Toxic effect of Callistemon viminalis essential oil on the ovary of engorged Rhipicephalus microplus female ticks (Acari: Ixodidae).

Rhipicephalus microplus is the main ectoparasite of cattle and its parasitism can reduce weight gain of hosts, in addition to causing anemia, increasing the risk of myiasis, and resulting in the transmission of Babesia bovis and Anaplasma marginale, among other pathogens. The use of synthetic chemicals plays an important role in controlling these ticks. However, its frequent and indiscriminate use has contributed to the selection of resistant strains, resulting in greater interest in the search for natural-origin products. The shrub Callistemon viminalis (Myrtaceae), also known as weeping bottlebrush, is known for its antibacterial, acaricidal, repellent, and antifungal activities, but there are no reports in the literature about its effects on the internal morphology of ticks. This study aimed to extract and characterize the essential oil obtained from the leaves of C. viminalis. Additionally, its effects on the ovary morphology of engorged R. microplus were assessed through histological, histochemical, and morphometric techniques. Exposure to C. viminalis caused dose-dependent morphological changes, such as cellular alterations in the epithelial layer lining the ovary lumen and the pedicel, irregularity of the chorion and oocyte shape, changes in protein and carbohydrate content, decrease in oocyte size, reduction in the size of the nucleus as well as cytoplasmic and nucleolar vacuolation. Thus, C. viminalis essential oil exhibited a toxic effect on the reproductive system of R. microplus, which may result in the reproductive impairment of this tick species.

Active packaging of poly(lactic acid) nanofibers and essential oils with antifungal action on table grapes.

The table grape is a non-climateric fruit that is very susceptible to fungal contamination, in addition to suffering an accelerated loss of quality during storage. The in vitro and in grape antifungal and antiocratoxigenic effects of the essential oils from Alpinia speciosa and Cymbopogon flexuosus against Aspergillus carbonarius and Aspergillus niger were studied. The oils were encapsulated in poly(lactic acid) (PLA) nanofibers as a potential active packaging to be applied to control the degradation of grapes stored during the post-harvest period. Fungal proliferation and ochratoxin A synthesis in A. carbonarius and A. niger decreased in the presence of the active packaging. However, the nanofiber containing the essential oil from C. flexuosus was more efficient in providing a fungicidal effect against A. carbonarius (10% and 20%) and A. niger (20%). In addition, weight loss and color changes were controlled and the parameters of acidity, °Brix, softening and the texture of the grape were maintained. A very small mass loss of the essential oils encapsulated in nanofibers was observed by thermogravimetric analysis, showing that the nanofiber was efficient in enabling the controlled release. The quality and safety of table grapes were maintained for longer periods of storage in the presence of active packaging, so the incorporation of these oils in nanofibers can be a promising way to increase the shelf life of grapes.

Effect of the essential oils of Satureja montana L., Myristica fragrans H. and Cymbopogon flexuosus S. on mycotoxin-producing Aspergillus flavus and Aspergillus ochraceus antifungal properties of essential oils.

Essential oils can be a useful alternative to the use of synthetic fungicides because they have biological potential and are relatively safe for food and agricultural products. The objectives of the present study were to evaluate the antifungal and antimycotoxigenic activities of the essential oils from Satureja montana L., Myristica fragrans H. and Cymbopogon flexuosus S. against Aspergillus flavus and Aspergillus ochraceus, as well as their effects on ergosterol synthesis and membrane morphology. The antifungal potential was evaluated by mycelial growth analysis and scanning electron microscopy. Fungicidal effects against A. flavus, with MFC of 0.98, 15.62 and 0.98 µL/mL, respectively, were observed for the essential oils from S. montana, M. fragrans and C. flexuosus. Aspergillus ochraceus did not grow in the presence of concentrations of 3.91, 15.62 and 0.98 µL/mL of the essential oils from S. montana, M. fragrans and C. flexuosus, respectively. The essential oils significantly inhibited the production of ochratoxin A by the fungus A. ochraceus. The essential oils also inhibited the production of aflatoxin B1 and aflatoxin B2. The biosynthesis of ergosterol was inhibited by the applied treatments. Biological activity in the fungal cell membrane was observed in the presence of essential oils, given that deleterious effects on the morphologies of the fungi were detected. The essential oils under study are promising as food preservatives because they significantly inhibit toxigenic fungi that contaminate food. In addition, the essential oils hindered the biosynthesis of mycotoxins.

Acaricidal and repellent activity of the essential oils of Backhousia citriodora, Callistemon viminalis and Cinnamodendron dinisii against Rhipicephalus spp.

The ticks Rhipicephalus microplus and Rhipicephalus sanguineus sensu lato (s.l) are of great importance to agriculture, veterinary medicine and public health. Due to a number of problems related to the use of synthetic acaricides, natural products emerge as promising substances for alternative tick control. In the present study, essential oils of Backhousia citriodora, Callistemon viminalis and Cinnamodendron dinisii were extracted by hydrodistillation, characterized by GC-MS and GC-FID and biologically evaluated for acaricidal activity against R. microplus and repellent activity against R. sanguineus s.l. Inhibition of acetylcholinesterase (AChe) by the essential oils was also evaluated. The major constituent of B. citriodora is citral (98.9 %), whereas the essential oil from C. viminalis is rich in 1.8-cineole (78.1 %), α-pinene (12.5 %) and limonene (3.36 %), and that from C. dinisii contains α-pinene (30.8 %), ß-pinene (12.5 %) and sabinene (11.3 %) as the principal constituents. The median lethal concentrations (LC 50) estimated for the essential oils on engorged R. microplus females were 3.276 µL.mL-1 for B. citriodora, 8.195 µL.mL-1 for C. dinisii and 8.936 µL.mL-1 for C. viminalis. The essential oil of B. citriodora showed the best repellent effect against unfed R. sanguineus s.l. adults, demonstrating repellent action up to 3 h after application. The essential oil of C. viminalis was able to reduce AChe activity, with an average inhibitory concentration (IC 50) of 0.33 µg mL-1. Thus, these oils can be considered as sources of bioactive compounds for tick control.

Cytotoxic effects of Satureja montana L. essential oil on oocytes of engorged Rhipicephalus microplus female ticks (Acari: Ixodidae).

In addition to pesticidal activity, the capacity of natural compounds to inhibit the reproduction of parasites emerge as an important alternative tick control method. In this context, Satureja spp. stand out due to their recognized pesticidal properties. Among parasites of veterinary importance, the cattle tick, Rhipicephalus microplus, is responsible for great economic losses in livestock and transmission of relevant pathogens. Thus, the aim of this study was to evaluate the effects of different concentrations of the essential oil of Satureja montana L. on the ovary morphology of R. microplus engorged females through histological and histochemical techniques. The most remarkable morphological changes found were: cytoplasmic vacuolation of germ cells, irregular and thicker chorion, irregular oocyte shape, ring-shaped nucleolus, decrease in protein and carbohydrate content in oocytes, in addition to cellular changes in the oviduct and pedicel. All morphological changes were assessed using a semiquantitative method already established in the literature. Ticks exposed to 5.0 µl/ml of essential oil showed the most significant changes when compared to control groups. Thus, the essential oil of S. montana L. damaged the reproductive system of R. microplus, which may impair ticks' offspring production and promote a long-term control of this species. HIGHLIGHTS: The essential oil of Satureja montana L. affects the ovary morphology of the cattle tick. The main morphological alterations found were cytoplasmic vacuolation, irregular and thicker chorion and irregular oocyte shape. These alterations may impair the development of eggs.