314 



THE AGRICULTURAL NEWS. 



Sepembee 23, 1916 



INSECT NOTES. 



THE DISPERSION OF THE HOUSE-FLY. 



Effective control of the house-H}' is a world-wide 

 problem of the greatest importance, intimately associa- 

 ted with the maintenance of public health. Two papers 

 in the American Journal of Economic Entomology 

 (Vol. 9, No. 8) add considerably to the knowledge 

 required to achieve this end. The first paper deals 

 with the subject of the migi'atory movements of the 

 fly, and the following is a summary of the data and 

 results obtained in an extensive e.xperiment 



In a city, the built-up portion of which was about 

 lA miles square, .3s7,f<77 marked Hies were liberated from 

 four release points. The release points were so located as 

 to give an idea of the possible spread of flies from breeding 

 areas vaiiously situated in relation to the city as a whole, 

 and each representing difterent conditions. 



A total of 1,056 flies were recaptured at seventy-eight 

 stations, which varied from .50 to 3,500 yards from the point 

 of release. This was the greatest di.stance at which recaptures 

 were attempted. 



The results indicated that under conditions which are 

 favourable, flies may spread from any given breeding ground 

 to all parts of a city, even nne of considerable size. Also that 

 they may not only cross a cit3- offering abundant feeding 

 and breeding areas, but may even leave it and cross open 

 country to points considerable distances beyond its limits. 



The full possibilities of dispersion were not determined, 

 due to the relatively small size of the city, but the fact that 

 the flies spread from release points on one border to points on 

 the opposite side, indicates a possible radius of 2,333 yards 

 (li^ miles), and that flies even traversed the entire city and 

 crossed open country to points beyond, justifies the belief in 

 a still greater radius. The actual territory over which flies 

 were recovered in the city was about 2 square miles, but 

 possible dispersion over a territory of from 5 to more than 

 12 square miles was indicated. 



While the results of this investigation arc of general 

 application to Montana cities and towns, it is problematical to 

 attempt to apply them to more thickly populated areas, where 

 sanitary ineasures an' more easily and more generally applied. 

 Control measures mean fewer flies and fewer feeding and 

 breeding areas, but does this mean a larger or a smaller radius 

 of dispersion for what flies there may be? 



SLOI.MAl;V OK DEIIKCTIVE RESULTS. 



Housefly dispersion (the spread of house-flies from 

 their breeding grounds and the factors controlling it) may be 

 considered as a problem concerning short periods of time 

 or as one of seasonal significance. 



The factoM which control dispersion are mainly, if not 

 entirely, external stinuili. As regards their effect on the 



radius of distribution, these stimuli may be termed inciting 

 (e.g., odours from feeding and breeding grounds), or inlahit- 

 iny (e.g., low temperature, rain). Inciting stimuli givt rise 

 to tropic reactions, movements to aad from, and consequently 

 have a direct eSect on distribut: jn. Inhibiting stimuli 

 indirectly affect distribution, because of resulting periods of 

 inactivity on the Dart of the fl}'. 



These stimuli, both inciting and inhibiting, form a com- 

 plex set of external forces, each if which varies in intensity 

 and duration. 



The adult life of the house fly it esse-itiallj- devoted to 

 two purposes, feeding and reproduction. Hence, it is evident 

 that when dispersion is considered as a problem of long 

 periods or of seasonal duration, the stimuli from feeding and 

 breeding areas are those of the inciting -stimuli which act 

 most continuously and for the greatest portion of a fly's life, 

 and are the most important ones to control. Temperature is 

 a constantly present stimulus, but may be inciting or iuhib- 

 iting. 



When dispersion is considered for short intervals, other 

 stimuli than those from feeding and breeding areas may 

 assume greater importance. These stimuli may be inciting 

 or inhibiting, and under normal conditions have but minor 

 significance as seasonal factors. Cities or localities undoubt- 

 edly occur, however, in which unusual physical or meteoro- 

 logical conditions are present with but slightly varying inten- 

 sity during a complete season, and consequently what would 

 ordinarily be a stimulus of minor importance maj- become one 

 of major seasonal importance (e.g., strong wind blowing con- 

 stantly from some direction, long continued rain, etc.). 



By conducting dispersion experiments with a sufliciently 

 large number of flies for a sufliciently long time, and by cov- 

 ering a sufficiently large territorj-, it seems likely that a limit 

 for fly dispersion, under city conditions, could be determined 

 which would be of more or less general application. The 

 length of time would have to be at least equal to that of the 

 average length of house-fly life. 



Desteuctiok of Larvae. 



The second paper concerns the breeding habits of 

 the Hy. It was found that the development of eggs 

 and larvae in manure was inhibited by all strengths 

 of hydrochloric acid; though the pupae develop from 

 both acid and alkali which is prohibitory to the eggs 

 and larvae. Manure stored in bins was found not to be 

 a good place for the breeding of flies, due to the growth 

 of mould. 



It has been found possible to destroy the larvae of 

 the domestic &y by merely turning the inner parts of 

 the pile over the fresh manure which contains larvae. 

 The heat generated by the nuiinire, as well as the gases 

 which are formed during fermentation are very fatal 

 to the larvae when they are exposed to them. This is 

 a residt of much practical importance owing to the 

 simplicity of this method of control. 



DEPARTMENT NEWS. 



The Imperial (.'(unmi.ssioncr of .\griculture returned 

 to Barbados on September 20 by the C.R.M.S. 'Chau- 

 diere', after having paid an ofhcial visit extending over 

 a month to the Leeward Islands. 



