INSECTICIDES 351 



centration of 0.03 per cent gave a kill of 60.4, 62.0, 65.3, and 63.6 per cent 

 to Aphis rumicis, as compared to 70 per cent for the pyrethrins at the same 

 concentration. Most of these compounds showed no signs of decomposi- 

 tion or loss of toxicity for six months. The instability of the pyrethrins is 

 believed to be due to the ketonic alcohol, pyrethrolone. None of the esters 

 produced the typical pyrethrin symptoms when applied to various parts 

 of the cockroach {Periplaneta americana L.). 



Organic thiocyanates. In view of the fact that a number of compounds 

 contaming the SCN group had been reported ^^' ^^ to be toxic to insects, it 

 was decided to prepare and test a number of thiocyanates representing 

 various types. A score or more of organic thiocyanogen compounds includ- 

 ing both aliphatics and aromatics were prepared and tested on Aphis 

 rumicis.-^' ^^^ ^^ Several of these compounds exhibited marked toxicity at 

 a concentration of 0.1 per cent, but also caused injury to nasturtium 

 foliage. When injury and toxicity are considered, 7-thiocyanopropyl 

 phenyl ether proved to be one of the most promising compounds by giving 

 excellent control of Aphis rumicis, mealy bugs, and red spider. The action 

 of this compound on insects was found to be that of a paralytic agent, 

 producing nerve lesions in the meal worm similar to those described for 

 pyrethrum. 



Trimethylene dithiocyanate was found to be equal to or better than 

 7-thiocyanopropyl phenyl ether. Trimethylene dithiocyanate controlled 

 Aphis rumicis, the melon aphid {Aphis gossypii Glover), the citrus mealy 

 bug {Pseudococcus citri Risso), the long-tailed mealy bug (Pseudococcus 

 adonidum L.), the lesser European bark beetle {Scolytus multistriatus 

 Marsh), the potato flea beetle (Epitrix cucumeris Harris), and red spider. 

 Of 75 species and varieties of plants tested in regard to their tolerance to 

 trimethylene dithiocyanate (0.1 per cent), 64 were tolerant as compared 

 with 59 for 7-thiocyanopropyl phenyl ether used at the same concentration. 



When compared at equal concentrations of SCN, lauryl thiocyanate was 

 found to be more toxic than trimethylene thiocyanate to Aphis rumicis, 

 but less toxic than rotenone. 



The toxicity of mixtures of equal parts of rotenone and lauryl thiocyanate 

 was the same as that of a spray containing rotenone alone at a concentration 

 equal to the total concentration of the mixture, and greater than that of a 

 spray containing thiocyanate alone at this concentration.- 



Both trimethylene thiocyanate and phenacyl thiocyanate were ineffec- 

 tive as insect stomach poisons. Guinea pigs fed cabbage leaves sprayed 

 with the first-named compound showed no acute symptoms.^- 



Piperine. It was found by Harvill and others '° that the addition of 

 piperine, the alkaloid found in the dry fruit of black pepper, to a pyreth- 

 rum solution gives a product that is extremely efficient as a housefly spray. 

 Piperine was found to be more toxic than pyrethrum to houseflies, but its 

 paralyzing action was too slow to produce the knockdown required of fly 

 sprays. At concentrations of 0.10 per cent, piperine killed 75 per cent, and 



