88 WHITE FLIES INJURIOUS TO CITRUS IN FLORIDA. 

TasLe XVIII.—Comparative abundance of Aleyrodes citri and Aleyrodes nubifera in 
groves infested by both species. 







Tangerine. Grapefruit. Orange. Oe and 
Grove Nos. |—— - F 
Citri per | Nubifera | Citri per | Nubifera | Citri per | Nubifera| Citri per Nubifera 
leaf. per leaf. | leaf. per leaf. leaf. per leaf. leaf. | per leaf. 
Le ee ae 44.2 7.5 1.6 TRA 6 Pie ety Pearl Re eee | eee 
ES Se es eats ee te eee | ee 33.2 O15 » 252 eee ceel oe sores 
B.S Maes se eae eee yee al eee aoe | pete ee pret ate eae es 4 Pain See | Taras 5 
UE eet S.-i CE [5 ase sta) Mago SA hos SSeS 14.5 tn SE a 
Qncecbe pene lon! Sone esas qe eco ee tale eae 4.6 Pe Beta) Pe eS o 
Gi59 Ao elects A Re oe 8.8 VE: ae Oa cert eee) epee ee ese 
(MIE MEER! eae Ae More ee) eee Ree eRe cl Ae! can eee 11.2 eit 
eee See ae an em EEE A Regt tee ey ee met) er a hee eS 21. | 1.6 
Re os ets Pc Soden Bees Sead be5- son Son GSSeSre ate 33 700) | 552802 eos = eee 
LOE 2. Ree Sense all se ese oo at eee an aia] Ane eee 30 vem Meee SI ee ee 
Wi aa, ph ey 9 2 8 BT) aeeeios =o] ents Cera! Saleen eee 
1 
Average. 2250 Pala and a0) 19.9 59 16.1 1s 
Per cent. -<2 2: 86.7 13.3 59.6 40.3 97.7 2.3 92.6 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 
erowth 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 
inore 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 
