40 



As in the case of the orange, the rind of the lemon is hardened and 

 toughened, but the juicy contents are not affected materially; further- 

 more, a silvered lemon will keep very much longer than a perfect 

 lemon, and will bear long shipment without risk of much loss. Until 

 very recently the rusted lemon in southern California found no market 

 whatever, and was a total loss to the grower. The scantiness of the 

 crop in 1900 resulted, however, in some shipments of rusty fruit being 

 made under the name of "russet lemons," about half the normal price 

 being obtained. Should the manufacture of citric acid assume very 

 much importance in southern California, the mite-injured lemons could 

 be used for this purpose. Nevertheless, considering the ease with 

 which the mite may be controlled, there is no excuse for allowing it to 

 maintain itself in injurious numbers in a lemon grove, since, irrespec- 

 tive of the appearance and value of the fruit, its work on the foliage 

 materially lessens the healthfulness and vigor of the plant. 



The rust mite avoids exposure to sunlight, and hence the lower half 

 of the fruit is nearly alwaj^s first invaded, and only gradually does the 

 mite work its way around to the upper surface, very frequently a small 

 portion exposed to the direct rays of the sun remaining unattacked. 

 This gives the appearance, most prominently shown in the case of the 

 orange, of a discolored band extending about the fruit. The multipli- 

 cation of this mite goes on at all seasons of the j^ear in the orange and 

 lemon districts, being merely less prolific and active in winter than in 

 summer. It has been supposed in Florida that dry weather is inimical 

 to it, but the fact that it thrives in southern California would seem to 

 throw doubt on this belief. 



The rust mite itself is very minute (fig. 33), practically invisible to the 

 naked eye. It is honey -yellow in color, and about three times as long 

 as broad. It is provided with four minute legs at its head extremity, 

 by means of which it drags its wormlike body slowly from one spot to 

 another. The eggs are circular and are deposited singly or in little 

 clusters on the surface of the leaf or fruit. They are about half the 

 diameter of the mother and nearly transparent in color, having, how- 

 ever, a slight yellowish tinge. They hatch in four or five days in hot 

 weather, but in cold weather the egg stage may last for one or two 

 weeks. The newly hatched mite is very similar to the adult. About 

 a week after hatching, it undergoes a transformation, or molt, requir- 

 ing a period of about forty-eight hours, after which it escapes from 

 the old skin, which remains adhering to the leaf or fruit for some little 

 time. This moult brings the mite to its adult stage, in which it is 

 somewhat darker in color than the 3'^oung and opaque. No sexual 

 differences have been discovered, and the number of eggs deposited 

 by a single mite is not known. The entire development of the mite 

 is short, probably not much exceeding, in warm weather, two weeks. 



The food of the mite seems to be the essential oil which is abundant 



172 



