Exposure to copper metal enhances the tolerance of An. gambiae s.s. over multiple generations while reducing both fertility and fecundity in this primary malaria vector .

Abstract

Background: Anopheles s.l. displays the potential to develop tolerance to heavy metals, particularly copper, this may occur at a significant biological cost, which can adversely affect its ecological fitness. This study investigated the larval metal exposure on larval development and reproduction of An. gambiae s.s., a laboratory susceptible strain, kisumu.

Methods: Stage 2 larvae of Anopheles gambiae, Kisumu were exposed to C ₁ = 484 μg L ^-1, C ₂ = 300 μg L ^-1 and 0 μg L ^-1 (control) of copper chloride. Larval mortality, pupation time, pupation rate, gonotrophic cycle length, fecundity and fertility of larvae/adults were assessed over six generations.

Results: Results revealed that larval mortality rate was significantly higher in the C ₁ groups of each group (p = 0.000), but this mortality rate decreased over generations. Pupation time was extended to 13 and 14 days respectively for C ₂ and C ₁ groups (p = 0.000) compared to the control group. Similar results were observed for the gonotrophic cycle, which increased from 4 days at G0 to more than 6 days at generation 5 in adults of C ₁. The pupation rate in generation 4 (C ₁) and generation 5 of the same group (p = 0.000) as well as the emergence rate in generation 4 (C ₂, p = 0.000) and generation 5 (C ₁ and C ₂, p = 0.000) decreased significantly compared to the control group. The average number of eggs laid was lower in the test groups from generation 4 to generation 5 (C ₁ and C ₂, p = 0.00) and egg fertility was also negatively affected by exposure of the larval stage of An. gambiae s.s. to copper.

Conclusion: This study showed that copper not only exhibits larvicidal properties in Anopheles gambiae s.s. larvae, it also revealed the potential of this metal to reduce fecundity and fertility in these malaria vectors.