Résumé
ABSTRACT The excessive use of chemical insecticides has led to negative effects on human health and the environment. Volatile oils are one of the possible potential alternatives to chemical insecticides. Traditionally Seriphidium brevifolium (Wall. ex DC.) Ling & Y.R.Ling, Asteraceae, powder from its leaves is used to treat gastric problems and expel intestinal worms by local peoples, but yet there is no literature available regarding its insecticidal activity. In this study fumigant toxicity and enzyme inhibition activities of the S. brevifolium volatile oil collected from the highlands of Skardu Baltistan, Pakistan, was evaluated against the red imported fire ant Solenopsis invicta. The phytochemical studies indicated that monoterpenes were the most abundant constituents, accounting for 88% of the total oil. The major dominant constituents were 2-bornanone (28.2%), 1,8-cineole (19.9%), α-thujone (7.5%), β-thujone (6.7%) which accounts for 62.3% of total constituents identified, with volatile oil yield of 4.11% (w/w). The fumigation assay indicated that the volatile oil was acutely toxic to fire ants, with an LC50 of 16.47 µl/l. Among the constituents tested, only (α + β) thujone and 1,8-cineole were toxic, with LC50 of 17.68 and 30.66 µl/ after 12 h of exposure. The volatile oil, (α + β) thujone and 1, 8-cineole showed strong fumigant activity against the red imported fire ant workers in a time- and dose-dependent manner. The volatile oil caused 100% mortality of the red imported fire ant workers, even at the lowest concentration of 20 µl/l after 24 h of exposure. In addition, the volatile oil and 1,8-cineole inhibited acetylcholinesterase activity, while (α + β) thujone inhibited carboxylesterase activity in the fire ant workers. It has been concluded that the volatile oil and some of the compounds from S. brevifolium might be developed as eco-friendly approaches for the control of red imported fire ants.
Résumé
Objective: Black bean aphid (Aphis fabae) is one of the most important greenhouse and crop pests with a wide range of hosts, which causes damages through feeding on vegetable sap and transmitting viral diseases. Currently, chemical methods are mainly used to control this pest. Considering the adverse effects of pesticides, it is essential to apply less chemical pesticide in pest control programs. The lethal and sublethal effects of the essential oil (EO) of Teucrium polium leaves on one-day-old adults of black bean aphid were investigated under laboratory conditions. Method: The bioassay was evaluated at the concentrations of 0.88−12 µL/L air, for 24 h after treatment. Reproductive life table parameters of new emerged aphid surveyed at sub-lethal concentrations (LC20 and LC40) of EO and the biological reproductive table was calculated by Jackknife method. Results: The mortality rate increased significantly with the increasing of EO concentration. The estimated LC50 value was 4.5 µL/L air. Laboratory exposure to sublethal concentrations of EO caused significant decrease in adult female longevity and fertility of surviving aphids and as a result caused significant reduction in the intrinsic rate of natural increase (rm value). Conclusion: The results of this study revealed that EO of T. polium could be used as a potential control agent for the aphid.