14 THE REPORT OF THE No. 36 



in single or double layers, infested stalks containing an unknown number of 

 larvae, at a uniform depth of six inches, in variety of soils; as well as of other 

 series of experiments by ploughing down the undisturbed crop refuse of stubble 

 and stalk in a field from which the crop had been cut and which was known to 

 have been severely infested. This material contained large numbers of larvae. 

 Traps were placed on the soil surface surrounding the material thus disposed 

 of for the recovery of the caterpillars. About the burials, the traps were arranged 

 to recover larvae only on the inner side, while on the ploughed areas they were 

 designed to capture the larvae wandering about the surface on both the inner 

 and the outer sides. These recovery traps were constructed to present to the 

 wandering larvae a suitable place in which to spin up for the winter, where the 

 larvae, thus taken, would be easily available for daily examination and removal. 

 A description of this trap will appear in the Canadian Entomologist for 1923. 



Of the studies carried on between 1920 and 1922, the series of ploughings 

 in the fall of 1922 most directly bear upon and illustrate the conditions to be 

 met with in the field. This paper thus takes the form of a progress report and 

 deals with the autumn activities of the corn borer larvae ploughed down with 

 the crop refuse left in the field after a severely infested crop had been harvested 

 in the regular manner, that is, to say, with the binder cutting the corn at a height 

 of approximately six inches. 



The study was carried on at Dexter, Ontario, upon the eastern edge of the 

 area of most severe infestation in 1921. It consisted of a four acre sand loam 

 field, planted on May 27th, 1922, to smut-nose, white and yellow Flint corn in 

 hills 3' 6" square. By the end of the season it had sustained a stalk infestation 

 of 100 per cent, and a farm loss of 40 per cent. The crop was cut early in Septem- 

 ber and the stalks stooked in the field throughout most of the fall experiments. 

 The larvae under study were those normally present in the stubble and pieces 

 of broken stalk left by the crop. The ploughing was done with an ordinary 

 single furrow walking plough and skimmer about seven inches deep in strips 

 about fifteen feet wide running north and south, at intervals across the field, 

 of from 35-42 feet. The ploughings began on September 28th and were carried 

 out at weekly intervals till November 9th. The work was done very carefully, 

 and though there was present an average of 18.29 feet of stalk and 20 stubble 

 per 36.75 square feet of surface, the surface of the ground was exceedingly clean. 

 It was with difficulty that 25 feet of refuse for study was found on the surface 

 of 1/10 of an acre. In 1921 a similar field, ploughed between September 19th 

 and 24th and seeded to wheat, had practically all the larvae leave the material 

 below ground and come to the surface before the freeze-up in November. Hence, 

 in 1922, it was of particular interest to determine the reaction under the later 

 fall conditions. 



Seven ploughings were made, one upon each of the respective dates; Septem- 

 ber 28, October 6, 12, 19, 26, November 2, and November 9, each strip involving 

 the space between a row of stooks. 



On top of each ploughed strip a two-way recovery trap 8 feet square was 

 placed, enclosing 64 square feet and supposed to surround nine hills of stubble 

 and the associated refuse. The traps were placed in position immediately after 

 the ploughing and were looked at daily, in the early morning until the nights 

 became frosty, after which time the recording was done later in the day. 



The narrowness of the ploughed strip resulted in that the east and west 

 outer sides of the trap were not as favourably situated for recovering larvae 

 in numbers as the other two sides and hence cannot be used in attempting to 

 determine the direction of migration. The numbers recovered on the inside of 



