Erik Daemon

Acaricidal activity of thymol on larvae and nymphs of Amblyomma cajennense (Acari: Ixodidae).

The aim of the present study was to evaluate the acaricidal efficacy of thymol on unengorged and engorged larvae and engorged nymphs of Amblyomma cajennense. To perform the test for unengorged larvae, the larval packet technique was employed and mortality was evaluated 24h after the test, while for engorged larvae and engorged nymphs the immersion technique was employed and mortality was evaluated after 15 days. In all the experiments, the following concentrations of thymol were tested: 2.5, 5.0, 10.0, 15.0 and 20.0mg the thymol/ml. The control group was exposed to water and 1% DMSO and there were 10 repetitions for each treatment. The values found for mortality of unengorged larvae were 18.2%, 51.8%, 97.6%, 93.5% and 94.5%, and for engorged nymphs the values were 26.0%, 92.2%, 100.0%, 100.0%, 100.0%, in concentrations of 2.5, 5.0, 10.0, 15.0 and 20.0mg of thymol/ml, respectively. In the test with engorged larvae, mortality was 100.0% in all treatments. Based on the results, it is possible to conclude that thymol has acaricidal activity against immature stages of A. cajennense.

A new approach to characterization of the resistance of populations of Rhipicephalus microplus (Acari: Ixodidae) to organophosphate and pyrethroid in the state of Minas Gerais, Brazil

The monitoring of resistance of cattle tick populations in Brazil to the chemical bases in use is largely limited to investigation of the phenotypic profile. There are few studies investigating the role played by the genotypic profile in acaricide resistance in the country. Therefore, the aim of the present study was to carry out molecular characterization and trace out the genetic profile of populations of Rhipicephalus microplus with respect to resistance to the organophosphate and pyrethroid chemical groups. For that purpose, larvae were genotyped belonging to 587 populations for pyrethroids and 306 for organophosphates, using the polymerase chain reaction technique. It was found that 75.49% and 97.44% of the larvae studied showed resistance to the organophosphates and pyrethroids, respectively. Among the populations resistant to pyrethroids, 91.9% were heterozygotes, showing that most of the resistant populations have only one allele responsible for resistance. Therefore, it is possible to conclude that the genotyped populations have high resistance to organophosphates, and even more so to pyrethroids. This information is fundamental for understanding the mechanisms of resistance of R. microplus to acaricides, to enable improvement of control techniques.

Acaricidal activity of hydroethanolic formulations of thymol against Rhipicephalus sanguineus (Acari: Ixodidae) and Dermacentor nitens (Acari: Ixodidae) larvae

The aim of this study was to assess the acaricidal activity of hydroethanolic formulations of thymol at varying concentrations on Rhipicephalus sanguineus and Dermacentor nitens larvae. The larval packet test was used and the thymol concentrations tested were 2.5, 5.0, 10.0, 15.0 and 20.0 mg/ml. The control group was exposed only to water and ethanol (50/50%) and there were 10 repetitions for each treatment. The mortality was evaluated after 24 h. For the R. sanguineus larvae, the mortality rates were 47.5, 50.2, 96.7, 95.9 and 98.1%, while for D. nitens the rates were 14.1, 75.0, 90.2, 90.3 and 99.5%, at respective thymol concentrations of 2.5, 5.0, 10.0, 15.0 and 20.0 mg/ml. The results indicate that the hydroethanolic formulations of thymol tested have acaricidal activity on R. sanguineus and D. nitens larvae exposed topically, causing mortality greater than 90% 24 h post-treatment starting at the concentration of 10 mg/ml.

Avaliação da atividade repelente do timol, mentol, salicilato de metila e ácido salicilico sobre larvas de Boophilus microplus (Canestrini, 1887) (Acari: Ixodidae)

The repellent activity of thymol, menthol, salicylic acid and methyl salicylate on Boophilus microplus larvae was studied. These substances were tested according to their solubility: emulsions in 1% aqueous dimethylsulphoxide or in pure water. Three concentrations were tested for each substance, 1.0%, 0.5% and 0.25%, with five repetitions for each. Approximately 100 larvae at 21 days of age were placed on the base of wooden sticks and then observed for repellent action every two hours, during twelve hours. The results obtained from the higher concentrations showed that the four substances caused alterations on the larvae behavior. However, thymol (65% of mortality and 35% of repellency), menthol (80% of repellency) and methyl salicylate (80% of repellency) were the most efficient.

