HABITS OF THE LARVA. 
25 
As an illustration of how abundant this insect may become, the 
following observations are given: On August 31, 1909, Mr. Foster, 
of this bureau, found it severely infesting pear foliage at Martinez, 
CaL, and noted as many as 200 larvae on one side of a leaf. On 
July 28, 1910, the writer found some plants of spiny lettuce badly 
infested by the larvae of this thrips, and 10 leaves gave a total infes- 
tation of 733. ( See Table III. ) 
leaf. 
This gave an average of 73.3 to each 
Table III. — Infestation of Lactuca scariola by larvae of the bean thrips. 
No. of 
leaf. 
Number 
of larvae 
on under 
side. 
Number 
of larvae 
on nnper 
side. 
Total 
number of 
larvae 
on leaf. 
No. of 
leaf. 
Number 
of larvae 
on under 
side. 
Number 
of larvae 
on upper, 
side. 
Total 
number 
of larvae 
on leaf. 
1 
2 
3 
4 
5 
6 
70 
34 
43 
30 
59 
46 
7 
39 
2 
2 
47 
46 
77 
73 
45 
32 
106 
92 
7 
8 
9 
10 
44 
61 
70 
23 
47 
30 
1 
32 
91 
91 
71 
55 
480 
253 
733 
On July 18, 1911, at Hollywood, CaL, leaves of spiny lettuce were 
found that had several hundred larvae to a leaf. September 22, 1910, 
Mr. AVildermuth observed a field of cotton at El Centro, CaL, show- 
ing considerable injury by this insect, and counted as many as 200 
larvae to a single leaf. 
MOLTING. 
The larva molts once, giving two larval instars, then molts to the 
prepupal stage. On July 28, 1910, a number of larvae that had just 
hatched were separated and on August 2 these all molted. On August 
7 they again molted and changed to prepupae. This gave the first 
instar a length of five days and the second a length of five days. The 
process of molting in the larva is continued unprotected in the midst 
of the feeding colony. After molting the skin is left adhering to the 
leaf beside the feeding larva. 
It was observed with the larvae of this species and of those of the 
greenhouse thrips that when they were exposed to a low temperature 
the entire development was checked and growth remained stationary 
during the exposure. In long-continued exposures the insects were 
killed, but if within three weeks they were again removed to higher 
temperatures the larvae resumed their growth and pupated in a 
few days. 
Under the artificial conditions of rearing in vials the mature 
larvae seek concealment before pupation in curled-up leaves, in all 
kinds of protected places, and if in vials closed with cotton plugs 
they work their way in between the plug and side of the vial. In 
the field, however, the larvae when full grown desert the plants and 
hide in rubbish and cracks in the ground or beneath clods of earth. 
51097°— Bull. 118—12 4 
