Trombidiformes 157 



The mite species which are of more or less economic importance in 

 North America number about 50. Of these the pear leaf blister mite is 

 perhaps the most generally known, and one of the most important, since 

 it can put its host out of fruit production. 



The Eriophyid mites on grape lack greater importance than they have 

 largely because grapes are so consistently sulfured for mildew. Neverthe- 

 less there are two kinds of these mites known in North America, namely, 

 the grape erineum mite, Eriophyes vitis (Pgst.), and the grape rust mite, 

 Calepitrimenis vitis (Can.). The former species forms erineum patches 

 on the under surface of the leaves and there seems to be a certain amount 

 of varietal resistance to the activities of this mite shown by different kinds 

 of grapes. For example, one kind of grape which is fairly well over-run 

 with erineum patches has been observed to be interlocked with another 

 variety of grape which had few or no erineum patches. 



The grape rust mite, which develops deutogynes in the fall, has received 

 little attention in North America. 



On citrus, the rust mite, Phyllocoptruta oleivorus (Ashm.) is a pest of 

 long standing in the warmest citrus-growing areas of the United States. 

 This mite, which is on an evergreen host, winters on the leaves and pro- 

 duces no specialized hibernating forms. 



In California, the most important citrus Eriophyid pest is the citrus bud 

 mite, Aceria sheldoni (Ewing), which is to be found in practically all of 

 the citrus-growing areas adjacent to the coast in Southern California. Se- 

 verely damaged lemon trees show stunting and clustering of the young 

 growth, and severe leaf and fruit malformation. These mites leave a char- 

 acteristic brown condition in the buds in which they work. They may be 

 found developing in large numbers under fruit buttons where they also 

 leave a brown injury. 



The citrus bud mite also works on oranges and grapefruit and seems to 

 have a general range through the Pacific citrus-growing areas. Very similar 

 or identical populations damage citrus in such places as Hawaii, Australia 

 and Java. 



Peach is infested by one Eriophyid, namely, the silver mite, Vasates 

 cornutus (Banks). This mite winters around the lateral buds from 3 to 12 

 inches below the terminals, in the form of deutogynes. In the early spring, 

 these mites invade the tender growing tips, and at that time, if the host 

 plant lacks leaf glands, or if the leaf glands are not operating properly 

 (these produce a sticky secretion), the mites cause an unhealthy longitudi- 

 nal rolling of the leaves and, in some cases, numerous fine yellow dots on 

 the leaves. This injury is not to be confused with the silvering of the peach 

 leaf, which silvering occurs after prolonged feeding during spring and 

 summer. The mite feeds on both leaf surfaces and produces deutogynes 

 only in response to the temperature drop in the fall. 



