282 



and creosote, of which the last-named proved to be the best. 

 Thoug'i these reagents are poisonous to the insects, they also do a 

 great deal of damage to plants, if used in excess. The proper time for 

 spraying is before the floral buds open. If delayed too long, spraying 

 will shake the pollen from the flowers, and in no case should there be 

 any spraying when the blossoms have opened. There is another 

 chance of spraying when the setting season starts and the petals 

 begin to drop off and the fruit becomes set. This final spraying, 

 combined with the previous one, will completely exterminate the insect. 

 .Spraying at different times in the day has varying results ; the same 

 mixture was sprayed over the apple trees at different times in the same 

 day, but the best results were obtained from the noon spraying, when 

 it was bright, windy and hot. 



Three different washes were used : resin w^ash, paraffin emulsion 

 and soap-creosote emulsion. The composition of the first was. 

 lesin, 2 lb., washing soda, 2 lb., and water, 20 gallons ; that of the 

 paraffin emulsion, paraffin, 2 gallons, bar soap, ^ lb., and water 1 

 gallon — this being diluted one part to nine of water. The composition 

 of the soap-creosote emulsion, which was found to be the best, was : 

 100 gallons of water, 10 lb. of soft soap, and 1 qt. of creosote oil (crude 

 commercial) ; one hundred gallons of this wash only cost 25. 6d. 



Several experiments were tried with different percentages of the 

 oil, that of the soap solution being constant, from which it seems that 

 creosote oil in the percentage used ('25 per cent.) is not at all harmful 

 to the trees. The percentages and results of these different apphca- 

 tions were deduced by spraying one of the heavily infested trees, 

 and then each of the four observers broke twigs at random ; these were 

 then spread out on papers, and when dry, the dead and living larvae 

 were picked out. The soap solution, on being mixed with the creosote 

 oil becomes a deadly poison ; it enters the tracheae and blocks the 

 stigmata and thus introduces the creosote into the body. There is 

 no chance of recovery for the larvae, as is the case when soap solution 

 is used by itself. The proportion of creosote, however, seems to be 

 fixed — "25 per cent, being the optimum ; below or above it the results 

 are not satisfactory. 



Cooper (W. F.) & Nuttall (W. H.). Insecticides from a Chemical 

 Standpoint. — Ann. Apjj. Biol., London, i, nos. 3 & 4, January 

 1915, pp. 273-279. 



This paper is a plea for the applicatioii of chemical knowledge to 

 the preparation of insecticides, the formulae for which are but too 

 often purely empirical. It is not enough to know that a given mixture 

 is a useful insecticide, careful experiment is required to determine 

 how it acts and which of the ingredients is the essential one. It has 

 long been popularly supposed that the disinfectant and germicidal 

 value t)f coal-tar lay in the phenol compounds it contains, but it is now 

 known that some of the non-phenolic constituents have an even greater 

 germicidal value. Something cheap and easily obtained is necessary, 

 but the authors urge that there is still a wide range of substances to 

 be studied which comply with these conditions and that what are 

 now laboratory products may possibly prove to be very efficient in- 

 secticides and capable of manufacture at a cheap rate on a large scale 



