SIGNIFICANCE OF STEGOMYIA FASCIATA IN WEST AFRICA. 245 



developmental cycle of this insect in any given localitvj and it may be taken 

 as a general rule that cold will retard any one o£ the stages either of the ova, 

 larvae or pupae ; while a rise in temperature will so shorten the cycle as to 

 bring it within the shortest period possible. 



The Egg. — Under normal conditions the incubation period, in the Amazon 

 region, has been found to vary from 3 to 8 days ; the average, however, may 

 be taken as 3-4 days. 



Larval Stage. — The minimum period as given by Francis (Publ. Health & 

 Mar. Hosp. Serv. Rep. xxii, 1907, p. 382), in water kept at an even tem- 

 perature of 80° F., was 7 days. In Newstead's record (Journ. Trop. Med. & 

 Paras. Liverpool, iv^ p. 143), 9 days are given and the temperature that of 

 23° C. ( = 73-4° F.). Mitchell* states that the larval stage extends over a 

 period of from 8-13 days " in fairly warm weather." 



Pupal Stage. — The duration of this stage varies from 1-5 days. Mitchell 

 (/. c.) gives 1-5 days ; Newstead 2-3 days in a temperature of 23° C. 



Adults. — The female lays her eggs in from 6-15 days after taking the first 

 meal of blood, but Mitchell (1. c. p. 148) states that the female may feed two 

 or three times before laying the first batch of eggs. I'he average number 

 of separate batches of eggs laid by a single female may be given as 2-3 ; 

 but as many as nine batches have been laid in some cases. 



The eggs are extruded singly, and the number laid on each occasion varies 

 from 27-97. Goeldi t found that as a rule the females died immediately 

 after the final act of parturition, though in two instances females survived 

 for 12 and 14 days respectively. He also states that fertilized ova may lie 

 latent in the bod}^ of the parent for from 23-102 days, and that the female 

 may lay her eggs at the end of these periods, respectively, after taking a 

 meal of blood. It is evident therefore that ovulation is retarded until 

 suitable food is obtained. 



It is generally held that the females feed almost exclusively upon warm- 

 blooded vertebrates, and it is usually supposed that such food is necessary 

 for the development of fertile eggs. Goeldi succeeded however in inducing 

 females to feed upon honey, a diet upon which they survived for periods 

 varying from 31 days to, in one instance, 102 days, though it is evident that 

 such food has a retarding or neutral effect upon ovulation. 



Males of Stegomyia fasciata also survived on honey for periods varying 

 from 2S to 72 days. 



These important data point to the fact that in a state of nature both sexes 

 may, as occasion serves, feed upon the nectar of flowers, though one has 

 failed to find, in the innumerable publications which have been issued 

 regarding the habits of this insect, any evidence that this actually takes 

 place under natural conditions. 



* ' Mosquito Life,' p. 148, 1907. 

 t * Os Mosquitos no Para.' 



