Studies on the Responses of the female Aëdes Mosquito

Abstract

The responses of females of Aëdes aegypti (L.) to beef blood have been investigated. Paired comparisons were made of the numbers of mosquitos attracted to test and control materials.Vapours emanating from the heparinised blood were found to be significantly more attractive than water vapour in an olfactometer. When the blood vapour was passed through an aqueous solution of Ba(OH)₂ this attractiveness disappeared.Exposure of heparinised blood on filter paper proved it to be two to four times as attractive as water or washed corpuscles suspended in saline. Plasma proved to be 4·7 times as attractive as water, indicating that the attraction of blood lies entirely in the plasma.Treatment of blood with BaCl₂ and a vacuum, thus rendering it incapable of evolving CO₂, removed its attractiveness to mosquitos. Treatment with vacuum alone, which may be expected to remove the volatile substances, did not completely remove the attractiveness; nor did the treatment with BaCl₂ alone, which removes the bicarbonates in the blood.The attractiveness of blood was completely removed by desiccation and was not returned by remoistening. No attractive substance was isolated in an ether extract of blood.When CO₂-freed blood was treated with gaseous CO₂ its attractiveness was significantly increased. When the treatment was such as to restore the normal CO₂-producing capacity, the attractiveness was one-half that of whole blood. The attractiveness of whole blood was not increased by adding excess CO₂.It is concluded that the CO₂ in beef blood is a definite element in its attractiveness, though probably not the most important one.