18 BULLETIN 118, U. S. DEPARTMENT OF AGRICULTURE. 



taken to the laboratory and examined daily under a microscope. 

 None of these hatched after a week at room temperature and favor- 

 able moisture conditions. On October 6, in going over a pile, last 

 treated with borax solution on September 28, batches of a thousand 

 eggs or more were found. They had a bluish tinge. A mass of these 

 eggs with surrounding manure was kept in a jar in the laboratory 

 for a week and examined daily. None had hatched at the end of this 

 time. Similar observations were made on other borax-treated piles. 

 No such masses of unhatched eggs were ever found on control piles, 

 nor on piles treated with other chemicals after the first three or four 

 days of exposure. 



Calcined colemanite, being largely insoluble, did not show this 

 effect on the eggs. Borax acts very effectively through its toxic action 

 on the eggs, but its action is not confined to the egg stage, as larva? 

 are also killed. In nearly all cases examinations of open piles showed 

 the presence of dead larvae as well as pupa?. In Table V it will be 

 noted that in some piles large numbers of pupae were found, but 

 these were black, shrunken, wrinkled, and were not normal in shape, 

 having more nearly the form of the larvae than of the pupae. 

 PI. IV.) When kept in the laboratory for a long time 1 per 

 cent or less hatched. The borax had evidently killed them just at 

 the time of transformation from larvae to pupae. This may be ex- 

 plained in several ways. (1) It may be that the larvae, in the 

 younger stages, resisted the action of the borax they had ingested 

 but became very sensitive to it at the time of the breakdown of larval 

 tissues. (2) The action of the borax may be cumulative and so may 

 not evidence its toxic action until toward the end of the larval stage. 

 (3) It may be that the larvae in their earlier stages were found some 

 distance in from the surface where the borax had not penetrated, but 

 that, when ready to pupate, they migrated to the outer lower edges of 

 the manure pile where the concentration of the borax was greatest and 

 were killed by it. The migration of the larvae in the cages and open 

 piles has already been referred to on pages 3 and 5, and is discussed 

 more in detail by Mr. Hutchison (1914). 



The fact that small quantities of borax are not detrimental to the 

 normal fermentation of manure is further shown by some temperature 

 determinations. 



The manure piles were made with no attempt to pack the manure, 

 because it was believed that the higher temperatures prevailing where 

 aerobic fermentation was in progress would be an attraction to the 

 flies. Three series of experiments were used for these tests. The 

 temperatures were taken by inserting a thermometer about a foot 

 deep in the top of the piles. As the piles were small the temperatures 

 at this depth were very nearly the maximum. The three controls 

 attained their highest temperature, 66° and 67° C. (150.8° and 152.6° 



