THE CITRUS THRIPS. 25 
are deposited, and thus it occasionally happens that a considerable 
number of the eggs are frozen. In the winter of 1911-12 more or less 
severe freezing occurred throughout the citrus-growing sections of the 
State. The leaves and stems of the principal summer's growth were 
browned and withered, and the thrips suffered a considerable reduc- 
tion in numbers in many orchards. For example, an orchard which 
had been severely infested by thrips during the three years from 1909 
to 1911, inclusive, and particularly in 1911, when the entire crop was 
rejected because of thrips scabbing, was frosted so badly during the 
winter of 1911-12 that the tender leaves and stems were wilted and 
blackened well clown into the leaf expanse of the trees. In August, 
1912, examination of the fruit from this orchard showed only 13 
per cent of it to be marked by thrips, the degree of injury being noted 
at the time as mostly very slight stem-end rings. Thrips were very 
scarce and the leaves showed little injury except in scattered spots. 
RAINS. 
From the fact that rains are supposed to be a powerful agency in 
the natural control of some species of thrips, it has been argued that 
a season of unusually heavy rainfall would reduce greatly the number 
of citrus thrips. Whatever merit rainfall may have in checking 
thrips of other species, its effect on the citrus thrips under the con- 
ditions prevailing in the San Joaquin Valley and in Arizona could 
not be of the least importance, since the heavier rains do not begin 
there until October at the earliest, and usually not before November 
or December, by which time almost all the overwintering eggs have 
been deposited. In spring the rains cease before the thrips emerge 
in any considerable number. The season of 1909, following the 
heaviest rainfall in the three-year period from 1909 to 1911, inclusive, 
in the San Joaquin Valley, was the worst season for thrips injury 
on record. 
NATURAL ENEMIES. 
INSECTS. 
The most important insect enemy of the citrus thrips is the larva 
of the common lacewing fly of California (Ohrysopa calif omica 
Coq.) - 1 In its early stages this larva feeds largely upon larvae of the 
citrus thrips. In October, 1911, an examination of 10 one-year-old 
orange trees on which thrips were numerous disclosed an average of 
25 eggs of this Chrysopa per tree. A number of the sickle- jawed 
larvae were also present in the trees, and several of the smaller ones 
were engaged busily in feeding upon thrips. The thrips were indeed 
almost the only food available to the lacewings in quantity on these 
1 Identified by Nathan Banks. 
