INSECTS INJURIOUS TO THE ORANGE. 339 



A tiny Ichneumon fly, the red-legged Trioxys, Trioxys 

 testaceipes Cresson, also infests this species of aphis, while a 

 third friendly parasite is a small Aphidius, a shining, black 



FIG. 399. 



fly. Were it not for these predaceous and parasitic insects, 

 the Aphides would soon multiply to such an extent as to ruin 

 the plantations. 



No. 249. The Rust Mite. 

 Phytoptus oleivorus Ashmead. 



The rust which often occurs on the fruit of the orange 

 was until of late regarded as due to a fungoid growth, but 

 recent investigators have shown that it is caused by a very 

 small, four-legged mite, which punctures the oil-cells, and the 

 exuding oil, when exposed to the influence of the atmosphere, 

 soon undergoes a change, assuming a dark, rusty appearance, 

 which seriously depreciates the value of the fruit for market. 

 To the unaided eye the oranges appear dusty, but if examined 

 with a magnifying-glass they will be seen covered with a 

 multitude of mites of a whitish-flesh color. 



A weak alkaline wash applied to the fruit would doubtless 

 destroy these mites. 



Another rust, known as " the black smut," often spreads 



