Recent Experiments With Thrips on Citrus 
J. R. Watson, Gainesville 
Thrips injure citrus in two ways, (i) 
their feeding and egg punctures cause con¬ 
siderable of the fruit to drop. This would 
be more serious if the citrus tree did not 
normally bloom so profusely that a large 
proportion of the fruit must necessarily 
drop. 
(2) Their feeding punctures on the 
young ovary result in shallow injuries 
which develop into scars that mar the ap¬ 
pearance of the fruit and lower its grade. 
The work during the two years just past 
has had more to do with the latter type of 
injury, namely, the scarring of the fruit. 
The scars produced by thrips are very 
characteristic and need not be confused 
with those produced by other causes, al¬ 
though, of course, they may be compli¬ 
cated by the latter. They differ from scab 
in being sunken rather than raised, but 
are not as deeply sunken as those resulting 
from the feeding of grasshoppers and 
katydids. They differ from melanose and 
mechanical injury including rubbing 
against twigs or leaves in that they are 
smooth and shining rather than rough, as 
well as in their peculiar irregular shape. 
Oranges are much more severely in¬ 
jured than grapefruit. Thrips are not 
present in numbers in the trees until the 
bloom begins to open. They then fly into 
the trees, mostly from other blossoms, es¬ 
pecially weeds. In the flowers they feed 
mostly on the bases of the petals and sta¬ 
mens. They are sucking insects but their 
mouth parts are very short, only a frac¬ 
tion of a millimeter, less than a hundredth 
of an inch, and consequently their punc¬ 
tures are very shallow but numerous and 
placed close together. 
Attacked stamens and petals turn brown 
in spots and fall prematurely. Eggs are 
never laid in the petals or stamens but al¬ 
ways in the receptacle, the enlargement of 
the stem to which the fruit is attached. 
They are laid in shallow slits just beneath 
the epidermis of the plant. They hatch in 
three or four days and the young at once 
crawl into the blossom or onto the young 
fruit. The scarring of the fruit seems to 
be caused mostly by these young thrips of 
the second generation. As soon as the 
petals and stamens drop, the winged adults 
practically all leave and fly to other blos¬ 
soms ; but the young which have no wings 
remain and feed on the young fruit. 
However, they do often crawl from the 
receptacle on which they were hatched to 
neighboring freshly opened blossoms. 
But even in fresh blooms they collect 
largely at the base of the ovaries. Their 
