Botanical biocides .12. Mosquitocidal activity of citrus peel oils with respect to their limonene content

الملخص EN

Peels from six species of citrus fruits, namely: Mandarin (Citrus reticulata Blanco), Grapefruit (Citrus paradise Macfad), Native Orange (Citrus sinensis L.), Sour Orange (Citrus aurantium L),. Lemon (Citrus limon L.) and Lime (Citrus aurantiifolia Swing,) were subjected to hydrodistillation for separating their essential oils.

The obtained oils in addition to its Limonene content and the insecticide Malathion were bioassayed against the mosquito, Culex pipiens L.

In larvicidal tests, the LC50 values in descending order of toxicity were: 77.6 ppm for Lime oil; 83.7 ppm for Grapefruit oil; 105.8 ppm for Lemon oil; 116.3 ppm for Native Orange oil; 135.5 ppm for Mandarin oil and 136.4 ppm for Sour Orange oil. Limonene showed LC50 of 126.1 ppm, while that of Malathion was 1,06 ppm.

Mixing citrus peel oils together or with Malathion, (in pairs combinations), at a concentration level equalled to LC25 of each, resulted in potentiation effects against the mosquito larvae. Among the 21 tested mixtures, Malathion + Lemon oil showed the highest degree of potentiation (co-toxicity factor = 100).

Five of the tested oils showed efficacy against the mosquito adults, and the highest potency was entitled to Lemon oil (LC50 = 0.032 mg /cm2), while the lowest potency was given by Native Orange oil (LC50 = 0.140 mg/cm2).

Limonene was less potent than the oils and hadLC50 of 0.165 mg /cm2.

Among the six tested oils, only four of them proved repellent action against the female adults of Cx.

pipiens.

The highest repellency was achieved by Grapefruit oil (RC50 = 0.082 g), while the lowest one was for Mandarin oil (RC50 =0,366 g).

Limonene showed RC50 value accounted to 0.448 g.

Gas chromatographic analyses of the six used oils revealed that Limonene was the dominant compound with an occurrence ranging from 51.97 % in Sour Orange oil to 95.32 % in Lime oil.

It was concluded that Limonene alone has a basic biocidal properties against the tested insect, but its potency can be improved considerably when being in the oil extracted from citrus peels.