Effects of essential oils on native and recombinant acetylcholinesterases of Rhipicephalus microplus.

This study reports the action of essential oils (EO) from five plants on the activity of native and recombinant acetylcholinesterases (AChE) from Rhipicephalus microplus. Enzyme activity of native susceptible AChE extract (S.AChE), native resistant AChE extract (R.AChE), and recombinant enzyme (rBmAChE1) was determined. An acetylcholinesterase inhibition test was used to verify the effect of the EO on enzyme activity. EO from Eucalyptus globulus, Citrus aurantifolia, Citrus aurantium var.dulcis inhibited the activity of S.AChE and R.AChE. Oils from the two Citrus species inhibited S.AChE and R.AChE in a similar way while showing greater inhibition on R.AChE. The oil from E. globulus inhibited native AChE, but no difference was observed between the S.AChE and R.AChE; however, 71% inhibition for the rBmAChE1 was recorded. Mentha piperita oil also inhibited S.AChE and R.AChE, but there was significant inhibition at the highest concentration tested. Cymbopogon winterianus oil did not inhibit AChE. Further studies are warranted with the oils from the two Citrus species that inhibited R.AChE because of the problem with R. microplus resistant to organophosphates, which target AChE. C. winterianus oil can be used against R. microplus populations that are resistant to organophosphates because its acaricidal properties act by mechanism(s) other than AChE inhibition.

Effects of essential oils on native and recombinant acetylcholinesterases of Rhipicephalus microplus / Efeito de óleos essenciais sobre acetilcolinesterases nativa e recombinante de Rhipicephalus microplus

Abstract This study reports the action of essential oils (EO) from five plants on the activity of native and recombinant acetylcholinesterases (AChE) from Rhipicephalus microplus. Enzyme activity of native susceptible AChE extract (S.AChE), native resistant AChE extract (R.AChE), and recombinant enzyme (rBmAChE1) was determined. An acetylcholinesterase inhibition test was used to verify the effect of the EO on enzyme activity. EO from Eucalyptus globulus, Citrus aurantifolia, Citrus aurantium var.dulcis inhibited the activity of S.AChE and R.AChE. Oils from the two Citrus species inhibited S.AChE and R.AChE in a similar way while showing greater inhibition on R.AChE. The oil from E. globulus inhibited native AChE, but no difference was observed between the S.AChE and R.AChE; however, 71% inhibition for the rBmAChE1 was recorded. Mentha piperita oil also inhibited S.AChE and R.AChE, but there was significant inhibition at the highest concentration tested. Cymbopogon winterianus oil did not inhibit AChE. Further studies are warranted with the oils from the two Citrus species that inhibited R.AChE because of the problem with R. microplus resistant to organophosphates, which target AChE. C. winterianus oil can be used against R. microplus populations that are resistant to organophosphates because its acaricidal properties act by mechanism(s) other than AChE inhibition.

Resumo Este estudo relata a ação de óleos essenciais de cinco plantas na atividade de acetilcolinesterases (AChE) nativas e recombinantes de Rhipicephalus microplus. A atividade enzimática do extrato de acetilcolinesterase nativa suscetível (S.AChE) e resistente (R.AChE) e da enzima recombinante (rBmAChE1) foi determinada. Um teste de inibição da AChE foi utilizado, para verificar o efeito dos óleos essenciais sobre a atividade enzimática. Óleos essenciais de Eucalyptus globulus, Citrus aurantifolia, Citrus aurantium var. dulcis inibiram a atividade de S.AChE e R.AChE. Os óleos das duas espécies de Citrus inibiram S.AChE e R.AChE de maneira semelhante, mas mostraram maior inibição sobre R.AChE. O óleo de E. globulus inibiu a AChE nativa, mas sem diferença entre a S.AChE e a R.AChE; no entanto, 71% de inibição para rBmAChE1 foi observada. O óleo de Mentha piperita também inibiu S.AChE e R.AChE, mas houve inibição significativa apenas nas concentrações mais altas testadas. O óleo de Cymbopogon winterianus não inibiu a AChE. Estudos adicionais são necessários com os óleos das duas espécies de Citrus que inibiram a R.AchE, devido ao problema de R. microplus resistente aos organofosforados ter como alvo AChE. O óleo de C. winterianus pode ser usado contra populações de R. microplus, que são resistentes a organofosforados, porque suas propriedades acaricidas agem por mecanismos diferentes.

