Phytochemical induction by herbivores could affect quality of essential oils from aromatic plants

Plant tissues may show chemical changes following herbivory. In aromatic plants such changes could affect the specific compounds on which commercial exploitation is based. This possibility was analyzed for Mintosthachys mollis, a member of the Lamiaceae native to Central Argentina with medicinal and aromatic uses in the region, and two types of insect herbivores: a leaf miner and a gall insect. Analysis of the essential oils of mined/undamaged leaves, as well as leaves from stems with and without galls, revealed changes in concentrations of the two main monoterpenes. A decrease in pulegone concentration was associated with both types of insect damage, whereas menthone increased significantly only in mined leaves. Inducible chemical changes in aromatic and medicinal plants may be common and widespread; their economic implications deserve investigation.     

Composition and anti-insect activity of essential oils from Tagetes L. species (Asteraceae, Helenieae) on Ceratitis capitata Wiedemann and Triatoma infestans Klug

Essential oils from four species of the genus Tagetes L. (Asteraceae, Helenieae) collected in Tucuma?n province, Argentina, were evaluated for their chemical composition, toxicity, and olfactory activity on Mediterranean fruit fly Ceratitis capitata Wiedemann adults and for repellent properties on Triatoma infestans (Klug) (Chagas disease vector). Yields of essential oils range from 0.2 to 0.8% (v/w). The same main constituents among Tagetes minuta L., Tagestes rupestris Cabrera, and Tagetes terniflora Kunth, (cis-trans)-ocimenes, (cis-trans)-tagetones, and (cis-trans)-ocimenones showed important differences in their relative compositions. Tagetes filifolia Lag. was characterized by the recognized phenylpropanoids methylchavicol and trans-anethole as the main components. LD(50) was ≤20 μg/insect in topical bioassays. T. rupestris was the most toxic to C. capitata females, whereas the other oils presented similar toxicities against males and females. Tagetes rupestris oil attracted both sexes of C. capitata at 5 μg, whereas T. minuta showed opposite activities between males (attractant) and females (repellent). Oils from T. minuta and T. filifolia were the most repellent to T. infestans. The results suggest that compositions of essential oils influence their insecticidal and olfactory properties. The essential oils from Tagetes species show an important potential as infochemical agents on insects' behaviors. This study highlights the chemical variability of essential oils as a source of variation of anti-insect properties.     

Evaluation of micropropagation for the introduction into cultivation and conservation of Lippia junelliana, an endemic aromatic plant from Argentina

The aims of this work were to introduce Lippia junelliana into cultivation, to compare the essential oil accumulation between cultivated and wild plants, and to reintroduce micropropagated plants in the location of the original population. The leaves and inflorescences of cultivated plants accumulated, on a dry weight basis, higher amounts of essential oil than their wild counterparts. Thus, total essential oil accumulation of cultivated plant parts was also significantly higher than that of wild counterparts. The cultivated plants showed the same essential oil profile than the wild plants. This work demonstrates that cultivation can be a more efficient vehicle to both preserve and exploit L. junelliana, than collection from the wild, because higher yields of biomass and oil accumulation can be achieved, while essential oil composition is less affected by the different treatments. The reintroduction of new plants into the species’ original location has proved to be a viable alternative for their in situ preservation or enrichment planting. This model of introduction of aromatic plants into cultivation through micropropagation could be a useful technique to recover valuable chemotypes from the wild in the search for new alternatives in the agriculture and for the preservation of natural resources for future generations.     

Fumigant toxicity of essential oils against Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae): a systematic review and meta-analysis

Our aim was to perform a qualitative review and a meta-analysis with 57 scientific articles (108 assays) published from 1 January 2000 to 31 June 2021 dealing with fumigant toxicity of essential oils (EOs) against Sitophilus zeamais. The studies were obtained from four electronic databases: Web of Science, SCOPUS, PubMed, and Google Scholar. The survey comprised 107 plant species belonging to 26 different families. Lethal concentration values (LC₅₀) of EOs were included in a random-effect model, and two subgroups were defined: “until 24 h” and “more than 24 h”. The EOs more frequently evaluated were those belonging to Lamiaceae (20.18%), Asteraceae (17.43%), Apiaceae (9.17%), and Rutaceae (6.42%). The global mean value was 21.37 (CI₉₅ 16.84–27.12), while the summary mean values of the subgroups were 41.45 (CI₉₅ 31.10–55.26) for “until 24 h” and 8.45 (CI₉₅ 5.72–12.48) for “more than 24 h”. Most species belonging to Apiaceae, Lamiaceae, Asteraceae, and Schisandraceae reported the highest insecticidal effects with mean values that ranged from 1.31 to 27.39 for “until 24 h” and from 0.57 to 5.31 for “more than 24 h”. Additionally, the toxicity of the most effective EOs was discussed by addressing their chemical composition and their major pure compounds chemical features.

