2 BULLETIN 645, U. S. DEPARTMENT OF AGRICULTURE. 
parasitic on certain injurious insects, excellent as they are, have 
fallen short of what was expected of them, but more as a result of a 
spraying system developed by the writer, which, by taking all pests 
into consideration instead of merely the white flies, has proved the 
direct financial gain that will follow the intelligent application of 
spray mixtures. It is to certain advantages of this system of spray- 
ing that attention is called in this bulletin. Perhaps the best argu- 
ment in favor of spraying is to be found in the difficulty experienced 
in securing the same grove for demonstration purposes two or three 
years in succession. Once the owner has seen with his own eyes the 
benefits resulting from careful and well-timed spraying, he refuses 
to accept the losses that he knows will come to him or his company 
through the setting aside of blocks of trees to serve as checks in com- 
munity demonstration work. 
PESTS OF IMPORTANCE. 
Of the total damage caused by insects and mites to citrus in 
Florida, more than 95 per cent may be attributed to six species. In 
the order of their destructiveness, these are the citrus white fly,’ the 
purple scale,? the rust mite,? the red scale, the cloudy-winged white 
fly,> and the red spider. There are several other pests of secondary 
importance, such as the woolly white fiy,’ the purple mite,® and the 
chaff scale. The citrus white fly now infests nearly all the groves 
in the State. The purple scale is found in greater or less numbers on 
every citrus tree. 
INJURY TO TREES AND FRUIT. 
The presence of these pests on the trees and fruit produces 
blemishes which cause fruit to be placed in a much lower grade than 
would be the case if these blemishes were not present. While the 
excellent methods of washing the fruit remove nearly all the sooty 
mold which follows attacks of the white fly, usually some of it is left 
near the stem end. When this is present the fruit is placed in a grade 
lower than if it were absent. The presence of scale insects on the fruit 
lowers the grade, and, when these are abundant, makes the fruit 
practically unmarketable unless the scales are removed by hand wash- 
ing. Perhaps the greatest cause for lowering the grade of fruit is 
the blemish following rust-mite injury. All these pests devitalize the 
trees, and this type of injury is much more important than the low- 
ering of the grade of the fruit, because the yield is reduced. This 
1 Dialeurodes citri Ashmead. 6 Tetranychus sexmaculatus Riley. 
2 Lepidosaphes beckii Newman. 7 Aleurothriaus howardi Quaintance. 
® Hriophyes oleivorus Ashmead. 8 Tetranychus citri McGregor. 
4Ohrysomphalus aonidum Lipneus. 9 Parlatoria pergandii Comstock 
> Aleyrodes nubifera Berger, now known 
as Diateurodes citrifolii Morgan. 
