41 



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 con- 

 ditions 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 distributed 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 ineffective 

 against the eggs. The sovereign remedy for the rust mite is sulphur. 

 It may be applied as a powder on trees, and, moistened 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 at once. A better method, 

 perhaps, is to first dissolve the sulphur with lye, as follows: 



Mix 20 pounds of flowers of sulphur into a paste with cold water, 

 then add 10 pounds of pulverized caustic soda (98 per cent). The dis- 

 solving lye will boil and liquefy the sulphur. Water must be added 

 from time to time to prevent burning, until a concentrated solution of 

 20 gallons is obtained. Two gallons of this is sufficient for 50 gallons 

 of spray, giving a strength of 2 pounds of sulphur and 1 of lye to 50 

 gallons of water. An even stronger application can be made without 

 danger to the foliage. This mixture can also be used in combination 

 with other insecticides. 



There are several species of mites which attack citrus plants, the 

 most troublesome one of which, especially in Florida, is the one named 

 above. Almost any insecticide will kill the adult mite, such as kero- 

 sene emulsion, resin wash, or even a simple soap wash, but unless the 

 eggs are killed the trees will be reinvaded about as thickly as ever in 

 the course of a week or ten days. The advantage of the sulphur treat- 

 ment arises from the fact thnt the sulphur adheres to the leaves and 

 the young mites are killed as soon as they come in contact with it. 



THE SIX-SPOTTED MITE. 



This leaf mite or spider {Tetranychus sexmaculatus Riley— fig. 34), is 

 closely allied to the common red spider of greenhouses. It first made 

 its appearance as an important orange pest in Florida in 1880. Fol- 

 lowing the severe freeze of the winter of 1885-86, the weakened trees 



172 



