THE CITRUS WHITE FLY: DISTRIBUTION. 95 
ordinarily the expense of the fertilizer necessary to maintain orange 
trees in good productive condition varies from 10 to 20 cents per box 
of fruit produced. The wide range given is largely due to differences 
in soil conditions. Mr. E. O. Painter, in response to an inquiry on 
the subject, writes that citrus trees infested with white fly in his 
opinion require at least 15 per cent increase in fertilizer for best 
results under the circumstances. On the basis of cost of fertilizer 
amounting to 10 to 20 cents per box and an increase of 15 per cent 
due to white fly infestation, the extra expense which may be charged 
as white fly injury amounts to 1.5 to 3 cents per box. 
Cost of control measures properly chargeable to increased cost of main- 
tenance.—Estimates based on the experience of the writers in fumi- 
gating and in spraying for the white fly give the range in expense of 
the former method of control as 5.5 to 14 cents per box of oranges 
produced, and of the latter method 12.5 to 20 cents per box. These 
estimates refer to thorough control, with the result that production is 
entirely unaffected by the white fly. The minimum estimate on the 
expense of fumigation refers to groves so located that the migrations 
of adults from outside groves does not make treatment necessary more 
than once in two years. The maximum estimate refers to conditions 
where treatment every year is required to prevent loss. Increase in 
production, due to destruction of scale-insect pests, is not taken into 
consideration. In the estimates of expense of control by spraying 
the minimum estimate refers to cases where three applications of in- 
secticide per year have resulted in satisfactory control. This result 
can be attained only after the insect has been brought into complete 
subjection, such as referred to in the introductory paragraph of the 
subject of artificial control. Insecticides costing more than 14 cents 
per gallon when mixed ready for application have not been taken 
into consideration. 
DISTRIBUTION. 
As has been shown in the historical review, the citrus white-fly 
at present is generally distributed in North America. In the north- 
ern part of the United States it occurs in greenhouses, and in the 
southern part, and in limited districts in California, it occurs on 
citrus, China trees, privet, cape jessamines, and other food plants. 
In the present publication we are concerned only with the distribu- 
tion of the species in the citrus fruit-growing regions of the United 
States. 
IN THE UNITED STATES. 
According to the statistics of the Florida commissioner of agricul- 
ture, in 1905 there were 17 counties in the State reporting more 
than 5,000 bearing citrus fruit trees. In all but two of these, Dade 
and St. Lucie, the citrus white fly (Aleyrodes citri) occurs to a greater 
