Susceptibility of Culex pipiens from Essien Udim, Nigeria to the Essential Oil of Corymbia torelliana (K. D. Hills & L. A. S. Johnson)

Mosquitoes serve as major vectors of disease-causing organisms such as filarial worms, malaria parasites, and arboviruses in sub-Saharan Africa, including Nigeria. Effective vector surveillance is critical in the control and elimination strategies. This study was conducted to evaluate the efficacy of Corymbia torelliana essential oil against Culex pipiens mosquitoes from Ukana Uwa West and Adiasim Ikot Essiendot both in Essien Udim local Government area of Akwa Ibom State. Larvae collected from both communities were reared to adults. Adult mosquitoes were morphologically identified using standard taxonomic keys and Culex pipiens was used for susceptibility tests. Test oil was obtained from the flower and flower buds of Corymbia torelliana by hydro-distillation and the composition determined via Gas Chromatography-Mass Spectrometry (GC-MS). From 4 ml stock solution, 31.25, 62.50, 125 and 250 and 500 µl/mL concentrations of C. torelliana oil were prepared using two-fold serial-dilution with 10% Tween 80 as diluent. Each concentration and control had 100 adult mosquitoes exposed. Essential oil from C. torelliana revealed 18 volatile compounds. Major constituents included α-Terpineol (34.60%), α-Pinene (10.15%), p-Cymen-8-ol (8.27%), Copaene (6.53%), and Verbenol (5.47%). Susceptibility tests showed that Cu. pipiens from Adiasim Ikot Essiendot was more susceptible to the oil than those from Ukana Uwa West. Complete knockdown was achieved at 125 µl/mL after 30 minutes with Cu. pipiens from Adiasim, while 250 µl/mL was needed with Cu. ppiens from Ukana. Full mortality occurred at 500 µl/mL in both populations. Probit analysis confirmed lower KD₅₀ and LC₅₀ values for the Adiasim population, indicating higher sensitivity. These findings suggest that C. torelliana essential oil has potential as a natural adulticidal agent against Cu. pipiens, one of the causative agents of lymphatic filariasis.