124 VEGETABLE FORCING 
low temperature and poor food are unfavorable to egg 
production, and suitable conditions maintained in the 
greenhouse for plants requiring high temperatures are 
favorable for the rapid multiplication of this pest. The 
incubation period ranges from three to eight days, the 
length depending on temperature. All of the eggs noted 
by Ewing hatched, unless the temperature was too low 
or they were destroyed by predaceous insects. The 
spider mite is parthenogenetic; that is, fertilization is 
not necessary in order that the eggs may hatch. 
The new almost flesh-colored larva begins to feed soon 
after it is hatched, and remains near the plant where it 
emerged from the shell. While the larva does not spin 
a web it is frequently found on webs spun by adults. A 
trifle more than three days is the average period of the 
larva stage, and about the same time is required to pass 
the first nymph stage, when the mites are also active 
feeders. The second nymphs have the ability to spin 
webs, and the duration of this period is practically the 
same as for the first stage. There is an active and a 
quiescent period in each of the three stages explained. 
The average duration of the adult stage is over 21 days, 
and eggs are laid throughout the period, except about the 
first five days. 
The eggs are nearly spherical, covered with a tough 
shell, pearly in appearance and 0.09 millimeter in size. 
They are deposited singly, but generally close together. 
The larva is almost spherical, flesh-colored and has but 
six legs. It averages 0.19 millimeter in length. The 
first nymph is very similar to the larva, except that it 
possesses an extra pair of legs and is larger, being 0.27 
millimeter in length. The second nymph is very similiar 
in shape to the first, but averages 0.36 millimeter in 
length. 
The adults vary greatly in color. They may be green, 
yellowish, greenish yellow or bright orange. Females 
average 0.42 millimeter in length and the males 0.32 