Ectoparasites of Nasua nasua (Carnivora, Procyonidae) from an urban forest in Southeastern Brazil

Em um fragmento de mata na area urbana de Juiz de Fora (MG) foram capturados 15 quatis com armadilha e ceva, para estudo dos seus ectoparasitos. Outros quatro animais, atropelados no entorno, foram tambem examinados imediatamente apos o atropelamento, e incluidos na analise. Os ectoparasitos foram removidos com a utilizacao de pinca e pente-fino e acondicionados em etanol 70°GL. Pulgas e piolhos foram clarificados e montados para analise em microscopia. Os ixodideos foram identificados sob estereoscopia. Nao foram encontrados carrapatos adultos. Larvas e ninfas de carrapatos foram encontradas, respectivamente, em 36,8% e 63,1% dos hospedeiros examinados. Ninfas que sofreram muda foram identificadas como Amblyomma cajenennse. A especie de piolho Neotrichodectes pallidus foi obtida em 52,6% dos quatis. As pulgas Ctenocephalides felis felis e Rhopalopsyllus lutzi lutzi apresentaram, respectivamente, as seguintes prevalencias: 36,8% e 35,1%. O estudo mostra que no fragmento de mata na area urbana os quatis podem manter especies de ectoparasitos comuns a estes hospedeiros, bem como intercambia-las entre o ambiente silvestre e urbano.

Evaluation of the combined effect of thymol, carvacrol and (E)-cinnamaldehyde on Amblyomma sculptum (Acari: Ixodidae) and Dermacentor nitens (Acari: Ixodidae) larvae

This study aimed at assessing the combined effect of thymol, carvacrol and (E)-cinnamaldehyde on Amblyomma sculptum and Dermacentor nitens larvae. The effects resulting from treatments were evaluated by means of the modified larval packet test. In order to determine the LC50, components of essential oils, the monoterpenes thymol, carvacrol and phenylpropanoid (E)-cinnamaldehyde were individually tested at different concentrations. After determining the LC50, each essential oil component was separately evaluated and then combined with another substance at a 1:1 proportion at the LC50 concentration and at 1/2 and 1/4 of the LC50. For A. sculptum, the lowest LC50 value was obtained for (E)-cinnamaldehyde (1.40 mg/ml), followed by thymol (2.04 mg/ml) and carvacrol (3.49 mg/ml). The same order of effectiveness was observed for D. nitens, with values of 1.68, 2.17 and 3.33 mg/ml, respectively. In the evaluation of component associations of essential oils against A. sculptum larvae, only the combinations between carvacrol and thymol (LC50) and carvacrol and (E)-cinnamaldehyde (1/4 LC50) presented a moderate synergetic effect. In turn, for D. nitens larvae, the combinations between thymol and carvacrol (LC50 and 1/2 LC50) presented a synergetic effect, while the others presented an additive or antagonistic effect. Therefore, it can be concluded that the combination of thymol and carvacrol (LC50) has a moderate synergetic effect against A. sculptum larvae, while thymol, combined with carvacrol (LC50 and 1/2 LC50), has a synergetic effect against D. nitens larvae.

Acaricidal activity of essential oil from Lippia sidoides on unengorged larvae and nymphs of Rhipicephalus sanguineus (Acari: Ixodidae) and Amblyomma cajennense (Acari: Ixodidae).

