5) 
leaf, resulting in the destruction of many of the immature insects. 
Owing to the interference with the respiratory processes of the leaf, 
both by the bodies of the insects themselves and by the fungus growths 
due to them, badly infested plants have a tendency to wilt when exposed 
to the sun’s rays. In seriously infested greenhouses the leaves of the 
plants gradually die, the lower leaves first, and if unchecked the insects 
greatly impair the value and vitality of the plants, even though they 
do not actually cause their total destruction. 
PREVENTIVES. 
The importance of preventive measures in combating the white fly 
in greenhouses is not due to the inefficiency of properly applied reme- 
dies, but to the fact that in many cases the tiny depredator is unob- 
served until considerable injury has been accomplished. With little 
trouble and expense one may, in a large measure, preclude the possi- 
bility of this and other pests appearing in the winter in greenhouses 
which are unused during the summer months. The introduction of 
the insect into noninfested floral establishments may be prevented by 
avoiding the introduction of infested plants unless first subjecting 
them toa fumigation ina tight fumigating box, based on the directions 
hereafter given for entire greenhouses. Vegetable houses, which are 
not used during the summer months, allow of a practice which not only 
greatly reduces the chances of the white fly appearing in the house 
during the growing season, but may result in the house being success- 
fully kept free from thrips and other insect pests during the whole ora 
considerable part of the season. The practice referred to consists in 
removing from the house all vegetation, even the smallest weeds, and 
fumigating the tightly closed greenhouse with hydrocyanic-acid gas at 
the rate of 5 or more ounces per thousand cubic feet of space for a ten 
hours’ exposure. 
REMEDIES. 
Fumigation with hydrocyanic-acid gas.—This has been found to 
be the most successful means of controlling the white fly in green- 
houses. Its success in this case is due to the susceptibility of the 
adults and larve of these insects to a comparatively long exposure to 
a small amount of the gas. Many experiments have been conducted 
with a view to determining the usefulness of this gas against the 
greenhouse white fly, the amount of gas to be generated, and the 
length of exposure necessary to produce the best results.“ Experi- 
ments of this kind thus far have been with tomato and cucumber 
plants, but as these plants are among those most liable to injury from 
improper fumigation with hydrocyanic-acid gas, a wide range of use- 
fulness is indicated by the success thus far obtained. 
@Conn. Station Bul., No. 140; New Hampshire Station Bul., No. 100; Mass. Station 
Tech. Bul., No.1; Maine Station Bul., No. 96; Can. Entomologist, XXXVI, p. 35; 
American Gardening, XIX, p. 741. 
