THE CITRUS WHITE ELY: LIFE HISTORY AND HABITS. 53 
A very satisfactory method of definitely marking larvae in order 
that no mistake may be made in identifying field notes with the 
individual larva? to which they refer, is to scratch lightly on the 
epidermis of the leaf, with a thorn or pin, a bracket or other mark 
and outside this a number that shall correspond with that used in 
the note book. In marking larvae care should be taken in scratching 
the leaf to allow for the future growth of the insect and not to injure 
the epidermis of the leaf too severely. In this manner a large number 
of larvae were marked as soon as they settled and their growth noted 
by daily observations. 
In determining the sums of effective temperature, 43° F. has been 
taken as a basis in accordance with Dr. Merriam's general law 
although this has led to certain inaccuracies of which the authors 
are aware. The determination of the effective 
temperature in the case of the white fly would 
require a special study which it has been imprac- 
ticable to undertake. 
The Egg. 
description. 
The eggs of the citrus white fly (fig. 3) are so 
small that they appear to the unaided eye as 
fine particles of whitish dust on the under sur- 
face of the leaves. Their minute size is empha- 
sized by the fact that 118 placed end to end would measure but an 
inch, while about 35,164 could be placed side by side in one square 
inch. Under the magnifying lens they appear as smooth, polished, 
greenish-yellow objects shaped much like a kernel of wheat. Fol- 
lowing is a more minute description: 
Length, 0.2-0.23 mm.; width, 0.08-0.09 mm. Surface highly polished, without 
sculpturing, color pale yellow with faint greenish tinge when first deposited, paler than 
the under surface of the leaf. Egg elongate, subellipsoid, slightly wider beyond the 
middle or at about the point where the eyes of the embryo subsequently appear; borne 
at end of a comparatively slender brownish petiole or footstalk, slightly shorter than 
the width of the egg, and somewhat knobbed at base. 
As the embroyo approaches maturity its purple eyes may be seen 
showing distinctly through the egg membranes at a point beyond the 
middle of the egg. At about this time, also, the hitherto uniformly 
colored egg contents become orange or golden at the proximal end and 
whitish translucent on the distal three-fourths. The egg surface 
sometimes assumes a white pruinose appearance, due to the presence 
of wax rubbed from the bodies of the adults while crawling over the 
eggs. Eggs deposited on leaves from which the adults have been 
excluded after egg deposition do not show this pruinose condition. 
Fig. 3. — The citrus white 
fly (Aleyrodes citri): Eggs. 
G reatl y enlarged . ( r igi- 
nal.) 
