46 ANNUAL REPORTS OF DEPARTMENT OF AGRI< CULTURE, ' 
until the spring of L939, when extensive field tests of this bait were 
conducted in Washington, Nevada, Wyoming, and South Dakota. 
These field applications resulted in the destruction of from 7 s to '- ,s 
percent of tne crickets. They demonstrated conclusively the effec- 
tiveness of this bait when distributed at a rate not exceeding L2 
pounds i" the acre. It is believed that the genera] adoption of this 
means of control will result in a reduction in operating expense and 
an increase in safety to livestock within the affected are 
INSECTS ATTA< KIM. < ORN 
In 1938 a distinct genera] trend was observed toward increased 
populations of the European corn borer in a region extending from 
the Great Lakes eastward to Massachusetts and central Connecticut. 
( )f part icular significance in the ( treat Lakes area was the occurrenc ■ 
near Toledo, Ohio, of infestations averaging 17 borers per plant in 
early market sweet corn. This crop was severely injured in Lucas, 
Erie, and Huron Counties, Infestation rose rapidly in central New 
Jersey, particularly in Monmouth. Mercer, and Middlesex Counties, 
in part.- of which occurred the highest infestations in held corn that 
had as yet been recorded in this country. A maximum infestation of 
•j.:* borers per plant was observed in 4 percent of the fields examined. 
10 borers per plant in 21 percent, and 5 borers per plant in .">7 percent. 
In the breeding of -trains of sweet corn resistant to the corn borer 
398 inbred strains were tested at Toledo. Of these, 77 Golden 
Bantam. L2 Country Gentleman, and 4 Stowell Evergreen lines 
showed apparent resistance and were -elected for further testing. 
Among the Bantam inbred strain- tested in L938 were 25 inbred 
selections of sweet corn segregates of a cross of inbred lines 39D and 
a field corn inbred line R4. Only 1 of these line- was found to he 
significantly below average in performance, and 2 were significantly 
above average. 
In breeding field corn 82 of the 235 -trains tested in top-cross com- 
binations in 1938 were found to he resistant to the borer. Fifteen of 
these were tested both for first- and second-generation exposure. Of 
these, L3 carried their resistance through both generations, and only 
2 of them showed a slight degree of susceptibility to attack by the 
-rcoiid generat ion. 
The artificial distribution of the natural enemies of the European 
corn hoicr has progressed Steadily, and surveys made to determine 
the status of these parasites in 1938 in northwestern Ohio indicated 
that there ha- been a progressive increase in parasitization each year 
from L932 to L938, inclusive, of from <>.•_> percent in L932 to 20.9 per- 
cent during I he past year. 
An announcement was made in last year's report of the discovery 
oft wo practical method- of protecting ears of sw< et corn from attacks 
by the corn earworm. These methods are effective particularly for 
early market sweet corn and home garden purposes. One of them is 
the fumigation of the ear tip by inserting a -mall tablet of the chemi- 
cal hexachloroethane and subsequently applying a simple wire dip 
to prevent the gas from escaping after application. The other con- 
sists in the injection of a very small quantity of light mineral oil into 
the ear. These new method- are fully described and illustrated in 
two publications issued b) this Bureau, namely. The I -e of Oil for 
