4 
The so-called pupal stage, up to the time when growth ceases, is in 
reality the fourth larval stage, the fourth larval skin enveloping the 
true pupa. The pup and empty pupa skins are quite conspicuous 
when the insects are abundant. Their outline is similar to that of the 
larvee, but they are thicker and box-like, about three-fourths of a mil- 
limeter, or three-hundredths of an inch,in length and provided with 
long, slender wax rods or secretions which are useful in distinguishing 
this from nearly allied species of the white fly. 
The entire stage from the insect’s third molt to the emergence of 
the adult form lasts from twelve to sixteen days in the laboratory and 
greenhouse. The adult emerges from a T-like opening, leaving the 
glistening white pupa case attached to the leaf. At first the wings of 
the adult are crumpled close to the body, giving them a peculiar 
appearance. In the course of a few hours the wings unfold and the 
insect has then completed its development, which has extended over 
nearly five weeks, if under the ordinary temperature conditions of a 
greenhouse. 
CLOSELY RELATED FORMS. 
In addition to the one here discussed, there are but two other species 
of white flies which are likely to be met with in the greenhouse. A 
white fly found infesting citrus plants would be likely to be the 
orange white fly (Aleyrodes citri Riley and Howard), while one infest- 
ing strawberry plants, either in the greenhouse or in the field, would 
probably prove to be the strawberry white fly (Aleyrodes packardi 
Morl.). The latter species resembles the one commonly found in green- 
houses, but fortunately its list of food plants is much more restricted, 
it being apparently unable to subsist on the tomato. 
APPEARANCE OF INFESTED PLANTS. 
As already stated, the upper leaves of a plant are preferred by the 
adult females for the deposition of their eggs. Thus there is a slow but 
continuous migration of adults upward to keep pace with the unfolding 
of the leaf buds. On thoroughly infested plants we find on the upper- 
most leaves only adults and freshly laid eggs; a little lower on the 
plants we find eggs in the process of hatching; and, finally, on the 
lowermost parts of the plants we find discolored, shriveled leaves with 
many pupee and emerging adults and few, if any, unhatched eggs or 
young larve. The larve and pupe secrete little globules of honey- 
dew, so named after the material of a like nature secreted by plant 
lice. ‘These globules usually either drop or are forcibly ejected, and, 
falling on the upper surface of leaves directly below, give them a 
glazed appearance. This is frequently followed by the growth of a 
sooty fungus which hastens the complete destruction of the leaf. 
When overcrowding of the young occurs, this fungus growth finds 
favorable conditions for its development on the under surface of the 
