1901-] Life-history of Cule:s. patigans. 65 



6. Some Observations on the Life-history of Culex fatigans, the 

 Common Grey Mosquito of Lower Bengal. — By Nellt Evans. 



This investigation was canned out during February and March, 

 in the Indian Museum, Calcutta. 



Culex fatigans will live for about a month if fed on fruit only, but 

 the female does not lay eggs unless she has a meal of blood. A few in- 

 dividuals were kept without food of any kind and some of these 

 lived as long as ten days. Culex fatigans feeds readily on the common 

 house-sparrow, but it was found that the insect would not bite Java- 

 sparrows or larks or rails or white rats, all of which were tried. The 

 common liouse-sparrow was therefore used to supply the necessary meal 

 of blood. 



The female mosquito lays its eggs from four to six days after feed- 

 ing, and the time seems to depend on the amount of blood taken. It 

 was noticed that if the insect gorged itself the eggs were laid on the 

 fifth day or sooner, whereas if less blood was taken, the time between 

 feeding and laying the egg-boat was longer, sometimes as long as ten or 

 fourteen days ; and if very little was taken a second meal of blood was 

 required before the eggs were laid. The female mosquito feeds again on 

 the sparrow the night after laying her eggs, and will lay a second batch 

 of eggs at the end of five days, so that if she is always able to obtain 

 a meal of blood, she will lay a batch of eggs about every five or six 

 days or roughly once a week. 



Of fourteen female mosquitos kept to ascertain the duration of life, 

 and number of repasts of blood, and number of egg-boats laid, two 

 lived for twenty-eight and twenty-nine days respectively and each fed 

 five times on the sparrow and laid five egg-boats ; one died after twenty 

 days, after feeding three times and laying three egg-boats, and one 

 died after eighteen days having fed three times and laid two egg-boats. 

 All the others were either lost or were killed accidentally, some after 

 having laid two or three batches of eggs and having lived thirty and 

 thirty-three days. In those that lived as long as thirty and thirty-three 

 days the time between feeding and laying the eggs was more than five 

 days and in one case was as long as fourteen days. In all these experi- 

 ments a male was kept with the female during feeding as well as 

 before and after. 



Another experiment was tried to see if the female will lay eggs 

 if fed apart from the male. Ross states in his West African Report 

 that the female will not lay eggs unless fed in the presence of the male, 

 that is, that fertilisation takes place after feeding. If the meal of 

 blood is required for the nutrition of the eggs it would seem more 

 reasonable to suppose that the insect's instinct would be to seek the 



