2 CIRCULAR 349, U. S. DEPARTMENT OF AGRICULTURE 



It can readily be seen that various factors, such as moisture content, 

 texture, and packing of the soil, have an important bearing on the 

 proper depth fruit should be buried. Undoubtedly the different 

 species of fruit flies vary considerably in their ability to overcome the 

 same conditions imposed to prevent their emergence from the soil. 



EXPERIMENT IN 1931 



This experiment was conducted in Cuernavaca, Morelos, Mexico, 

 in a location exposed to the sun. The experiment was divided into 

 two series; one in which the surface of the soil was packed with a 

 tamper, the other in which the soil was left unpacked. No trees bear- 

 ing infested fruit were nearer than 200 feet to the plot. The work 

 was done in the dry season when the soil was extremely dry and hard. 

 Natives formerly made adobe bricks in part of the field where the plot 

 was located. The soil was broken up as much as possible at the time 

 the pits were dug. The fineness of the soil is shown in table 1. 



Table 1. — Size of soil particles used in experiment in 1931 in burial of fruit infested 

 with larvae of the Mexican fruit fly 



Size of mesh of sieve 



Weight 

 of soil 



Propor- 

 tion of 

 total 

 weight 



Size of mesh of sieve 



Weight 

 of soil 



Propor- 

 tion of 

 total 

 weight 



Mm 



1 

 3 

 5 



Inches 



0. 0394 



.1181 



.1968 



Grams 

 3,279 

 1,534 

 1,522 



Percent 

 29.96 

 14.02 

 13.91 



Mm 



12 

 35 



Total. .. -. 



Inches 



0. 4724 



1. 3779 



Grams 

 2,457 

 2,151 



Percent 

 22.45 

 19.66 





10. 943 



100. 00 





The pits were dug and the piles of soil exposed to the sun several 

 days before the fruit was buried. Each pit was approximately 2 feet 

 square. The pits were so spaced that a wall of at least 12 inches of 

 hard, dry adobe separated them. There was no possibility of larvae 

 or adults from one pit becoming mixed with those of another. Seventy 

 infested mangoes were placed in the bottom of each pit. The fruit 

 was closely packed to simulate the condition that would exist at the 

 top of the fruit buried in a large pit. The fruit was immediately 

 covered after placing it in the pit. The soil was carefully shoveled 

 into the pits, not scraped into them, from the sides. This prevented 

 the larger pieces from accumulating in certain parts of the pits, as they 

 would if the soil were scraped into them. 



Eighteen pits were used in the experiment; 8 in the packed series, 

 8 in the unpacked series, and 2 controls. The depth at which fruit 

 was buried was measured from the top of the fruit in the pits to the 

 surface of the soil. Two additional inches were allowed for the space 

 occupied by the single layer of mangoes in each pit. The pits in the 

 unpacked series were 18, 22, 23, 26, 26.5, 27, 28, and 40 inches deep, 

 respectively. Those in the packed series Were 19, 22, 26, 27, 30, 33, 

 34, and 40 inches deep, respectively. 



The soil of the pits in one series was packed with a light wooden 

 tamper having a packing surface of 17 square inches. It weighed 11.5 

 pounds, most of the weight being at the tamping end. The packing 

 was done by giving a single impact of the tamper to each part of the 

 surface of a pit until the entire top was packed once. The soil of each 

 pit sank approximately 1 inch, even though some of the pits were 



