2 BULLETIN 408, U. S. DEPARTMENT OP AGEICULTUKE. 



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Of all the substances whicli were foiind to be effective, borax was 

 the cheapest, most generally available, and the most easily transported 

 and handled, but it was open to the objection that excessive amounts 

 added to manure (the probable result of carelessness in apphcation) 

 woidd result in injury to plants grown in soil to which this manure 

 would be appHed (3). It was accordingly considered advisable in 

 these experiments to restrict the use of borax to garbage heaps, out- 

 houses, offal of various kinds, in fact, to any possible breeding mate- 

 rial not intended for use as a fertilizer, and to recommend powdered 

 hellebore for the treatment of all material Hkely to be used for f ertihz- 

 ing purposes. 



Powdered hellebore, when used at the rate of one-half pound per 8 

 bushels of manure, showed a larvicidal action about equal to that of 

 borax when the latter was apphed at the rate of two-thirds of a pound 

 per 8 bushels, and it was evident that no injurious action either on 

 manure or on the growth of plants followed the application; in fact, 

 the hellebore was found to have disappeared from manure after a 

 period of 30 days. The price of powdered hellebore, with that of 

 drugs in general, has increased considerably during the past 2 years. 



The fact that a plant material was found possessing such high 

 larvicidal powers led to an investigation during the past season of 

 various plant materials which were known to contain alkaloids or 

 glucosids, or were thought to possess some value as larvicides. 

 Included in the list to be studied were a number of common weeds, 

 parts of trees, shrubs, etc., which at the present time have no economic 

 value. There seemed to be a possibility that this line of experi- 

 ments might point to some widely distributed and abundant plant 

 containing a substance specifically poisonous to coprophagous larvae. 



The season's work also included tests with fertilizer mixtures, such 

 as calcium cyanamid and acid phosphate, calcium cyanamid and 

 kainit, etc., with the idea that some combination might be found 

 which would possess a high larvicidal power and also increase the 

 fertnizing value of the manure. 



METHODS. 



The methods employed were the same in most details as those 

 described in Department Bulletins 118 (1) and 245 (2). The same 

 cages that had been employed during the season of 1914 were found 

 to be satisfactory. As in the previous tests, 8 bushels of fresh larvae- 

 infested manure were added to each cage and treated in three layers. 

 When any substance was used dry it was also applied in three layers, 

 and each layer of the treated manure was sprinkled with water. The 

 methods for the open-pile experiments were sHghtly modified, so that 

 instead of collecting and counting the puparia after a period of 6 to 8 



