366 REPORT OP THE COMMISSIONER OF AGRICULTURE. 



they at all times show a marked preference for light, they desert those 

 parts of leaf or fruit upon which it falls brightest. On a leaf partially 

 exposed to the sun, the mites congregate near one edge in the morning, 

 and in the afternoon cross to the opposite side of the same surface, fol- 

 lowing the shiftiug shade which, by reason of its curvature, the edges 

 of the leaf throw upon one side or the other. 



Rings of Rust on Fruit. — On the fruit, this preference of the mites for 

 half shade, causes a phenomenon which will be recognized as very com- 

 mon on rusty oranges. This is the occurrence of rust in a well-defined 

 ring obliquely encircling the orange, as the ecliptic does the earth. The 

 rnst ring is seen most plainly on fruit from the upper portion and south 

 side of a tree when it stands with others in a grove, and will be found 

 to mark the band of half shade, between the portion of the orange most 

 directly exposed to the sun's rays and that in densest shadow. The 

 surface covered by this penumbra band is precisely that upon which 

 the mites gather most thickly in the middle of the day. Here their 

 attack upon the rind will be most severe and its after effects most 

 noticeable. (Plate I.) 



There is also observable in rusted fruit a marked difference in the 

 amount of discoloration upon the opposite sides. Even where no 

 plainly-marked ring is visible, the side of the fruit which, upon the 

 tree, was turned towards the sun, frequently presents a bright spot, 

 and the opposite side an area of lighter bronze, with less sharply de- 

 fined boundaries. 



These facts, taken in connection with the observed habits of the mites, 

 may be regarded as the strongest evidence showing a connection be- 

 tween rust and their attacks upon the fruit. 



Influence of Weather. — It has been already observed that the hatch- 

 ing of the eggs, although retarded, does not cease in cold weather, and 

 that the breeding continues throughout the year. Frost, which is some- 

 times severe enough to kill the adult mites, does no injury to the eggs, 

 and tne severity of a winter has little if any effect upon the prevalence 

 of the mites during the following summer. In droughts, however, there 

 is some evidence that many of the eggs dry up and are exterminated. 

 The extremely dry seasons of 1881 and 1882 have been followed in the 

 winter of 1882-'83 by the brightest crop of fruit that has been known 

 for several years. 



Agencies which assist in the Distribution of the Mites. — The activity of 

 the mites and their readiness to climb upon anything they meet in their 

 path, renders it evident that any living creature which passes from one 

 tree to another is competent to transport the mites with it. The tail 

 feathers of birds must sweep thousands from the surfaces of the leaves, 

 and spread them from tree to tree or from grove to grove. 



So readily do they relinquish their hold when brought into contact 

 with a moving body, that the point of a needle swept across the surface 

 of an infested leaf will usually be found to have several mites adher- 

 ing to it. 



The same agencies which assist in the spread of scale-insects un- 

 doubtedly serve to scatter the mites. Not only do they climb readily 

 along the web of spiders, but they may frequently be seen upon the 

 bodies of the spiders themselves, which do not seem to be at all disturbed 

 by the restless movements of their little attendants. 



The wandering habit of spiders is well known. ■ Their method of 

 bridging great distances by casting out hundreds of feet of silken line, 

 to be wafted by the winds and caught in distant trees, has often been 

 noted. There is little doubt that of all other modes of dissemination, 



