Abstract
The present study was carried out to evaluate the activity of methanol, ethyl acetate, chlorobenzene, and hexane extract from leaves of Otostegia fruticosaas larvicidal and repellent agents against Culex pipiens. The effect of tested extracts on the female reproductive potential treated as larvae was also investigated. The obtained results showed that hexane extract have potent larvicidal activitywithLC50 and LC90 values equal to (126.27 and 236.84 ppm), respectively followed by chlorobenzene (242.14 and 501.17 ppm), ethyl acetate (578.07 and 856.29 ppm) and methanol (653.00 and 1127.10 ppm). All tested extracts of O. fruticosa induced significant (P<0.01) reduction in fecundity and increased the infertility percentages of C. pipiens females developed from treated larvae as compared with control and these effects were solvent- and concentration-dependent. In addition, the repellency effect of tested extracts was found to be varied among tested extracts. Four hours post-treatment, the dose of 3.33 mg/cm2 recorded repellency percentages of 64.13 and 75.09 by methanol and ethyl acetate extracts, respectively. Meanwhile, chlorobenzene extract induced repellency percentages of 80.15, 75.94, and 65.84 for the doses of 3.33, 1.67 and 0.83 mg/cm2, respectively. Moreover, repellent activity of hexane extract at doses of 3.33, 1.67 and 0.83 mg/cm2 recorded 88.08, 79.01 and 75.50%, respectively.
Highlights
Culex pipiens L. is reported as one of the most widely distributed mosquitoes worldwide (Shehata 2019)
In Egypt, C. pipiens is widely distributed in the urban areas of Cairo governorate (Ammar et al, 2013) and it is the main vector of Rift Valley fever virus (Meagan et al, 1980; Darwish and Hoogastrall, 1981), Wuchereria bancrofti (Khalil et al, 1930; Gad et al, 1996; Fouda et al, 2013; Hassan et al, 2013) and Western Nile virus (Pelah et al, 2002)
Larvicidal Activity: Obtained results revealed that, complete larval mortality 100% was obtained by methanol extract of Otostegia fruticosa at a concentration of 1400 ppm, for ethyl acetate it was achieved by the concentration of 1000 ppm, respectively compared with 0.0% for the control group (Table 1)
Summary
Culex pipiens L. is reported as one of the most widely distributed mosquitoes worldwide (Shehata 2019). Culex pipiens or the house mosquito is widely distributed in the urban and peri-urban areas (Bernard et al, 2001; Cetin et al, 2013). Immature stages (eggs, larvae, and pupae) are usually targeted by synthetic insecticides (Shehata 2019). (Hemingway and Ranson, 2000; Gold et al, 2001) From this point of view, researchers diverted their attention towards the plant kingdom to find alternative agents that possess bioactive chemicals that may act as potential insecticides, antifeedants, oviposition deterrents, repellents as well as growth inhibitors (Murugan et al, 1996; Koul 2005; Hasaballah 2015; Bream et al, 2018)
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