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 



