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The aim of this study was to evaluate the circadian and seasonal variation of Ageratum conyzoides essential oil (EO) and its nematicidal effect on the free-living nematode Caenorhabditis elegans as a model for parasitic helminths. For the seasonal study, the plants were collected from January to December 2022, at 6 a.m., and to assess the circadian rhythm, the plants were collected in April (rainy season) and October (dry season), at 6, 9, 12 a.m. and 3 and 6 p.m. The fresh plants were then subjected to hydrodistillation, and their chemical composition was analyzed using gas chromatography coupled with mass spectrometry (GC-MS). The motility test with C. elegans was carried out. The primary constituent of the oils was precocene I (65.97 to 78.42 %, respectively), followed by E-caryophyllene (6.04 to 12.16 %), comprising an average of 79.87 % of the composition throughout the year. The average yields of EOs were slightly higher in the rainy season, at 0.68 %, compared to the dry season, at 0.62 %. High light hours in the rainy season (12 a.m., 0.96 %) and in the dry season (9 a.m., 0.88 %) seem to contribute to higher daily oil yields. It was observed that the variation between the main constituents of A. conyzoides occurs in inverse proportion when analyzing the main classes of compounds present in the oils: chromenes (CH) and sesquiterpene hydrocarbons (SH). And that the month of March had the highest content of E-caryophyllene (12.16 %) when compared to the other months of the year. On the other hand, January and December had the lowest levels of precocene I (65.97 and 66.85 %). The IC 50 of the EO of A. conyzoides varied according to the month and time of collection. The EO obtained in January was the most effective against C. elegans, with an IC 50 of 0.01 mg/mL. Thus, A. conyzoides EO could be an alternative for nematode control, exhibiting greater efficacy if extracted during specific seasonal periods., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Rhipicephalus microplus is an important cattle tick, and resistant strains to synthetic compounds have been widespread. The combined effects of different essential oil compounds enhance biological activity and reduce selection for the development of target organism resistance. Essential oils of two different genotypes of each of Lippia sidoides and Lippia gracilis and their main components, the isomers thymol and carvacrol, have acted as acaricides against R. microplus. Little is known about the effects of the essential oils of L. sidoides and L. gracilis and thymol and carvacrol on the morphophysiology of R. microplus ovaries. This study aimed to identify the morphological changes in the ovaries of R. microplus females treated with essential oils from two different genotypes of each of L. sidoides (102 and 103) and L. gracilis (106 and 201) and the terpenes thymol and carvacrol through histological techniques. The LC 50 and LC 75 of essential oils and thymol and carvacrol were used for Adult Immersion Test (AIT) with groups of five fully engorged females of R. microplus. A negative control (DMSO 3% solution) was performed. Seven days after the AIT, the ticks were dissected to collect ovaries and their histologic analysis. Only the group treated with the essential oil of L. gracilis genotype 106 at the LC 50 had no change compared with the control. The other groups showed the following changes in oocytes I to V: vacuolation, chorion deformation, disorganization of yolk granules, and irregularities at the cell periphery, causing incomplete process of vitellogenesis. Thus, the essential oils tested in this study may be potent products for the control of cattle ticks and thereby preventing further life cycles., (Copyright © 2021 Elsevier B.V. All rights reserved.)