16 
BULLETIN 640, U. S. DEPARTMENT OF AGRICULTURE. 
the fruit fly can not mature in them. The milky juice, which exudes 
copiously from breaks in the skin of the fruits up to the time when 
the fruits can be cut 
for ripening in the 
house, contains a di- 
gestive principle that 
is fatal to the eggs 
and larvae of the fly. 
This juice protects 
the fruits from infes- 
tation when imma- 
ture. But as the 
fruits become over- 
ripe, and also unfit 
for the table, the juice 
flows less abundantly 
from breaks in the 
skin made by the fly 
when she attempts to 
lay her eggs, and the 
eggs which she then 
lays can mature. As 
many as 205 flies have 
been reared from sin- 
gle overripe fruits. 
So while the papaya 
is a host fruit, it is 
practically never in- 
fested until too ripe 
or otherwise unfit for 
the table. 
AVOCADOS. 
With the exception 
of one or two early 
varieties, the infesta- 
tion of the avocado 
is so obscure that the 
general belief prevails 
in Honolulu that this 
fruit is free from at- 
tack. The Guate- 
mala, or nutmeg, variety is the only one free from attack when growing 
uninjured. Theskinof allothervarieties, whether thin or of usual tough- 
ness, canbe punctured by the adult fly, as proved by many examinations 
of fruits. The avocado, like the ordinary pear, is best when picked 
Fig. 13.— Avocado. This valuable fruit of California and Florida is 
subject to infestation in Hawaii. In this instance the maggots are 
working at the stem and blossom ends. (Authors' illustration.) 
