Mosquitocidal activity of Ophiocoma scolopendrina extracts against Culex pipiens and their antimicrobial potential

The current study aimed to study the potential mosquitocidal activities of the crude extract of the brittle star, Ophiocoma scolopendrina against the mosquito vector, Culex pipiens. Regarding the antimicrobial potential of O. scolopendrina, dichloromethane exhibited higher activity than the other solvents; whereas, it could inhibit a wide range of the tested strains with a moderate potential when compared to the positive controls. Larval mortalities exhibited a concentration-dependent pattern. Ethyl acetate, dichloromethane, and ethanol extracts recorded the highest larval mortality percentages with LC₅₀ values of (18.345, 20.45 and 50.966 ppm), respectively. Complete larval mortality was recorded when the 3^rd instar larvae were treated with 80 ppm for dichloromethane and ethanol extracts. Tested extracts disrupted the emergence of adults, where adult emergence percentages were highly affected by tested extracts, in particular when the LC₅₀ concentration of dichloromethane and ethyl acetate extract was applied, it was reduced to (54.88 and 58.47 %), respectively versus100%for the control. Slight to moderate effects on the sex ratio of emerged adults were recorded particularly for LC₅₀ treatments. LC₅₀ concentrations of ethyl acetate and dichloromethane induced remarkable repellency percentages with about 79.12 and 70.83, respectively. Meanwhile, LC₉₅ concentration severely induced repellent activity. Absolute repellent action was reached when the LC₉₅ concentrations of dichloromethane, ethanol, and ethyl acetate extracts were applied. The present study paves the way to discover the potential mosquitocidal and antimicrobial activities of O. scolopendrina that disrupted some biological aspects of larvae and adults of the mosquito vector C.  pipiens of public health importance.