     

Effects of thymol and isoeugenol feed supplementation on quail adult performance,egg characteristics and hatching success

1. A study was conducted to evaluate whether feed supplementation with thymol or isoeugenol can alter Japanese quail growth rate and final body weight, the female onset of puberty, hen-day egg production and the physical and chemical characteristics of the egg, as well as its potential to alter hatchability.

2. From 4 to 16 weeks of age, birds from each cage (1 male: 3 females) were assigned to 1 of 3 treatments that differed in the supplement added to the feed: control, thymol or isoeugenol (400?mg/kg). The average ages (d) at first egg lay (FIRST), at 25% egg production (A25% EP), at 50% egg production (A50% EP) and weekly and cumulative hen-day egg production (HDEP) were calculated. In addition, physical and chemical characteristics of the eggs, their fertility and hatchability were also evaluated for each group.

3. Feed supplementation did not significantly affect growth rate, final body weight, egg production parameters, fertility and physical characteristics of egg or most of the fatty acid components of the yolk.

4. The group treated with isoeugenol showed an increase in the percentage of palmitoleic fatty acid compared to the control, with thymol group showing intermediates values.

5. Both thymol and isoeugenol supplemented groups showed increased hatchabilities, by 18·8% and 11·8%, respectively, compared to their control counterparts.

6. The improvement in the hatching success of the eggs from the thymol and isoeugenol supplemented groups without a negative impact on their performance may have important economic implications for future breeding programmes, particularly if these effects generalise from quail to other more commercially important poultry species, such as chickens or turkeys.     

Quantitative variations in the essential oil of Minthostachys mollis (Kunth.) Griseb. in response to insects with different feeding habits

Plants display a diverse array of inducible changes in secondary metabolites following insect herbivory. Herbivores differ in their feeding behavior, physiology, and mode of attachment to the leaf surface, and such variations might be reflected in the induced responses of damaged plants. Induced changes were analyzed for Minthostachys mollis, a Lamiaceae with medicinal and aromatic uses, and four species of folivore insects with different feeding habits (chewing, scraping, sap-sucking, and puncturing). In M. mollis leaves experimentally exposed to the insects, levels of the two dominant monoterpenes pulegone and menthone were assessed 24 and 48 h after wounding. Menthone content generally decreased in the essential oil of damaged leaves, whereas pulegone concentration increased in all treatments. These changes occurred also in the adjacent undamaged leaves, suggesting a systemic response. The relatively uniform response to different kinds of damage could be attributable to the presence of such a strongly active compound as pulegone in the essential oil of M. mollis. The effects of wounding on essential oil concentration may be significant from a commercial point of view.     

Anticholinesterase and pediculicidal activities of monoterpenoids

The repetitive and inadequate application of pediculicidal products frequently results in the development of resistance to these compounds. Essential oils are a promising alternative to synthetic insecticides, although their mode of action remains to be explored. It has been proposed that one possible target of the essential oils is the inhibition of acetylcholinesterase (AChE). The role of monoterpenoids as possible AChE inhibitors and their relationship with the toxicity was investigated both in vitro and in vivo. Inhibition of electric eel AChE activity showed that the most effective inhibitor was 1,8-cineole with IC(50) 6 x 10(-3) M. The inhibition of AChE activity of head louse homogenate by 1,8-cineole showed IC(50) 7.7 x 10(-2) M. The intoxication symptoms of head lice exposed to vapors of 1,8-cineole was recorded before the in vivo head louse AChE inhibition assay. No correlation was found between neurotoxic symptoms and inhibition of AChE activity.