Observations on Released Stegomyia Aegypti (L.)

With Special Reference to Dispersion

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  • Yellow Fever Laboratory of the International Health Division, Rockefeller Foundation, Bahia, Brazil

Summary and Conclusions

During the course of four experiments, 3,500 Stegomyia aegypti were stained and released in an attempt to determine their house abiding time and dispersion. All four lots were released in the same house, and throughout the experiments good conditions in the way of shelter, food, and water were afforded them.

Lots I and II (unfed on blood previous to their release) attacked one of the occupants of the house freely by daylight as well as at night. During one of the night-feeding experiments a light was kept burning in the room; during the other, the room was in complete darkness.

Aequeous solutions of methylene blue (1 per cent) and eosin (2 per cent) proved to be very successful for staining the mosquitoes, while the gentian violet stain (1 per cent) apparently caused the death of the mosquitoes. From 90 to 100 per cent of the mosquitoes were successfully stained.

The mosquitoes were collected in chloroform tubes or in nets. In the great majority of cases the released mosquitoes were found in the bedrooms of the houses.

The recoveries show that (1) dispersion to other houses began within twenty-four hours (experiment IV); (2) at the end of one week's time by far the greater majority (over 90 per cent) had disappeared from the house of release (experiment I); (3) after two weeks, less than 1 per cent could be found (experiment III). One specimen was recovered seventeen days after liberation in a house 120 meters from the house of release.

On one occasion (experiment IV), when the search for the stained mosquitoes was initiated the day following release, 54 per cent was recovered the first day, and during the five succeeding days an additional 15 per cent was obtained. Of these, 66.37 per cent was found in the house of release, while the remainder, 3.12 per cent, were found in one of the adjoining houses. The last specimens (two) recovered in this experiment were found in the house of release.

The results indicate either that the life of the mosquito in nature is usually of comparatively short duration, or that dispersion is very thorough and widespread. The geckos in the house of release were observed devouring numbers of the released stegomyia, and the numerous spiders present no doubt exacted a heavy toll.