Acaricidal activity of Havardia albicans and Caesalpinia gaumeri methanolic leaf extracts on Rhipicephalus microplus and its toxicity to laboratory animals.

The acaricidal activity of methanolic extracts from the leaves of Havardia albicans (Kunth Britton and Rose) and Caesalpinia gaumeri (Greenm) were tested on the larvae and adults of the cattle tick Rhipicephalus microplus Canestrini using the larval immersion test and the adult immersion test, respectively. The toxicity of these extracts was also evaluated on laboratory animals using toxicity bioassays at different concentrations: skin irritability (500 mg/ml), acute oral toxicity (5000 mg/kg), ocular irritability (1000 mg/ml) and dermal toxicity (5000 mg/kg). The acaricidal activity of the H. albicans extracts on R. microplus larvae showed a LC50 of 7.0% (4.3-11.4) and a LC99 of 25.5% (14.26-201.5). The acaricidal activity of the C. gaumeri extracts on larvae showed a LC50 of 7.8% (5.74-10.65) and a LC99 of 38.32% (22.22-146.48). The H. albicans extracts showed moderate acaricidal activity in the inhibition of egg laying (54.4 ± 12.4) and the inhibition of larval hatching (48.7 ± 6.8) in R. microplus adults. The C. gaumeri extracts also showed moderate acaricidal activity in the inhibition of egg laying (51.0 ± 11.2). However, none of the evaluated extracts showed significant toxicity on laboratory rodents. These plants show the potential to control R. microplus and could be administered topically or orally in animals. Further studies are needed to identify the active compound(s) and to evaluate the effects of these plants on R. microplus in vivo.

Acaricidal activity of Mexican plants against Rhipicephalus microplus resistant to amitraz and cypermethrin.

This study evaluates the acaricidal activity of Mexican native plants against a Rhipicephalus microplus population resistant to both amitraz and cypermethrin. To explore the activities of plants, the larvicidal effects of 72 Kupchan fractions (Hex, DCM, AcOEt and MeOH:H2O) of 18 plant species collected in Veracruz, Mexico were studied. The evaluation of the Kupchan fractions against double resistant R. microplus indicated that the fractions of Annona globiflora (Hex, LC50 = 0.007% w/v; DCM, LC50 = 0.007% w/v), Annona scleroderma (Hex, LC50 = 0.08% w/v; DCM, LC50 = 0.02% w/v), and Litchi chinensis (Hex, LC50 = 0.79% w/v; DCM, LC50 = 0.54% w/v) showed the greatest larvicidal activities. To identify the presence of additive, synergistic, or antagonistic effects, the acaricidal activity of binary mixtures of the most active fractions of A. globiflora, A. scleroderma, L. chinensis and Citrus sinensis were also evaluated. The latter was chosen as it is easy to obtain due to its substantial presence in agricultural activity locally and globally. The results showed synergistic interaction of the fraction Hex of C. sinensis with the fractions of Hex and DCM of L. chinensis. The most active larvicidal fractions were tested against engorged ticks of R. microplus by adult immersion test at concentration of 2.5% w/v. The Hex and DCM fractions from A. globiflora and A. scleroderma were the most active, causing 100% mortality. The Hex and DCM fractions of L. chinensis exhibited approximately 50% mortality, while the other evaluated fractions did not show efficacy at this concentration. Therefore, it is evident that the fractions of these plants have the potential to be used in either combined or single form as effective alternatives in the control of R. microplus zoonoses.