200 



Grassi (B). Osservazioni suUa Biologia degli Anofeli. Gli Amori 

 degli Anofeli. [Observations on the Biology of Anophelines. The 

 Mating of Anophehnes.] — Ann. d'Igiene, Rome, xxxi, no. 8, 

 August 1921, pp. 453-456. 



In 1921 the author was able to test his theory that Anophehnes 

 mate in the open air. The observations were made in a locality on 

 the Bay of Naples where malaria does not occur. Wesenberg-Lund 

 in his work on Danish Culicids [R. A.E., B, ix, 82] recorded the males 

 of ^. maciilipennis (daviger) in small swarms in June at sunset, approxi- 

 mately 50 yards from a stable where about one hundred gorged females 

 were present ; a few females that did not come from the stable and 

 had apparently not had a feed of blood were seen entering the swarms. 

 The author and other observers noticed on 1 1 th July that the swarms 

 of males, which usually occur near pigsties, began to form at 6.50 

 p.m., the sky being overcast, the temperature relatively low, with no 

 perceptible wind and with intermittent rain. On i2th July the 

 swarms formed at 7.5 p.m., the weather being fine with a moderate 

 wind. The swarms occurred over reed-thatched pigsties, manure 

 heaps and straw heaps, at heights varying from about 20 inches to 

 6h feet. They gradually increased in size. 



Females, presumably coming from the pigsties or from adjacent 

 houses, separately approached the swarms, and though the exact 

 point where mating began was not noticed, pairs were seen either 

 close to the swarms or in them. Immediately after uniting the pairs 

 fly away, usually with the wind. Of three captured pairs one of the 

 females contained blood, apparently ingested some hours before. 

 Relatively few mating individuals were, however, seen during the 

 50-70 minute period of swarming. With the advance of darkness 

 the swarms decrease. On 11th July they disappeared under heavy 

 rain at 7.30 p.m., and on the 12th July at 8.5 p.m., the weather being 

 fine. During these observations, the only mosquitos that attempted 

 to bite the ol3servers were species of Culex. There is no explanation 

 of the fact that so few Anophelines mated. In one instance a swarm 

 captured en masse yielded several hundred males and only two females, 

 while on other occasions no females were taken. The females were 

 never seen to swarm. 



There is little doubt that swarming aims at attracting the females, 

 but it is remarkable that so many males return unmated to their 

 shelters. That some, at least, do return has been proved by tests 

 with marked individuals. It is probable that the most important 

 time of pairing has not been discovered ; possibly it occurs at night. 

 On 20th July a very small swarm was observed at daybreak. This 

 agrees with a previous observation that a few Anophelines come into 

 the open before daybreak [R.A.E., B, ix, 168]. 



It is not possible to say how often mating takes place. In one 

 experiment five mature females died without ovipositing, while twenty- 

 five deposited eggs, three dying immediately after doing so. Of the 

 remainder, twenty-one had been fertilised and one had not been. Of 

 the twenty-five batches of eggs two did not develop. In anj^ case it 

 is clear that one mating suffices for more than one oviposition. 



As a measure against malaria it is not certain whether the capture 

 of swarms is useful. On the one hand it would check the increase of 

 Anophelines, but on the other it would increase the number of females 

 that suck blood without having been fertilised, and it is probable 



