Larvicidal potential of Pseudomonas mosselii isolated from Aedes (Diptera: Culicidae) egg surfaces against dengue vector mosquitoes and its impact on non-target organisms.

Abstract

The critical impact of mosquito-borne diseases on public health, along with the failure of current control strategies, highlights the need for novel mosquito control approaches mainly in tropical countries. This study explored the larvicidal properties of bacterial isolates from the egg surfaces of Aedes aegypti L. and Aedes albopictus Skuse (Diptera: Culicidae), the primary and secondary dengue vector mosquitoes in Sri Lanka. Among 30 bacterial isolates, a local strain of Pseudomonas mosselii Quesnel isolated from the egg surfaces of the dengue vectors demonstrated strong larvicidal activity against Ae. aegypti. Larvicidal assays using the bacterial supernatant (OD 1.7) and freeze-dried products were performed across concentrations ranging from 80 to 2.1 mg/mL. The LC₅₀ values for the supernatant were 55, 54 and 52 mg/mL at 24, 48 and 72 h, respectively, with corresponding LC₉₀ values of 91, 89 and 86 mg/mL. Freeze-dried supernatant showed LC₅₀ values of 2.73, 2.64 and 2.63 mg/mL, while freeze-dried bacterial culture showed higher toxicity with LC₅₀ values of 2.57, 2.51 and 2.44 mg/mL. Strong larvicidal activity was observed against Culex quinquefasciatus Say (Diptera: Culicidae), a primary vector of filariasis. The freeze-dried products retained their efficacy for up to 2 months. Ovicidal and adulticidal assays indicated no significant effects on mosquito eggs or adults. However, the active components of bacterial metabolites significantly impacted the development of Aedes larvae. Toxicity effects were observed in non-target organisms, including zooplankton and tadpoles. These findings suggest the local Ps. mosselii strain as a potential bio-larvicide against dengue vectors while underscoring the need for further environmental assessment.