Lethal toxicity of Achillea millefolium and Marrubium vulgare extracts, against potato tuber moth, Phthorimaea operculella (Lepidotera, Gelechiidae) in comparison with some synthetic pesticides

Nowadays, use of botanical compounds as pesticides is becoming increasingly important, because of their acceptable efficiency and relative safety to human and environment. The present study aimed to investigate oral toxicity of different extracts of Achillea millefolium L. and Marrubium vulgare L., against larvae of potato tuber moth and compare their potency with some conventional insecticides. Larvae of potato tuber moth, reared on potato tubers in controlled conditions. Extraction was carried out by maceration method using hexane, ethyl acetate, methanol and water as solvents. Foliage of A. millefolium and M. vulgare collected, well washed with distilled water, air dried in shadow then used for extraction. For bioassays fresh potato leaves dipped in each concentration of extracts for 5 seconds, air dried for 20 minutes. Potato tuber moth larvae transferred on treated leaves. Mortality was recorded after 48 hours. The results revealed that, aqueous and ethyl acetate extracts of A. millefolium showed the most and the least toxicity against 1st larval instar, with LC50 values of 2.96 and 44.03 gr/lrespectively. Methanol extract of A. millefolium and ethyl acetate extracts of M. vulgare were more and less toxic against 2nd larval instar of PTM with LC50 values of 9.03 and 34.79 gr/l, respectively. The toxicity comparison of plants extracts with Fenvalerate, Imidacloprid and Acetamiprid showed that, in all cases the synthetic pesticides were more toxic than plant extracts. Acetamiprid with LC50 values of 0.18 and 0.31 gr/l was more toxic than other pesticides against 1st and 2nd larval instars of PTM, respectively but relative potency of plant extracts was comparable with Fenvalerate.