INSECT ENEJVIIES — PACKAUD 666 



furrows or strips across the line of march of the bugs, in which a deep, 

 dusty mulch was produced by continuous dragging of a log back and 

 forth in the furrows, or by harrowing the strips. The dust and the 

 dragging or harrowing together effectually prevent the bugs from 

 getting across such barriers in injurious numbers. This type of bar- 

 rier, however, has two serious disadvantages : The continuous attention 

 it requires, and the impossibility of maintaining it in wet weather. 



The barrier idea has been utilized in a much different way in the 

 control of the corn earworm (pi. 17). As many people know who 

 have raised sweet corn or have husked ears preparatory to cooking, 

 these greenish or brownish worms eat their way down through the 

 tip of the ear and the kernels, making very messy burrows and giv- 

 ing the ears an extremely unattractive appearance. After much 

 study of the insect's habits and experiments with various methods 

 of control, Dr. George W. Barber finally developed a barrier method 

 which prevents the worms from entering the ears. He found that 

 the injection of about 14 teaspoonful of refined mineral oil into the 

 silk mass at the tip of the ear creates an effective barrier against 

 the entrance of the little newly-hatched worms, emerging from the 

 minute eggs laid by the parent moths on the silks, and their subsequent 

 injury to the silk mass and the kernels. Barber also discovered, 

 however, that the oil interferes with the pollination and filling out 

 of the kernels if injected too soon after the appearance of the silks; 

 hence it is necessary to wait 3 or 4 days until the wilting of the silks 

 indicates that pollination is complete. He observed that during this 

 interval some worms succeeded in penetrating well down into the 

 ear tip, and realized the need of some improvement of the method. 

 Further work revealed the fact that a very small percentage of py- 

 rethrum extract or dichloroethyl ether added to the oil killed most of 

 the worms that had entered the ears before treatment as well as 

 those that entered them afterwards. In the course of his studies 

 Barber also devised simple adaptations of common equipment to the 

 application of the oil easily and economically (pi. 17). This method 

 has also been used with some success for the prevention of earworm 

 injury to the highly valuable plantings of pedigreed lines of corn now 

 grown for the production of the high-yielding hybrid field and sweet 

 corns that have almost entirely supplanted the open-pollinated va- 

 rieties. 



Before a successful poison bait for the Mormon cricket was dis- 

 covered galvanized sheet-iron barriers were widely used in the con- 

 trol of this insect (pi. 11). Long strips 10 inches wide were fastened 

 upright and end-to-end by means of small stakes, across the path 

 of the migrating bands of crickets. Trap pits, or enclosures made 

 of the galvanized-iron strips, were located at frequent intervals 

 along the barrier. In these the crickets gathered and died. Many 



