February, ’24] 
CRAWFORD: PLOWING FOR CORN BORER 
135 
and none took place till the spring of 1922. In the spring the larvae 
began to come to the surface during the first week of May and by the 
end of May practically all the larvae had left the buried stalks. (See 
Tabulation No. 1, Sect. 4). 
The soils in which the stalks were buried seemed to have a definite 
influence upon the rate at which the larvae left the stalks. The observa¬ 
tions showed that they left most readily from wet sand-loam and with 
decreasing readiness from dry sand-loam, wet clay, sand, and dry clay 
in the order mentioned. It was also noted that where stalks were buried 
in single layers they were relatively very retentive of larvae. Larvae 
were likely to be retained for a longer time in the soil surrounding the 
burial in sand than in dry sand-loam which in turn retains them longer 
than wet sand-loam. The clays were too difficult to handle to get 
exact counts upon this point. In general, apart from the possible 
mechanical difficulty in leaving the stalks in certain soils, the rule seems 
to be that anything which promotes increased moisture in the buried 
stalks tends to hasten the departure of the larvae from materials below 
ground. 
Tabulation No. 1 will give some idea of the progressive reduction of 
larvae in the material underground at various time intervals after burial 
in representative experiments throughout this type of study. 
Effect of Ploughing Upon the Larval Population 
The studies in actual ploughing included the turning under of standing 
sweet corn in August, the ploughing down of normal, infested crop 
refuse in September 1921, a series of ploughings at weekly intervals 
begun in late September, 1922 (reported upon in a previous study), 
and finally a series of ploughings at weekly intervals in the spring of 1923. 
In studying the effect of the ploughing upon the larval population, 
the recovery of the larvae at the surface above the ground was stressed 
and by this daily record the exact rate at which the larvae left the 
buried stalks and stubble and came to the surface under ordinary 
agricultural practice was determined. These records were secured by 
establishing an 8 foot two way recovery trap upon each piece of ground 
immediately after ploughing and keeping it in position throughout the 
season. In the case of the fall ploughings the traps were taken up in 
the fall, the surface of the land was not disturbed in the spring and 
the traps were put down again on April 27th of the following year. 
At the end of each experimental season the stalks below the soil within 
the trap were measured and the stubble and larvae counted and com- 
