88 
WHITE FLIES INJURIOUS TO CITRUS IN" FLORIDA. 
Table XVIII.— Com? 
abundance of Aleyrodes citri and Aleyrodes nubifera in 
roves infested by both species. 
Grove Nos. 
Tangerine. 
Grapefruit. 
Orange. 
Grapefruit and 
orange. 
Citri per 
leaf. 
Nubifera 
per leaf. 
Citri per 
leaf. 
Nubifera 
per leaf. 
Citri per 
leaf. 
Nubifera 
per leaf. 
Citri per 
leaf. 
Nubifera 
per leaf. 
1 
44.2 
7.5 
1.6 
1.4 
2 
33.2 
4 
14.5 
4.6 
0.5 
1.2 
.4 
.2 
3 
4 
5 
6 
8.8 
2.4 
11.2 
21. 
1.1 
1.6 
8 
9 
33 
30 
.56 
7. 
10 
11 
.9 
.2 
.8 
3.7 
Average. 
Per cent 
22.5 
86.7 
3.6 
13.3 
3.7 
59.6 
2.5 
40.3 
19.9 
97.7 
.59 
2.3 
16.1 
92.6 
1.3 
7.4 
Owing to the great attraction of new growth for the cloudy- winged 
white fly, which is discussed elsewhere, the scarcity of new citrus 
growth at certain seasons which causes concentration on water 
shoots, and other factors, this species, when it occurs by itself in a 
tangerine or orange grove, does not as frequently as the citrus white 
fly cause noticeable blackening of the foliage before the middle of 
June. At the end of the season the cloudy- winged white fly by itself 
may cause tangerine and orange trees to become as heavily blackened 
with sooty mold as the citrus white fly when the latter is at its great- 
est abundance. As has been stated, the cloudy- winged white fly is 
more likely to heavily infest grapefruit trees than is the citrus white 
fly. The cloudy- winged white fly seems to be subject to more exten- 
sive fluctuations from year to year, aside from the effects of fungus 
parasites, than is the citrus white fly, and frequently after infesting 
an orange grove for several years fails to cause enough injury to 
make washing of the fruit necessary or to make necessary the wash- 
ing of more than one-fourth or one-third of the crop each year. 
As a whole, the injury is not as extensive in groves where the 
cloudy-winged white fly occurs alone as in groves where the citrus 
white fly occurs alone. When the two species become well estab- 
lished, the former does comparatively little damage except to grape- 
fruit. The authors would estimate that there are about 5 per cent 
of the orange and tangerine groves in the State infested by the 
cloudy-winged white fly that are not also infested by the citrus 
white fly, and that there are in addition 1 per cent of orange and 
tangerine groves infested by both species but in which the citrus 
white fly has not as yet attained injurious abundance. The average 
damage from the cloudy- winged white fly is estimated at about 10 
to 15 per cent lower for oranges where that species alone infests the 
grove than where the citrus white fly is the species concerned. For 
