532 ■ PROF. H. MAXWELL LEFROY ON 



We have here to-night representatives of the Press, the 

 educators of the man in the street, and the exponents of his 

 collective opinion, I hope Fellows of the Society will foi-give me 

 if I take the opportunity to urge the Press to emphasise to the 

 Great British Public this fact, that we are actually at a loss to 

 Jcnoio how to meet the fly 2irohlein here and at the front because the 

 necessary scientific investigation has not been done. As a nation we 

 neglect and underrate the value of applied science ; it is not the 

 function of the Zoological Society to deal with the application of 

 Science to national health, and it is the wide sympathies of its. 

 Council and officers that enables me to make use of its resources 

 to deal with this problem : but there is no organised body, no 

 department of Government that stimulates and develops the 

 study of Applied Biology. If there had been, we could answer 

 the questions that come in to us daily from municipal health 

 authorities, Army Sanitaiy officials, and the public, as to means 

 of dealing with flies and other vermin. 



I am not talking in a general way, but I have definite specific 

 problems that are in need of solution at once. 



1. Baits for Flies. — The recommended baits for fly-traps are 

 formalin, beer, vinegar, milk, alcohol, and a few others : these are 

 things arrived at by chance. It seems likely that we might find 

 a really good bait, something that would draw in every fl}^ for a 

 quarter of a mile round, if we worked systematically on the line 

 of testing substances likely to be found in the breeding-materials 

 that flies seek. What brings the fly to the manure heap ? Smell 

 possibly ; if so, can we find a substance of not too intolerable a 

 smell that could be used to bait a trap in a corner of the garden 

 and that would really bring in all the flies. I think we can, but 

 it will require investigation, and it is a bad time to start inves- 

 tigating when the problem is imminent : we have actually begun 

 with the assistance of the Organic Chemistry Department of the 

 Imperial College, and we hope to get something out, but it is 

 work that should have been all done long ago. 



2. Beside baits based on the fly's breeding-place, can we get a 

 bait based on his food ? Why do flies sometimes take formic 

 aldehyde ? Is this the best or the only one, or are there other 

 definite substances of far greater attractiveness to flies which 

 they associate with their food ? It is worth trying, and obviously 

 if we can get a really potent attractor it will help immensely. 



3. Baits based on Sex. — How does the male find the female ? 

 By scent, by sight, by what ? 



I remember in India a planter sent me some fruit-flies with 

 the remark that when he put a particular mosquito essence on 

 his handkerchief these flies followed him continually ; the essence 

 contained citronella oil, and a drop of this oil will bring the males 

 of these flies from all around : investigation showed that the 

 female produces this oil, and it is by its scent that the males find 

 them : we have now a method of dealing with this fly. 



I quote this quite true story as an example ; and it might be 



