Larvicidal, molluscicidal and nematicidal activities of essential oils and compounds from Foeniculum vulgare

Plant-based products, namely essential oils (EOs), are environmentally friendly alternatives for the control of disease vectors, hosts and/or parasites. Here, we studied the general toxicity and biopesticidal potential of EOs and phenylpropanoids from Foeniculum vulgare var. vulgare (bitter fennel), a perennial plant well adapted to temperate climates. EO/compound toxicity was tested against a freshwater snail and potential intermediate host of Fasciola hepatica (Radix peregra), a mosquito and former European malaria vector (Anopheles atroparvus) and one of the most damaging plant-parasitic nematodes, the root-knot nematode (Meloidogyne javanica). Lethal concentrations (LC50; LC90) of EOs (infrutescences/stems with leaves) and compounds were calculated by probit analysis. All displayed noteworthy activity against R. peregra adults (LC50 21-39 A mu g ml(-1)) and A. atroparvus larvae (LC50 16-56 A mu g ml(-1)). trans-Anethole revealed acute nematicidal activity after 24 and 48 h (LC50 310 and 249 A mu g ml(-1), respectively), and estragole (1,000 A mu g ml(-1)) showed some effectiveness against M. javanica hatching and juveniles after 15 days. Plant and EO yields were determined to evaluate the bitter fennel productivity. The chemical composition of the EOs was analyzed by gas chromatography coupled to mass spectrometry. EOs extracted from whole plants, infrutescences and stems with leaves were characterized by estragole-dominant profiles (28-65 %), considerable amounts of phellandrene (10-34 %) and fenchone (6-16 %), and minor trans-anethole contents (1-4 %). Although additional toxicological studies against nontarget organisms are required, our study demonstrates that bitter fennel is a productive source of molluscicides and larvicides, and thus a potential sustainable biological agent to control particular host species, namely freshwater snails and mosquitoes.We would like to thank Jose Ferreira and Diara Rocha from the IHMT for the mosquito colony maintenance and larvae production and collaborators from the Nematology Laboratory of the University of Coimbra for kindly providing the nematode isolate. The authors are grateful to Susana Chaves for improving the use of English in the manuscript. This research was supported by FEDER through POFC-COMPETE and by Portuguese funds through the projects (PIDDAC)-PEst-OE/BIA/UI4050/2014 and PEst-OE/AGR/UI4033/2014. R.M. Sousa was supported by the Portuguese Foundation for Science and Technology (FCT) through a PhD grant (SFRH/BD/66041/2009).info:eu-repo/semantics/publishedVersio

Plant essential oils and formamidines as insecticides/acaricides: what are the molecular targets?

The parasitic mite Varroa destructor is the main cause of the severe reduction in beekeeping during the last few decades. Therefore, efforts have been made to develop chemical treatments against the parasite. In the past, synthetic products were preferentially used to combat Varroa mites. Nowadays, mainly plant essential oils and organic acids are applied because they are safer and impose less unfavorable effects on the environment. Essential oils contain mixtures of mostly volatile and odorous terpenoid constituents. The molecular targets of these substances are tyramine and/or octopamine receptors that control and modulate vital functions ranging from metabolism to behavior. Disturbing the native function of these receptors in the mite results in deleterious effects in this parasite. This overview considers not only tyramine and octopamine receptors but also other potential targets of essential oils including ionotropic GABA(A) receptors, TRP type ion channels, and acetylcholinesterase