CONDITIONS FAVORABLE OB NECESSARY. 11 
deposited by these adults may have time 4 to hatch. It is impractica- 
ble to attempt to destroy t ho egg stage by fumigation, or as a rule by 
any other direel means. The scale-like stages, however, technically 
known as the larval and pupal stages, are readily destroyed when the 
dosage is properly estimated, hi Florida the month of January is, 
everything considered, the most favorable month for fumigating for 
the white fly. Ordinarily it would probably be undesirable to continue 
fumigation after the adults begin to emerge in considerable numbers 
in the spring. 'Plus time of emergence, of course, varies according to 
the locality and to weather conditions, but in general is between the 
middle oi' February and the first of March. It remains for further 
experiments to show bow far fumigation may be practiced with profit. 
at other seasons of the year. Tt is certain, however, that in cases of 
emergency, such as the checking of the spread of the fly in newly 
infested groves, fumigation can frequently be used to great advantage 
even in midsummer. 
M ET E< ) I : ( ) I .( )( ; I ( ! A I . EL E M E NTS . 
Light. -Fumigation is conducted in the absence of bright sunlight, 
to avoid injury to the foliage which may occur when this precaution is 
not observed. With tents treated with oil to make them nearly gas- 
tight, damage is almost certain to result from daylight fumigation. 
With untreated tents, however, the writer has on several occasions 
conducted fumigation experiments with the sun fifteen minutes high 
without appreciable injury to the foliage. One orange tree was 
fumigated forty minutes, beginning at 3 p. m., with the sun shining, 
without any shedding or burning of foliage resulting from the treat- 
ment . Tbc tent was placed over the tree twenty-five minutes before 
generating the gas, and at the beginning of the forty-minute period 
the temperature was 79.5° F., or 4.5° higher than the outside tempera- 
ture. Twenty and one-half ounces of potassium cyanid were used, 
and 97.7 per cent of the white fly pupae were destroyed. This amount 
of cyanid was 4\ ounces less than the amount called for by the 
table given in the Appendix. At the time of fumigation, the foliage 
on the tree was very much curled by drought and after a few rains 
became normal in appearance without the shedding of a single leaf. 
The leaves, at the time of the treatment, when torn seemed to be as 
dry as paper, alt bough many pupae of the white fly on neighboring 
tree- in a similar condition produced adults, as did the nine speci- 
men- which were known to survive on the fumigated tree. It is 
probable that Future experience will show that trees whose foliage is 
curled as a result of drought are not nearly so liable to injury by 
daylighl fumigation as are trees whose foliage is in perfect condition. 
Fumigation can safely begin with sundown, or, during the fumigat- 
ing season in Florida, between \ and 5 o'clock p. in. On dark, cloudy 
days fumigation scemsentirely safe at any time with untreated tents. 
