Larvicidal and anti-termite activities of microbial biosurfactant produced by Enterobacter cloacae SJ2 isolated from marine sponge Clathria sp

Abstract

The widespread use of synthetic pesticides has resulted in a number of issues, including a rise in insecticide-resistant organisms, environmental degradation, and a hazard to human health. As a result, new microbial derived insecticides that are safe for human health and the environment are urgently needed. In this study, rhamnolipid biosurfactants produced from Enterobacter cloacae SJ2 was used to evaluate the toxicity towards mosquito larvae (Culex quinquefasciatus) and termites (Odontotermes obesus). Results showed dose dependent mortality rate was observed between the treatments. The 48 h LC₅₀ (median lethal concentration) values of the biosurfactant were determined for termite and mosquito larvae following the non-linear regression curve fit method. Results showed larvicidal activity and anti-termite activity of biosurfactants with 48 h LC₅₀ value (95% confidence interval) of 26.49 mg/L (25.40 to 27.57) and 33.43 mg/L (31.09 to 35.68), respectively. According to a histopathological investigation, the biosurfactant treatment caused substantial tissue damage in cellular organelles of larvae and termites. The findings of this study suggest that the microbial biosurfactant produced by E. cloacae SJ2 is an excellent and potentially effective agent for controlling Cx. quinquefasciatus and O. obesus.

Figure 1

Calculation of LC₅₀ values for larvicidal activity. Non-linear regression curve fit (solid line) and 95% confidence intervals (shaded area) on the relative mortality (%).

Figure 2

Calculation of LC₅₀ values for anti-termite activity. Non-linear regression curve fit (solid line) and 95% confidence intervals (shaded area) on the relative mortality (%).

Figure 3

Effect of sub-lethal (LC₅₀) dose of biosurfactant on Culex quinquefasciatus larval development. Light microscope images at 40 × magnification (a) Normal Cx. quinquefasciatus (b) Abnormal Cx. quinquefasciatus larvae.

Figure 4

Histopathology of normal untreated 4th instar larvae of Cx. quinquefasciatus larva (Control: (a,b)) and treated with the biosurfactant (Treatment: (c,d)). Arrow indicates the treated gut epithelium (epi), nucleus (n) and muscles (mu). Bar = 50 µm.

Figure 5

Histopathology of normal untreated O. obesus (Control: (a,b)) and treated with the biosurfactant (Treatment: (c,d)). Arrow indicates the gut epithelium (epi) and muscles (mu) respectively. Bar = 50 µm.