174 



after a separate feed. The rapidity with which it may reproduce is. 

 remarkable, the life-cycle occupying 10 days, or in warm weather Si- 

 days, while a female may live for 8 weeks, in which time its progeny 

 would total 2,600. A certain amount of moisture and moderate 

 temperature favour longevity, the mites dying from w^ant of food 

 much faster in the summer months than in the winter ; it should 

 therefore be possible to eradicate them from a chicken-house by 

 keeping fowls and other animals away from it for four months during 

 the summer or five months in winter. Normal feeding takes place 

 during the hours of darkness and the mites leave the fowl after 

 engorgement, which takes from 20 to 30 minutes. The direct rays of 

 the sun act as a powerful killing agent and a dark, protected place is 

 necessary for oviposition and moulting, a crack in a board, dry manure 

 or litter, and the perches themselves being favoured situations. Hence 

 it is necessary to clear away all manure and rubbish before trying to- 

 Idll the mites by spraying, while the perches should be of a type that 

 can be easily removed. Among natural enemies a small black ant, 

 Monomorivm minimum, Buckley, has been seen to carry away 

 recently-fed mites, while the fire ant, Solenopsis geminata, F., destroys 

 many individuals, as also do certain spiders. 



The mites may be disseminated by transferring infested fowls to 

 clean localities ; by using boxes and crates in which infested fowls 

 have been kept ; by mechanical carriers, such as the clothing of man, 

 the feathers of sparrows and pigeons, and the skin of domestic animals 

 and some wild animals, such as foxes, skunks and weasels ; and by the 

 migration of mites to buildings in contact with or close proximity 

 to infested premises. 



Moore (W.). Volatility of Organic Compounds as an Index of the 

 Toxicity of their Vapours to Insects. — JL Agric. Research, 

 Washington, B.C., x, no. 7, 13th August 1917, pp. 365-371,7 figs., 

 1 table. 



The question of relationship between boiling point and toxicity, as 

 existing among volatile organic compounds other than the benzene 

 derivatives, has been worked out by the author on lines similar to 

 those employed in his investigation on the latter [see this Revieiv, 

 Ser. B, V, p. 131]. The insect used in the tests was the house-fly, 

 Musca domesiica, L., and the results are shown in a table and several 

 graphs. A great variety of chemicals were dealt with and it was 

 found that, generally speaking, the less volatile the chemical the more 

 toxic it is, even when the compounds are strilvingly difi'erent in their 

 chemical composition. Exceptions, such as carbon bisulphide, ethyl 

 mercaptan and particularly chlorpicrin, are due, not to vapour density, 

 nor primarily to water solubility, but to their chemical composition or 

 some peculiar action of the chemical concerned. Ethyl alcohol proved 

 more toxic to insects than methyl alcohol, being the reverse of that 

 which takes place in higher animals. The probable explanation of the 

 relation between volatility and toxicity seems to be that the vapour 

 present in the air is taken into the tracheae of insects and is condensed 

 upon reaching their finer divisions. Hence, if the compound is very 

 volatile, it will evaporate and readily pass out of the insect, but if 

 slightly volatile, it will remain, penetrate the tissues and produce ■ 



