RUST OF THE ORANGE. 109 



coines pellucid and empty at the extremities, and finally splits longi- 

 tudinally, releasing the renovated Mite. The rejected pellicle is left 

 tirmly adhering to the surface on which it rests, but is in time removed 

 by the action of the weather, and much sooner from the leaves than 

 from the rind of fruit. 



The adult Mite is slightly darker than the young in color, and be- 

 comes more opaque as it grows older. No sexual differences have been 

 distinguished, nor has the act of coupling been observed. 



Owing to the difficulty of confining the Mites without interfering with 

 the conditions necessary to their existence, it has not been possible to 

 determine the duration of their lives. It is, however, safe to conclude 

 that they live several weeks after reaching the adult stage. The num- 

 ber of eggs deposited is also uncertain, but it is probably not abnormal, 

 and the enormous populousness of their colonies must be attributed to 

 rapid development, and comparative immunity from enemies and para- 

 sites, rather than to excessive fecundity. 



Food. This evidently consists of the essential oil which abounds in 

 all succulent parts of the Orange and its congeners, and which the Mites 

 obtain by penetrating with their sucking beaks the cells that lie im- 

 mediately beneath the epidermis. That they do not feed upon the chlo- 

 rophyl is shown by the color of their intestinal contents, which has no 

 tinge of green, but a clear yellow, unmistakably indicating the source 

 from which it came. 



Wandering Habits.- While engaged in feeding, the mites remain qui- 

 escent for a length of time varying from a few minutes to half an hour. 

 They then move on a short distance and again become motionless. If 

 disturbed they have a habit of erecting themselves upon the leaf, cling- 

 ing to its surface only by the anal proleg. 



When dissatisfied with their surroundings, or when food becomes 

 scarce, they wander restlessly about, and undoubtedly travel to consid- 

 erable distances. Their rate of progress on a smooth surface is quite 

 rapid, and amounts to 10 or 12 feet per hour. It is therefore not sur- 

 prising to find them changing- their position frequently 5 disappearing 

 suddenly from one portion of a tree and appearing as suddenly in great 

 numbers upon another and distant part of the same tree. 



It is not to be understood that the Mites show any concert of action 

 in moving their colonies, or that they are in any other sense gregarious 

 than that they are usually found very thickly scattered over those parts 

 of an infested plant which offer favorable conditions for their support. 

 Thus the new growth of many orange trees becomes occupied or infested 

 by them as rapidly as the leaves fully mature, and the number upon a 

 single leaf may be estimated by many thousands. 



Numerical Abundance. The following examination, made in January, 

 will give an idea of the extent of the brood during the coldest part of 

 the Florida winter. 



From a large number of leaves of late autumn growth one was e- 



