FUMIGATION AGAINST GRAIN WEEVILS 13 



compounds were more toxic than the corresponding chlorine com- 

 pounds. From tests on potato-beetle eggs with bromoform, tri- 

 methylene bromide, o-bromotoluene, and bromoxylene, Moore and 

 Graham (17) concluded that the toxicity of organic compounds to 

 insect eggs increased with decreasing volatility. Moore (15) also 

 tested the action of bromoform, brometone (tribromo tertiary 

 butyl alcohol) , and ethylene bromide on flies. 



Bertrand and Rosenblatt (2) found benzyl bromide to be more 

 toxic than carbon disulphide, but less toxic than monochloroacetone 

 to the larvae of (Bombyx) Malacosoma neustria L. 



Holt (9) found that it took nine minutes for the vapor of bromo- 

 form (0.8 gram per liter) to kill cockroaches (Perivlaneta orientalis 

 L.), as compared with eight minutes for carbon disulphide at the 

 same concentration. 



Organic bromides have the disadvantage of being costly. While 

 the bromides are in general more effective than the corresponding 

 chlorides, they can not be expected to give an economical fumigant, 

 because liquid bromine is usually quoted at a price four to five times 

 that of chlorine; furthermore, 35.5 units by weight of chlorine are the 

 chemical equivalent of about 80 units by weight of bromine. 



Ethylene bromide and ethyl bromide (Tables 3, 4, 5, 6, 7, 8) are 

 the only bromides which seem worth a further trial. 



CHLORIDES 



Trichloroethane, s-tetrachloroethane, propylene dichloride, and a 

 mixture of o- and p-dichlorobenzene gave 100 per cent mortality in 

 concentrations of 2 per cent or less. Other chlorides showed the 

 following order of toxicity: Monochlorobenzene, p-dichlorobenzene, 

 tetrachloroethylene, methylene . chloride, ethylene chloride, carbon 

 tetrachloride, chloroform, acetylene dichloride, trichloroethylene, 

 ethylidene chloride, and isopropyl chloride. 



Tattersfield and Roberts (24) experimented with wireworms. 

 Dichloroethylene, trichloroethylene, carbon tetrachloride, chloro- 

 form, and tetrachloroethane, in the aliphatic series, and mono- 

 chlorobenzene and o-chlorotoluene, in the aromatic series, had a low 

 toxicity; 1, 2, 4-trichlorobenzene, monochloroxylene, p-dichloroben- 

 zene, and benzotrichloride had a marginal toxicity; o-dichloroben- 

 zene and benzal chloride had a moderate toxicity; and benzyl 

 chloride had a high toxicity. 



Parker and Long (19), using several chlorides against the larvae 

 of Trogoderma Ichapra Arrow, at a concentration of 10 ounces per 1,000 

 cubic feet and an exposure of 1,000 minutes, obtained a mortality 

 of 11 per cent with carbon tetrachloride, 27.7 per cent with tri- 

 chloroethylene, 73.3 per cent with tetrachloroethane, and 77.7 per- 

 cent with pentachloroethane. 



Holt (9), Trillat and Legendre (26), Bertrand and Rosenblatt 

 (2), Lefroy (11), McClintock, Hamilton, and Lowe (13), Titschack 

 (25), and many other investigators report that chloroform has a low 

 toxicity against various insects. 



Altson (1), using the vacuum method commonly employed with 

 hydrocyanic acid gas, found tetrachloroethane useless for the fumi- 

 gation of beetles in wood. He recommends both o- and p-dichloro- 

 benzene as a deterrent to timber beetles. 



Lloyd (12) reports that tetrachloroethane gives good results 

 against the white fly in greenhouse fumigation, but is without 



