INSECT ENEMIES AND THEIR CONTROL 121 



eggs deposited per day by an adult female white fly in a laboratory 

 has been found to average very nearly four. Probably in the warmer 

 temperature of a greenhouse this number is greater by one or two 

 eggs per day. These observations, even though falling short of 

 showing the normal increase in numbers of this species, emphasize 

 the importance of a remedy which will, above all, destroy the adults 

 and check at once the rapid deposition of eggs. A peculiarity of 

 the egg-laying habits of this and some other species of white fly is 

 the tendency to deposit the eggs in a circle while feeding, using the 

 beak as a pivot. These circles, when completed, are about \ l / 2 mm. 

 in diameter and usually contain from 10 to 20 eggs each. On the 

 more hairy leaves groups of eggs of this kind are less frequently 

 met with than on those which are more nearly smooth. The ma- 

 jority of the adults are found upon the upper and newer leaves of 

 the food plant. They are almost invariably found upon the under- 

 side of the leaves, and it is here that nearly all the eggs are de- 

 posited, although many are found upon the tender stems and leaf 

 petioles and a very few scattering ones on the upper surfaces of 

 the leaves. 



"The eggs are distinguishable with difficulty by the naked eye, 

 being but one-fifth of a millimeter, or one one hundred and twenty- 

 fifth of an inch, in length. They are more or less ovoid in form 

 and suspended from the leaf by a short, slender stalk. With ordinary 

 greenhouse temperatures the eggs hatch in from 10 to 12 days. The 

 newly hatched insect is flat, oval in outline, and provided with ac- 

 tive legs and antennae. It rarely crawls farther than one-half inch 

 from the empty eggshell before settling down and inserting into the 

 tissue of the leaf its threadlike beak. After feeding for five or six 

 clays, the insect is ready to molt its skin. The second and third 

 stages are much alike, except in size, and differ principally from the 

 first stage in that the legs and antennae are vestigial and apparently 

 functionless. These two stages occupy from four to six days each. 



"The so-called pupal stage, up to the time when growth ceases, 

 is in reality the fourth larval stage, the fourth larval skin envelop- 

 ing the true pupa. The pupae and empty pupa skins are quite con- 

 spicuous when the insects are abundant. Their outline is similar 

 to that of the larvae, but they are thicker and boxlike, about three- 

 fourths of a millimeter, or three hundredths of an inch in length, 

 and provided with long, slender wax rods or secretions which are 



