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MOSQUITO LIFE IN SURREY DURING 1921. 



By Lt.-Col. S. P. James, I. M.S. (retd.), 



Ministry of HcaWi. 



Mr. Malcolm E. MacGregor's interesting paper, "The Influence of Drought 

 upon Mosquito Life in Surrey " (Bull. Ent. Res. xii, p. 205), has led me to examine 

 our records of observations made in that county in connection with inquiries into 

 indigenous malaria in England. As regards certain areas of the county duiing the 

 past year, our experience of the scarcity of some kinds of mosquitos is the same 

 as Mr. MacGregor's, but (if it is desired to draw conclusions for the county as a 

 whole) it seems important also to note that there are other areas in which the findings 

 differ from those in the particular locality upon which he reported. Dorking, Epsom 

 and Arbrook Common, which are within a few miles of Wisley, are examples of 

 such areas. In these and some other locahties in the county we have obtained 

 larvae of A. bifurcatus without difficulty throughout the year. At Epsom, large 

 numbers of larvae of this species in the fourth instar were found early in February 

 this year in a well-shaded permanent pool, which we have examined regularly since 



1917, and adults were caught in the open in April. Larvae were numerous 

 throughout the year, and adults, both male and female, were captured in the open 

 as late as 22nd October. At Dorking, larvae of bifurcatus were plentiful in several 

 natural collections of water throughout the year. "One of them — the "Mill Ponds 

 stream " — is only 100 yards from a row of houses ; another — the " Stonebridge 

 stream " — yielded bifurcatus larvae on 19th August at every place examined along 

 a stretch of 400 yards. On the same day many larvae of this species were found, 

 along with larvae of C. pipiens, in the rainwater barrel of a house about 200 yards 

 from the stream. 



Next, as regards A. plmnbeus and Finlaya f^eniculaia, we have collected larvae 

 of both species from tree-holes at Dorking and Box Flill on many occasions since 

 the middle of August. Again, the incidence of Tiicobaldia annulata and Ochlerotatus 

 ncmorosns at Dorking and other localities differed this year from that in 

 Mr. MacGregor's area. Adults of Theobaldia annulata were caught in a bedroom at 

 Dorking during July, and larvae have been plentiful in a large stagnant ditch 

 throughout the year. Also it is worthy of note that my laboratory assistant 

 (P. G. Shute) coUected from Arbrook Common in June a larva of a species {Aedes 

 cinereus) which is not included in Mr. MacGregor's list of the species found at Wisley. 



As regards A. maculipennis, Mr. MacGregor records the important observation 

 that, when nearly all the available breeding-places in his area were dry, there was 

 an increase in the actual numbers of larvae found in the breeding-places which 

 remained. As well as similar findings, our records contain the observation that this 

 year the river Wey, at Guildford, for the first time since we began to examine it in 



1918, harboured many maculipennis larvae. During July and August, my laboratory 

 assistant, using a boat, collected numerous specimens along both banks of the river 

 over a distance of a mile. 



This and other observations in Surrey and Kent lead us to believe that the 

 presence in our area ot permanent breechng-places of various kinds sufficiently explains, 

 the differences between the records for our area and for the area examined by 

 Mr. MacGregor. In India, where long periods of drought recur annually, the relative. 



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