10 



BULLETIN 708, U, S. DEPARTMENT OF AGRICULTUEE. 



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. Keasoning 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 VI. — Relation of the length of shuck extension of ears of corn to the ivorm damage. 



Kind of shuck covering. 



Total num- 

 ber of ears 

 examined. 



Percentage 

 of ears not 

 eaten because 

 worms cut 

 from silk 

 channels be- 

 fore reaching 

 the grain. 



Extending 4 to 6 inches beyond tips of ears. 

 Extending 2 to 3 inches beyond tips of ears. 



m 



102 



Advantage due to the longer shuck extension. 



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 escaped 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. Tlie extent to which the eanvorms can 

 be eliminated by the means suggested can only be determined by 

 other investigations. 