In-vitro efficacy of a botanical acaricide and its active ingredients against larvae of susceptible and acaricide-resistant strains of Rhipicephalus (Boophilus) microplus Canestrini (Acari: Ixodidae).

Ticks and tick-borne diseases are a major constraint for a sustainable cattle industry in the tropical and subtropical regions of the world. The development of resistance to most of the commonly used acaricides has led to an assessment of herbal products for acaricidal activity as an eco-friendly tick control alternative. A botanical product, Essentria® IC-3 insect concentrate containing rosemary oil (10%), geraniol (5%) and peppermint oil (2%), acts on target pests by blocking octopamine. Essentria® IC-3 and its active components were evaluated for larvicidal activity against several susceptible and acaricide-resistant strains of the cattle fever tick, Rhipicephalus (Boophilus) microplus Canestrini by Larval Packet test using 14-21 d old unfed larvae. The efficacy was assessed by measuring percent larval mortality and estimating lethal concentrations at 50% (LC50) and 95% (LC95) with 95% confidence limits (CL) using probit analysis. The LC50 and LC95 (95% CL) values for Essentria® IC-3 against the susceptible strain were estimated as 0.647% (0.59-0.69) and 1.033% (0.94-1.19), respectively, whereas, LC50 and LC95 values for other strains were variable, ranging from 0.597-1.674% and 0.927-2.236%, respectively. Among the various active ingredients, the larvicidal property of Essentria® IC-3 seem to be attributable mainly to geraniol and the LC50 and LC95 (95% CL) values for geraniol against the susceptible Deutch strain were estimated as 0.656% (0.61-0.69) and 1.114% (1.03-1.25), respectively. The comparison of LC50 and LC95 values of acaricide-resistant strains showed susceptibility comparable to Deutch against geraniol except for the Las Palmas strain. We report a low level of resistance in some of the acaricide-resistant strains against the herbal acaricide in the cattle tick for the first time, possibly due to cross-resistance to chemical acaricides.

In vitro repellency of DEET and ß-citronellol against the ticks Rhipicephalus sanguineus sensu lato and Amblyomma sculptum.

Rhipicephalus sanguineus sensu lato and Amblyomma sculptum can parasite humans and domestic animals and are vectors of pathogens, including zoonoses. Repellents are an important tool of tick control. This study aimed to compare the efficacy of N,N-diethyl- 3-methylbenzamide (DEET), a standard repellent, versus ß-citronellol in a Petri dish bioassay. A semicircle of filter paper (31.8cm2) was treated with 87µl of one of four concentrations (0.200, 0.100, 0.050 and 0.025mg/cm2) of ß-citronellol, DEET or solvent (ethanol). A head-to-head test was developed treating one side with increasing concentrations of ß-citronellol as above mentioned, against the highest concentration of DEET. Besides that a blank assay was performed. Three males and three females were placed in the middle of the plate and their location was evaluated 5, 10 and 30min after the test was initiated. As a result, the time had no significant effect on repellency response of the ticks exposed to both compounds and their concentrations. The repellency response raised according with the increase of concentration. Additionally, our findings indicate that the tick A. sculptum was more sensitive to the compounds tested and ß-citronellol showed a higher efficacy than DEET. In addition, ß-citronellol could be formulated to protect humans and other animals from R. sanguineus s. l. and A. sculptum infestation, as well as the diseases transmitted by these species.