The aims of this work were to identify the compounds and to investigate the acaricidal activity of the essential oil of Lippia sidoides for unengorged larvae and nymphs of Rhipicephalus sanguineus and Amblyomma cajennense. The oil was analyzed by gas chromatography and gas chromatography/mass spectrometry. In total, 22 compounds comprising 98.5% of the total peak area were identified. The major constituent of the essential oil was thymol (69.9%). The acaricidal activity against larvae and nymphs was assessed using a modified larval packet test. In all experiments, oils were tested at concentrations of 2.35, 4.70, 9.40 14.10 and 18.80 mg/mL. The mortalities of larvae and nymphs of R. sanguineus were 20.6, 47.8, 73.6, 99.5 and 99.0% and 12.0, 50.0, 76.3, 96.0 and 96.1%, respectively. For larvae and nymphs of A. cajennense the rates of mortality were 41.9, 63.3, 77.8, 82.5 and 100.0% and 0.0, 32.8, 64.8, 71.1 and 94.0%, respectively. The LC 90 values of the L. sidoides oil were 11.56 and 12.97 mg/mL for larvae and nymphs of R. sanguineus and 15.70 and 18.52 mg/mL for larvae and nymphs of A. cajennense, respectively. The essential oil from L. sidoides has acaricidal activity on unengorged larvae and nymphs of R. sanguineus and A. cajennense.

Prevalência e variação dos estádios eritrocíticos do Plasmodium (Novyella) juxtanucleare em Gallus gallus sob condições naturais, no período de um ano

The avian malaria caused by Plasmodium juxtanucleare in Gallus gallus, is a tipical plasmodiose from Brazilian gallinaceous. This disease can causes morbidy and mortality in its vertebrate hosts. This work was conducted at Boa Vista farm, Municipality of Santa Barbara do Tugurio, Minas Gerais, Brazil and the ours objectives were to evaluate the hight prevalence found in previous studies and to accompany the variation of the erytrocytic forms during one year. The bloods smears, dyed with Giemsa were examined in microscopy immersion. Twenty five half-breed fowls were accompany duting one year, monthly (from November/00 to May/01) and biweekly (from June/01 to October/01). The erytrocytic forms were registered and quantified by the observation of 100 microscopic fields. Was verified a prevalence of 100% by P. juxtanuclerare, but there wasn’t statistics correlation between the increase of the erytrocytic forms during the year. The trophozoites were the more abundant form found in this studie.

Experimental infestation with the immatures of Amblyomma dissimile Koch, 1844 (Acari: Ixodidae) on Tropidurus torquatus (Lacertilia: Iguanidae) and Oryctolagus cuniculus

Larvas provenientes de duas femeas de Amblyomma dissimile Koch, 1844 (Acari: Ixodidae), naturalmente ingurgitadas em uma iguana (Iguana iguana) e provenientes do Estado do Mato Grosso, foram utilizadas na infestacao experimental de lagartos da especie Tropidurus torquatus e coelhos domesticos. As larvas alimentadas em ambos os hospedeiros realizaram ecdise para ninfas. As ninfas apenas ingurgitaram no lagarto e mudaram para machos e femeas. Este e o primeiro registro do parasitismo de larvas e ninfas de A. dissimile em T. torquatus e de larvas em coelhos.

Synergism of thymol, carvacrol and eugenol in larvae of the cattle tick, Rhipicephalus microplus, and brown dog tick, Rhipicephalus sanguineus.

The effects of combinations of the monoterpenes thymol and carvacrol and the phenylpropanoid eugenol in larvae of Rhipicephalus microplus (Canestrini, 1888) (Acari: Ixodidae) and Rhipicephalus sanguineus sensu lato (s.l.) (Acari: Ixodidae) were assessed by the larval packet test. The CompuSyn program was used to make qualitative assessments of the effects (synergistic, additive and antagonistic) of the associations. The effects of all combinations tested against R. microplus larvae were synergistic, with combination indices (CIs) <0.70. When tested against R. sanguineus, eight of the mixtures showed a synergistic effect (CI < 0.70); only the carvacrol + thymol mixture at LC50 presented a moderate synergistic effect, with CIs between 0.70–0.90. This study is the first to determine the effects of the interactions of these substances in the control of these two tick species. The combinations of carvacrol + thymol, carvacrol + eugenol and thymol + eugenol have synergistic effects in R. microplus and R. sanguineus s.l. larvae.