Transgenerational Effects of Cadmium and Copper Exposure on Development, Reproduction, and Midgut Integrity in Culex pipiens (Diptera: Culicidae): Implications for Vector Ecology Under Metal Pollution

Abstract

Heavy metal contamination in freshwater ecosystems poses persistent threats to aquatic organisms and public health. This study evaluates the transgenerational toxicity of cadmium chloride and copper sulfate on Culex pipiens, focusing on development, reproduction, and midgut histopathology over two successive generations. Larval bioassays showed cadmium chloride to be more toxic than copper sulfate, with early instars exhibiting higher sensitivity (LC₅₀ = 8.66 μg/L for Cd; 175.63 μg/L for Cu). Both metals significantly delayed larval and pupal development, reduced fecundity, and decreased egg hatchability in a dose-dependent manner. Histopathological examination revealed midgut epithelial degeneration, vacuolation, and brush border loss, with copper sulfate inducing more severe cytotoxicity. These findings confirm that sublethal, chronic metal exposure can impair physiological and reproductive traits across generations. Moreover, this study highlights the utility of mosquitoes as sensitive bioindicators of aquatic pollution, and underscores the long-term ecological implications of heavy metal contamination on vector dynamics and disease transmission.

Keywords: Culex pipiens; aquatic pollution; bioindicator; cadmium; copper; fecundity; histopathology; transgenerational toxicity.

Figure 1

Larval and pupal development time in two successive generations of Culex pipiens following long-term exposure to varying concentrations of cadmium chloride. Significant differences (p < 0.05, three-way ANOVA with Bonferroni test) in the developmental period are indicated by different red letters for the first generation and different black letters for the second generation.

Figure 2

Larval and pupal development time in two successive generations of Culex pipiens following long-term exposure to varying concentrations of copper sulphate. Significant differences (p < 0.05, three-way ANOVA with Bonferroni test) in the developmental period are indicated by different red letters for the first generation and different black letters for the second generation.

Figure 3

Fecundity and egg hatchability of Culex pipiens following exposure to varying concentrations of cadmium chloride across two successive generations. Boxplots labeled with different red letters denote statistically significant differences in fecundity and hatchability percentages among cadmium treatments within the first generation (two-way ANOVA followed by Bonferroni post hoc test, p < 0.05). Boxes marked with different black letters indicate significant differences within the second generation under the same statistical criteria.

Figure 4

Fecundity and egg hatchability of Culex pipiens following exposure to varying concentrations of copper sulphate across two successive generations. Boxplots labeled with different red letters denote statistically significant differences in fecundity and hatchability percentages among copper treatments within the first generation (two-way ANOVA followed by Bonferroni post hoc test, p < 0.05). Boxes marked with different black letters indicate significant differences within the second generation under the same statistical criteria.

Figure 5

Cross-sections in the gut of the 3rd instar larvae of the mosquito Culex pipiens. (A) Control (X = 100), (B) larvae exposed to the LC₅₀ concentration of CdCl₂ in the 1st filial generation (X = 200), and (C) larvae exposed to the LC₅₀ concentration of CdCl₂ in the 2nd filial generation (X = 200). (D) Larvae exposed to the LC₅₀ concentration of CuSo₄ in the 1st filial generation (X = 400), and (E) larvae exposed to the LC₅₀ concentration of CuSo₄ in the 2nd filial generation (X = 400). (N) nucleus, (L) lumen, (Gr) granules, (BB) brushing border, (ec) epithelial cells, (Ip) inferior protuberance, (Mv) microvilli, (dec) degenerated epithelial cells, (dn) degenerated nuclei, (V) vacuolation, (Fec) fused epithelial cells.

Figure 6

Bar charts showing the morphometric measurements of in the gut of the 3rd instar larvae of the mosquito Culex pipiens. (A) Control, (B) larvae exposed to the LC₅₀ concentration of CdCl₂ in the 1st filial generation, (C) larvae exposed to the LC₅₀ concentration of CdCl₂ in the 2nd filial generation, (D) larvae exposed to the LC₅₀ concentration of CuSo₄ in the 1st filial generation, and (E) larvae exposed to the LC₅₀ concentration of CuSo₄ in the 2nd filial generation. Values are represented as mean ± SEM, and n = 10 larvae.