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VII. The effect of Oil of Citronella on tioo species of Dacus. 

 By F. M. HowLETT, B.A., F.E.S. 



[Read February 7th, 1912.] 



Plates XXXIX, XL. 



The observations which form the subject of this paper 

 were made in the course of work on fruit-flies at the Pusa 

 Research Institute. 



The common fruit-flies of Pusa are Dacus diversus, Coq., 

 and D. zonatics, Saund. {Rivellia persicae, Big.). Of these 

 the latter is a serious pest of peaches and mangoes, and 

 like other fruit-flies it is a pest whose attacks are particu- 

 larly difficult to combat. 



With the idea of attracting the females of zonatus to 

 lay eggs, by imitating the smell of ripe peaches or 

 mangoes, a large number of essential oils were experi- 

 mented with. In the course of these experiments I heard 

 that a neighbour had been troubled by some kind of fly 

 settling on him at a time when he was using oil of 

 citronella, sprinkled on his handkerchief, as a mosquito 

 deterrent. Since the smell of this oil in no way resembles 

 that of mangoes or peaches, its effect on Dacus had not 

 been tried, but as soon as a handkerchief wetted with the 

 oil was exposed in the neighbourhood of the peach-orchard 

 it became evident that the smell exercised an extraordin- 

 arily powerful attraction. In less than half an hour the 

 handkerchief, lying in a crumpled heap, was almost hidden 

 by a crowd of D. zonatus, and presented a very striking 

 appearance. I jumped at once to the conclusion that the 

 economic problem of how to destroy female fruit-flies had 

 found an easy solution, but on examination it was soon 

 apparent that all the flies on the handkerchief were males ; 

 they almost refused to leave the neighbourhood of the 

 handkerchief, and a considerable number of them followed 

 me home when I removed it. A handkerchief was pinned 

 to a sheet of cork and exposed in the peach-orchard for 

 twenty minutes, the centre of the handkerchief being 

 moistened with citronella. Plate XXXIX shows the male 

 flies assembled. The cork sheet was then removed for 



TRANS. ENT. SOC LOND. 1912. — PART II. (OCT.) 



