10 BULLETIN 708, U. S. DEPARTMENT OF AGRICULTURE. 
large percentage of the protecting shucks would seem to be an 
insurmountable barrier to those who would breed for shuck protec- 
tion against weevils. It has been shown (Table V), however, that 
the proportion of ears attacked by worms tends to decrease as the | 
shuck extension is increased. 
The earworms usually enter the shuck coverings through the silk 
channels, feeding on the silk as they go, the holes through the shucks 
being made when they are leaving. If while feeding on the silks and 
with its hunger not yet satisfied a worm reaches an ear which is 
sufficiently tender to be attractive, it may feed upon the kernels and 
cob for a time before cutting out. If, however, during its progress 
along the silk channel the silks become unpalatable on account of 
age or the worm reaches maturity, it may abandon its course before 
reaching the ear. Reasoning along this line, one naturally concludes 
that the longer the shuck extension or silk channel the more likely 
it is that worms will leave the shucks before they reach the grain. 
This conclusion is supported by the data presented in Table VI. 
The ears examined for this information were a part of those examined 
to obtain the information given in Table V. 
TaBLe V1.—Relation of the length of shuck extension of ears of corn io the worm damage. 
: from silk 
examined. channels be- 
fore reaching 
the grain. 
Percentage 
oi ears not 
| Total num. |r besos 
"Kind of shuck covering. | ber ofears | rom silk 
Exiend ding 4 4io 6 inches he yond tips oh@arss: 22. Sea ee ee ee iii 
_Exiending 2 to 3 inches beyond tips of ears... ...=.-=._----.----------------- 102 
Advantage due to the longer shuck extension__....._....._...---..---- ooo eee 7 
It may be seen that of the 111 ears with shucks extending from 4 
to 6 inches beyond the tips of the ears, 14 per cent had escaped 
damage because the worms had cut from the silk channels before 
reaching them. It may also be seen that of the 102 ears with shucks 
extending from 2 to 3 inches beyond the tips of the ears, 7 per cent 
had esc -aped damage because the worms had cut from the silk channels 
before reaching them. 
By comparison it may be seen that the longer shuck extension 
afforded 7 per cent more protection than the shorter shuck extension. 
These investigations, in part at least, show why shuck extension 
reduces the amount of worm damage. In addition, they suggest the 
possibility of breeding a shuck extension long enough to be entirely 
effective against earworms. The extent to which the earworms can 
be eliminated by the means suggested can only be determined by 
other investigations. 
a4) 
SN 
