FORMALDEHYDE AS A POISON FOR HOUSE-FLIES. 63 



Table XV. 

 Comparing the Effects of Formaldehyde and Sodiwn Fluoride as Fly Poisons. 





No. of 



tests. 



Aver, 

 flies. 



Aver, percentages dead after : 



Solution. 



1 hour 



4 hours 



24 hours 



1% sodiumT fluoride, 3% 



sugar 

 5% formaldehyde, 50% 



lime water, 3% sugar 



4 

 4 



Ill 

 74 



57 



66 



76 

 74 



94 

 9G 



Summary. 

 The effective action of formaldehyde as a fly poison depends on the freedom of 

 the^exposed fluid from formic acid, and,, to a less extent, from methylamine. That 

 used^for fly poisoning should therefore be colourless and free from a fishy odour, 

 and a weak alkaH, in slight excess, should be added in dilution to neutraUse any 

 acid present and that which will be formed during exposure. The formula recom- 

 mended is : — 



40% Formaldehyde 5-6% 



Clear lime water . . . . . . . . . . . . 50% 



Sugar 2-5% 



Water . . . . , . . . . . . . add to make 100 



This should be exposed in a trap which will protect it from the air and will prevent 



flies from falling in. Formaldehyde, like any other stomach poison for flies, will 



be most elective under dry conditions. 



Rejere7ices. 



1. 0. C. Lodge, Proc. Zool. Soc. Lond,, Sept. 1916. 



2. Thorpe, Dictionary of Chemistry, on formaldehyde. 



3. Mally, C. W. " On the use of poisoned bait for controlling the house-fly : " 



S. African Journal of Science, June 1915. 



4. Jackson and Lefroy, " Some Fly Poisons for Outdoor and Hospital Use ; " 



Bull. Ent. Res. vii, p. 327. 



