A comparative study of the effect of salinity on egg laying preference, egg hatchability, and larval survival of Aedes aegypti and Aedes albopictus (Diptera: Culicidae): a laboratory assessment

Abstract

Mosquitoes are notorious vectors that transmit pathogenic diseases, including dengue hemorrhagic fever. Since the salinity level affects the breeding behaviour of mosquito vectors, a laboratory assessment was conducted to study the variation of egg-laying preference, egg hatchability, and larval survival of two dengue vector mosquitoes, Aedes aegypti and Aedes albopictus, by exposing them to predetermined periods at varying salinity levels. In this assessment, the egg-laying preference, egg hatchability and larval survival of laboratory-raised Ae. aegypti and Ae. albopictus colonies were measured respectively at 5-day intervals for 25 days at 0 ppt, 5 ppt, 10 ppt, 15 ppt, and 20 ppt salinity levels (n = 3 each). The egg-laying preference, egg hatchability, and larval survival data, each against the salinity level, exposure period and the mosquito species, were analysed by 3-way ANOVA, while the differences in the measured parameters between the two species were analysed by a two-sample ttest. Results revealed that the egg-laying preferences of the two mosquito species did not differ significantly from each other (Ae. aegypti 34.73 ± 6.4 and Ae. albopictus; 35.01 ± 5.9) (p > 0.05). Both species laid eggs from the 5th day upon exposure to the test solutions, and the number of eggs gradually increased with the increasing exposure period. Neither species laid eggs at 15 ppt and 20 ppt salinity levels (p < 0.05). The hatchability of Ae. aegypti eggs (12.9 ± 1.2) were significantly higher than that of Ae. albopictus eggs (9.7 ± 0.6) (p < 0.05). The eggs of neither species hatched at 15 ppt and 20 ppt salinity levels (p < 0.05). The larval survival of both species was statistically similar to each other (p > 0.05), but the survival of both species gradually decreased with the increasing exposure period. The larvae of both species did not survive in 15 ppt and 20 ppt salinity levels (p < 0.05). Since the Aedes mosquitoes thrive in areas close to human dwellings, the addition of common table salt into discarded water-filled containers, both indoors and outdoors, to make the water salinity above 10 ppt (<10 g salt in 1 litre of water) could be used as a promising alternative vector control method in integrated vector management programmes.