Annual Research & Review in Biology

Crude extracts of marine sponges, Negombata magnifica and Callyspongia siphonella were tested for their antimicrobial activity besides larvicidal, pupicidal, adulticidal and other biological effects against the filarial vector Culex pipiens. Three sub-lethal concentrations ranging as 8.4, 28.4 and 47.6 ppm for N. magnifica and 44.5, 327.4 and 610.3 ppm for C. siphonella were used.

The two marine sponges used in this study were collected from reefs by SCUBA diving. Spicules were prepared by dissolving the soft tissue of small pieces of sponge in sodium hypochlorite and washed with distilled water and ethanol. The extracts were tested for their antimicrobial activity; in addition, the biological activities of the three sub-lethal concentrations used were evaluated against laboratory reared Cx. pipiens mosquito.

The results obtained showed interesting antifungal activity against fungal strains tested. N. magnifica extract showed quite promising broad-spectrum antibacterial activity due to its capacity to inhibit the growth of almost bacterial strains tested. Based on LC₅₀ values, the toxicity of N. magnifica extract (47.6 ppm) was higher than that of C. siphonella (610.3 ppm). Mean larval and pupal durations of mosquitoes treated with N. magnifica extract were significantly (P<0.05) prolonged at higher sub-lethal concentrations; meanwhile, C. siphonella showed non-significant (P>0.05) prolongation. The N. magnifica extract was found to be more effective against the adult emergence than C. siphonella. There was a pronounced effect of the tested extracts on the number of eggs laid per female and this effect was concentration dependent, the fecundity of mosquitoes treated with N. magnifica extract was significantly (P<0.05) decreased to 86.7±5.8 eggs/♀, compared to 150±8.7 eggs/♀ for the control group, while it was 116.7±5.8 eggs/♀ for C. siphonella extract, vs. the control group. Vitellogenin synthesis and ovarian development of Cx. pipiens females were highly affected by tested extracts. Six protein bands with high molecular weights (175-90 KDa), which believed to be vitellogenin, were detected in the control group, while this number reduced to two bands in ovaries of N. magnifica and C. siphonella-treated females. Also, N. magnifica extract induced concentration dependent repellent activity against tested females mosquitoes than C. siphonella extract. These promising results in relation with antifungal and antibacterial activities open the way for complementary investigation in order to purify and identify active molecules.

The present investigations have helped to focus on some bioactive substances isolated from marine resources; these molecules, which possess antimicrobial and insecticidal activities, could be used as insecticidal agents.