February, ’24] 
CRAWFORD: PLOWING FOR CORN BORER 
139 
night following the ploughing and continued to be taken as long as the 
temperature of the soil continued to attain a temperature of about 50 F. 
for some part of the day, which is well after frost. As great a proportion 
as 8.03% of the total recoveries were secured between November 10th 
and November 21st. At the end of the experiment, studies were made 
in the material below ground and it was very clearly evident that the date 
of ploughing was a most important consideration. Thus the following 
percentages of the larval population came to the surface following the 
operations upon the respective datesSeptember 28th, 85.36%; Oc¬ 
tober 6th, 61.36%; October 12th, 67.53%; October 19th, 29.87%; 
October 26th, 12.5%; November 2nd, 10.00%; November 9th, 12.5%. 
As the cool weather was approached the rate of emergence decreased, 
smaller proportions of the recoveries being made in the first weeks of 
the experiments. Warm spells were accompanied by increased recoveries 
and cold spells by a falling off in numbers until late November when they 
ceased altogether. The cages were taken up in the fall and were replaced 
again upon 5 of the experiments a few days after the frost went out of 
the ground in the following spring. The balance of the larvae which 
had failed to come to the surface in the fall came up in the spring. 
The movement upward began on April 29th and continued throughout 
the spring until June 8th, the bulk of them coming up in the first three 
weeks of May, and by June 12th when the material below ground was 
examined no live larvae were found. 
Five serial spring ploughings were carried on in 1923 in the unploughed 
parts of the same field as the fall studies of 1922. These experiments 
consisted of ploughing down the normal refuse at intervals of a week, 
beginning April 23rd and recovering the larvae when they came to the 
surface in the same way as from earlier ploughings. The day following 
the first ploughing, April 24th, the larvae began to come to the surface 
and continued to come up until June 7th. Where the ploughing was 
done later in the season the larvae came to the surface much more 
promptly than in the earlier experiments, associated doubtless with the 
higher temperatures of the soil. By the 12th of June practically every 
larva had left the buried material but 4 larvae being recovered below 
ground in the five spring ploughing experiments. From the combined 
fall and spring ploughings (9) examined on June 12th with a calculated 
expectation of 427 larvae but 4 were secured below ground and 330 
larvae had come to the surface and were recovered upon the inside of the 
traps. This practically amounts to a complete elimination of the larvae 
