Impact of Green Alga, Chiorella ellipsoidea , 1 on Development and Survival of Mosquitoes Breeding in Cemetery Vases

Abstract

The alga Chlorella ellipsoidea Gerneck caused 85% reduction in the populations of mosquitoes breeding in cemetery vases. Annual mean larval densities of 9 and 61 larvae per vase were observed in algal and nonalgal vases, respectively. The maximum mean larval density of 17 larvae per vase in algal vases was significantly lower than the corresponding maximum (131 larvae per vase) in the nonalgal vases. The low numbers of mosquito larvae prevailing in the algal vases were likely due to the action of toxins produced by C. ellipsoidea . Lower larval densities, “0” and “1–10” larvae per vase, were found in 57 and 24% of the algal vases, respectively, whereas these densities occurred in 22 and 12%, respectively, of the nonalgal vases. The percentages of nonalgal vases supporting the three higher densities (26–50, 51–100, and > 100 larvae per vase) were significantly higher than those of the algal vases. The number of vases with and without algae supporting first- and second-stage larvae was similar, however, the number of vases supporting third- and fourth-stage larvae and pupae was significantly higher in the nonalgal than in the algal vases. The percentage of algal vases containing dead larvae or pupae was significantly higher (ca. 11 times) than that of the nonalgal vases. Studies on algal growth revealed that an overall average of 23% of the vases contained C. ellipsoidea during the study period. The incidence of this alga peaked during May (33% vases with algae) and was lowest in December (7%). No apparent relationship between algal density and mosquito numbers was observed.