RUST OF 7IIE ORANGE REMEDIES. 115 



Application of Insecticides. — As the Eust-mite lives exposed upon the 

 surface of the plant, neither inhabiting- a gall nor making any protec- 

 tive covering for itself or young, it is not a difiBcult matter to reach it 

 with insecticides thoroughly applied. The adult Mites are very deli- 

 cate, and readily succumb to applications of moderate strength, but the 

 eggs possess much greater vitality, and require for their destruction 

 solutions of great penetrating power. The immature Mites, while un- 

 dergoing their transformations, are also difficult to kill, and appear to 

 be specially protected by the old skin, within which their changes take 

 place. 



These three stages, the adult, the molting young, and the egg, exist 

 simultaneously at all seasons of the year. The development of the Mite 

 has bef n shown to be very rapid. The eggs hatch in four or five days, 

 the time extending rarely, in winter, to two weeks. Molting takes 

 place in seven to ten days, and lasts two days. Eggs are probably laid 

 in a few days after the molt. 



In applying remedies, it follows from these data that if the Mites 

 alone are killed, and their eggs left alive, young Mites reappear imme- 

 diately, adults are found in ten or twelve days, and fresh eggs are de- 

 posited within two weeks. If the molting Mites are also left alive, 

 very little good can be accomplished, as a fresh crop of adult Mites and 

 eggs will be produced in two or three days. 



In combating Rust- mite the difficulty in killing the eggs compels us 

 to adopt one of two alternatives. We must either use powerful insecti- 

 cides, in solutions even stronger than are required for Scale-insects, or 

 else make several applications, at short intervals, of washes competent 

 to kill the Mites only. In this way the trees may be freed of Mites, by 

 killing the young as they hatch, and not allowing any to reach the 

 adult stage and produce a fresh crop of eggs. 



The following substances have been tried and their effects noted upon 

 the Mites and their eggs : 



Whale oil soap. — The action of this substance upon the Mites is pecul- 

 iar. A trace of it in solution causes them to relinquish at once their 

 hohl upon the leaf. All other liquids that have been tried, even if they 

 kill the Mites, increase the tenacity with which they cling to its sur- 

 face. All the free * mites are at once removed from leaves dipped in a 

 solution of 1 pound to 100 gallons of water. Stronger solutions are, 

 however, required to kill them or their eggs and the dormant (molting) 

 young. 



The following experiments made in the laboratory upon infested 

 leaves, show the action of solutions of various strength. In order to 

 retain the Mites upon the leaves, the liquids were beaten into foam, 

 which was spread evenly upon both surfaces, care being taken to wet 

 every ])art of the leaf. 



(1.) Solution: 1 pound to 100 gallons. Free Mites washed from the 



* This term incladns adults aud yoaoj; not dormant, or and&rgoing transfoi-matiou. 



