14 
BULLETIN 616, U. S. DEPARTMENT OF AGRICULTURE. 
and from the latter part of September to November it will range 
from about 12 to 14 days. 
Table IV. — Seasonal variations in duration of the larval stage of the citrus 
thrips, Lindsay, Cal, 1911. 
Period of season. 
Prevailing 
tempera- 
tures. 
Mar. 25 to Apr. 15 
May 13 to June 3 . 
June 13 to Sept. 5. 
Sept. 4 to Sept. 21 
Sept. 23 to Nov. 5 
o K 
59.62 
62.58 
74.61 
67.47 
58.48 
All four molts of the citrus thrips, comprising two in the larval 
stage and two in the pupal stage, are accomplished in about the same 
manner. The first molt takes place on the leaves and fruit of the 
host plant, the remainder in some secure hiding place, usually on the 
ground. When ready to molt the larva ceases to feed and becomes 
inactive. Tremors vibrate the antennae and body at brief intervals 
for a period of from one to three hours, and the abdomen slowly con- 
tracts and shrinks away from the old skin. Then follows an active 
period of from 15 minutes to an hour, in which the middle and hind 
legs are repeatedly stretched as far back as possible and slowly 
drawn forward, while the insect goes through jerky lateral motions 
with the body. The skin then splits from the vertex along the 
dorsum to the abdomen, after which the insect becomes very active, 
doubling down with the head between the fore feet and slowly re- 
moving the skin from the head and antennas. The legs are then 
worked out of their casings and the exuvium pushed back under the 
body. The skin usually is attached at the tip of the abdomen to the 
surface on which molting occurs, greatly aiding the insect in ex- 
tricating itself. The skin generally is removed entire, but occa- 
sionally antennal and leg casings are removed separately. Cool 
weather greatly retards the process, which is more likely to be ob- 
served when such weather prevails. Groups of larval skins re- 
sembling specks of gray dust sometimes are found on orange leaves. 
The molting process in the citrus thrips is similar to that observed 
in certain Orthoptera. 
THE PUPA. 
DESCRIPTION. 
The propupa, — The propupa, or first instar (fig. 6), is very similar 
in general appearance to the larva. It is generally somewhat paler 
