Chemical screening, insecticidal and reprotoxic activities of Tecoma stans ethanolic leaf extract against the vector mosquito Culex pipiens

Abstract

To select potential plant-based insecticides, Tecoma stans (Bignoniaceae) leaf extract was screened for its larvicidal and delayed effects against a medically important mosquito species Culex pipiens L. (Diptera: Culicidae). First, gas chromatography–mass spectrometry (GC–MS) was conducted on T. stans extract, collected in ethanol for its chemical characterization and detection of active constituents. Second, insecticidal bioassays were made with several concentrations on earlier fourth instar larvae (L4) of Cx. pipiens for 24 h as recommended by WHO, in order to determine the lethality parameters of the tested extract. For that, two concentrations (LC₃₀ and LC₅₀) were applied on L4 for 24 h, and emerged adults were observed for their reproductive performance success like fecundity, percentage of hatching (fertility), body and gonads' volume. The biochemical composition of whole bodies of adults was investigated. Also, the specific activities of acetylcholinesterase (AChE) and glutathion S-transferase (GST), biomarkers of neurotoxicity and detoxification, respectively, were also determined in L4 at different time intervals. Qualitative and quantitative phytochemical analysis (GC–MS) of the extract unveiled nine phytoconstituents with 2-[4-cyclohexylbutanoylamino]-3-chloro-1,4-naphthoquinone (36.24%) and 1,2-Benzenedicarboxylic acid, mono(2-ethylhexyl) ester (22.65%) as major components. The early L4 of Cx. pipiens were exposed to LC₃₀ and LC₅₀, and after 24 h, surviving individuals have been further reared until adult emergence. All over, T. stans leaves ethanolic extract impairs adults reproductive traits; it adversely affected gonad's size, fecundity and fertility, which negatively affected the survival of their offspring. Lipids contents were found to increase in both male and female adults. T. stans ethanolic extract increased GST activity and slightly inhibited AChE activity in L4. In conclusion, the ethanolic extract of T. stans could be a potential candidate used as a sustainable botanical insecticide for controlling mosquito.