16 BULLETIN 616, U. S. DEPARTMENT OF AGRICULTURE. 
of predatory insects than any other stage, and therefore pupation 
occurs in places practically inaccessible to any but the smallest in- 
sects and mites. The pupae are scattered widely, thus limiting the 
possibility that any great number will be destroyed at one stroke. 
They have been found in the following situations: On the ground 
under the trees; in curled, dried leaves, and under a mat of fine 
cobweb and dust on dry leaves; in the split tips of leaf stems; in 
small crevices in the bark of dry twigs. In clean-cultivated young 
orchards, where but few dead leaves and twigs collect, the thrips 
pupate in crevices near the base of the trunks, under dead and living- 
fluted scales {I eery a purchasi Mask.), and in similar obscure situa- 
tions. In only two instances was pupation found to have occurred on 
the upper part of the tree : One in which a propupa was found in a 
distorted leaf, and another in which one specimen occurred under the 
cocoon of a caterpillar on an orange leaf. To find pupae of the citrus 
thrips requires a minute and painstaking search. If no better shelter 
offers, the insect gathers particles of dust, wood, leaves, etc., about 
itself, effectively concealing it. In captivity a large proportion of the 
pupating specimens crawled into the cotton plugs of the rearing 
bottles and under the split bark at the ends of orange stems used 
as food. No food is taken during the pupal stage. 
DTJKATION OF THE PUPAL STAGE. 
The duration of the pupal instars may be accurately determined, 
as once a spot has been chosen for pupation the insect seldom moves 
from it, and cast skins of the last larval and both pupal transforma- 
tions generally remain nearby. The first pupal instar ranged from 
1 to 9 days, with an average for the entire active season, from April 1 
to November 8, of approximately 2 days. The second instar ranged 
from 1 to 25 days, with an average of 5.5 days for the period from 
April 4 to December 2. The 25-day maximum period is of course 
exceptional, and would occur in comparatively few individuals of 
very late hatch. 
The entire variation in duration of the complete pupal stage in 
the period from April 1 to December 2 was from 2 to 28 days, with 
an average of 7.5 days. The important general variations in the 
length of the pupal stage in different periods of the season are 
shown in Table V. It will be seen that growth of the pupa, as well 
as of the egg and the larva, is slow in the cool weather of spring and 
fall, when the temperature ranges between 50° and 60° F., and 
that it is considerably accelerated in midsummer, with temperatures 
above 60° F. * 
