122 INSECTS AFFECTING VEGETATION 



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

 half of the fruit is nearly always first invaded, and only gradually 

 does the mite work its way around to the upper surface, very fre- 

 quently a small portion exposed to the direct rays of the sun remain- 

 ing unattacked. This gives the appearance, most prominently shown 

 in the case of the orange, of a discolored band extending about the 

 fruit. The multiplication of this mite goes on at all seasons of the 

 year 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 south- 

 ern California would seem to throw doubt on this belief. 



The rust mite itself is very minute, 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 moult, 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 young 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 in all the succulent parts of citrus plants, and which is 

 obtained by the mites by piercing the oil cells with their beaks. 



These mites, while excessively minute, are capable of very active 

 locomotion, moving from one part of the leaf to another, as the 

 conditions of light and food necessitate. 



An estimate, made from actual count, indicates that the mites 

 and eggs on a single leaf in midwinter may reach the enormous 

 number of 75,000. This indicates for trees, in the active breeding 

 season of summer, billions of mites. The mite is very readily dis- 

 tributed by means of insects and birds. 



The rust mite is readily destroyed by various insecticides. The 

 eggs, however, are much more difficult to kill, and practically no 

 wash can be relied upon to reach and destroy all the eggs of this 

 mite. Experience in California indicates that gassing is also in- 

 effective against the eggs. The sovereign remedy for the rust mite 

 is sulphur. It may be applied as a powder on trees, and, mois- 

 tened by rain or dew, will adhere to the leaves for quite a long 

 period, not being readily washed off even by a hard rain. When 

 spraying is done for scale insects, the flowers of sulphur can be 

 mixed and applied with the spray, accomplishing both purposes 



