gradually enlarge as the number of mites increases. 



Nature of Work.— The illustrations (Figs. 9 and 10) show well the 

 nature of the work. Though often a source of annoyance, the attacks 

 are not extensive enough to cause any particular injury to the trees. 



Distribution.— The walnut blister-mite is exceedingly common 

 throughout the State. 



Food Plants. — The leaves of the wild black walnut and the English 

 walnut are attacked. 



Control. — Injuries by this mite are not at all severe and have not 

 warranted control measures in the past. However, if such are deemed 

 necessary, those recommended for the pear-leaf blister-mite may be 

 used. The time of application of the sprays would be just as the leaf 



Fig. 9. — Leaves of the English walnut showing 

 light-colored felt-like blisters caused by the wal- 

 nut blister-mite. Eriophyes tristriatus Nalepa. 

 Natural size. (Original) 



'Determined by Nathan Banks who also records a variety (erineus Nalepa) of 

 the above species which causes reddish blisters on the walnut leaves instead of the 

 light-colored ones. 



