1923 



ENTOMOLOGICAL SOCIETY. 



17 



A general survey of some other experimental results bearing upon the prob- 

 able behaviour of the larvae when moving from a given experimental concentra- 

 tion, indicates that they wander for short distances and establish themselves 

 rather promptly in available suitable material in the immediate vicinity. 



Thus in the dead and hollow weeds, both standing and on the ground, about 

 a series of burials in 1921, 155 larvae were recovered, which had emerged from 

 buried material and were found almost entirely within six feet of the source 

 of supply. In another experiment in which 1,000 larvae were buried in stalks 

 in the centre of a weed patch in 1922, all the larvae recovered were within ten 

 feet of the edge of the burial. Where the material in the surroundings made 

 it possible, the larva? established a sharp density of population gradient. This 

 was well illustrated by a study on a two-foot strip from the margin of this burial 

 at a point where there happened to be a continuous supply of refuse suitable 

 for accommodating borers. Here a count in areas two feet wide and one foot 

 deep, extending westward in a straight line from the edge of the burial for ten 

 feet, gave a count per area of 11, 4, 2, 1, 0, 0, 0, 0, 0, 0, caterpillars. 



There is no decided preference evidenced for movement in any given direc- 

 tion, at least as shown by the recoveries in the traps. There was a somewhat 

 greater number taken on the south side when the larvae within the cage only 

 were considered. However, the total number moving north or south, as indicated 

 by the total count both inside and out, is remarkably evenly divided. 



The following table indicates the distribution of the larvae recovered on 

 the several sides of the traps throughout the season: 



Table III.— Summary of the Direction of Travel of the Larvae Recovered Above a Series of 



Ploughings in 1922. 





Inside of 

 Trap 



Outside of 

 Trap 



Total Going in 

 Given Direction 



Side of Trap 



No. 



% 



No. 



% 



No. 



% 



North 



33 



56 

 27 

 34 



22.2 

 37.3 

 18.0 

 22.6 



49 

 79 

 17* 



37* 



38.2 

 61.7 



112 

 105 

 64* 



51* 



51.6 



South 



48.3 



East 



.... 



West 



• • • • 







*East and West numbers from outside of the trap cannot b° used in account of the nar- 

 rowness of the strips ploughed. * 



With these general behavior studies in mind it is most surprising that it 

 has not been possible to find any indication of migration from ploughed surfaces 

 to adjacent refuse and stubble-littered, unploughed parts of the same field. 



The expected evidence of this migration would be increased larval count 

 in the refuse surrounding the ploughed area, a gradient in density of larval 

 population radiating from the centre of migration and an increment in the number 

 of larvae found spun up in the leaves associated with refuse about this area. 

 These likewise, in the later season, would be expected to be present in somewhat 

 of a gradient. To date none of these relations of the missing larvae present 

 in numbers up to the rate of 30,000 per acre have been established in the areas 

 adjacent to ploughings from which the larvae have disappeared. 



A small proportion of the larvae do find their way into the material left 

 upon the surface of the ploughed ground. These in a given experiment raised 

 the count of this material from an expectation of 0.8 larvae per foot to 5.92 



