Clausena anisata and Dysphania ambrosioides essential oils: from ethno-medicine to modern uses as effective insecticides

Dysphania ambrosioides (L.) Mosyakin & Clemants (Amaranthaceae) and Clausena anisata (Willd.) Hook. f. ex Benth. (Rutaceae) are two aromatic species traditionally used in Cameroon to repel and kill insects. The present work was carried out to substantiate this traditional use and to evaluate the possible incorporation in commercial botanical insecticides of their essential oils (EOs). The EOs were distilled from leaves of C. anisata and aerial parts of D. ambrosioides and analyzed by gas chromatography-mass spectrometry (GC-MS). The insecticidal activity of both EOs was investigated against the filariasis vector, Culex quinquefasciatus, and the housefly, Musca domestica. As possible mode of action, the inhibition of acetylcholinesterase (AChE) by the two EOs was investigated as well. The D. ambrosioides EO was characterized by the monoterpene peroxide ascaridole (61.4%) and the aromatic p-cymene (29.0%), whereas the C. anisata EO was dominated by the phenylpropanoids (E)-anethole (64.6%) and (E)-methyl isoeugenol (16.1%). The C. anisata EO proved to be very toxic to third instar larvae of C. quinquefasciatus showing LC₅₀ of 29.3 μl/l, whereas D. ambrosioides EO was more toxic to adults of M. domestica showing a LD₅₀ of 51.7 μg/adult. The mixture of both EOs showed a significant synergistic effect against mosquito larvae with LC₅₀ estimated as 19.3 μl/l, whereas this phenomenon was not observed upon application to M. domestica adults (LD₅₀ = 75.9 μg/adult). Of the two EOs, the D. ambrosioides one provided a good inhibition of AChE (IC₅₀ = 77 μg/ml), whereas C. anisata oil was not effective. These findings provide new evidences supporting the ethno-botanical use of these two Cameroonian plants, and their possible application even in synergistic binary blends, to develop new eco-friendly, safe and effective herbal insecticides.

The use of Clausena anisata in insect pest control in Africa: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Clausena anisata is used traditionally by various communities across Africa against pests such as mosquitoes, flies and weevils among others. Pests are a major cause of disease and production losses in various crop and livestock production systems in Africa. This review discusses the available information on the occurrence, chemistry, biological activity and possible commercialization of Clausena anisata with a view to see the plant species being integrated in pest management.

MATERIALS AND METHODS

Information on the ethnomedical use, chemistry and biological activity of C. anisata published between 1980 and 2016 was accessed from various databases namely Science Direct, Springer Link and Wiley Online Library. In addition various relevant books were also consulted.

RESULTS

The crude extracts as well as different fractions of C. anisata have been evaluated for activity against various insect pests and have been shown to be active. Furthermore, close to 50 compounds have been isolated and identified from C. anisata, which include coumarins, carbazole alkaloids, limonoids and essential oils (monoterpenes). Some of these compounds have been proven to exhibit pesticidal properties in both laboratory and field studies against various pests including mosquitoes, flies and weevils. The possible mechanisms of action of these compounds have been explored in this review.

CONCLUSION

The results of pesticidal and phytochemical screening of C. anisata strongly indicate that the species is endowed with pesticidal properties that can be harnessed into commercial products. However, one glaring challenge in the evaluation of this plant species for pesticidal activity has been the non-availability of standard testing systems. Researchers have used various methods which they developed based on their own circumstances and resources. Formulation, standard appropriate testing systems and agronomic research are key in unlocking the potential of this important African species.

Isolation of seselin from Clausena anisata (Rutaceae) leaves and its effects on the feeding and development of Lucilia cuprina larvae may explain its use in ethnoveterinary medicine

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves of Clausena anisata are used traditionally to expel maggots from wounds of animals in Zimbabwe. We have previously proved in the laboratory that the plant certainly affects the behaviour and growth of blowfly larvae. The objective of this study was to isolate and identify the active compounds responsible for this activity.

MATERIALS AND METHODS

The acetone extract of Clausena anisata leaf powder was separated by solvent-solvent partition into five fractions. The n-hexane fraction was the most active in the larvicidal assay and therefore subjected to open column chromatography on silica gel.

RESULTS

The isolated compound was identified by nuclear magnetic resonance (NMR) and mass spectroscopy (MS) as the pyranocoumarin, seselin, chemically known as 2',2'-dimethylpyranocoumarin. It inhibited feed intake in the first and second instars of blowfly larvae at the minimum concentration tested of 1 ppm resulting in significant lower mass pupae (13.5±0.5 mg and 22.4±0.4 mg for the first and second instar larvae respectively) compared to the solvent control group (26.19±0.8 mg) (p<0.05).

CONCLUSIONS

This is the first report of the isolation of seselin from the leaves of Clausena anisata and the first report of the compound having an effect against blowfly larvae.