Caio Márcio de Oliveira Monteiro

Heterorhabditis amazonensis (Rhabditidae: Heterorhabditidae), strain RSC-5, for biological control of the cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

The aim of this study was to evaluate the influence of different doses of Heterorhabditis amazonensis RSC-5 on the biological parameters of engorged females of Rhipicephalus (Boophilus) microplus. The female ticks, individually identified, were divided into six groups of 20 each and exposed to the following nematode concentrations: 0, 75, 150, 300, 600, and 1,200/female. The following parameters were observed: initial weight, final weight, alteration weight, egg mass weight, pre-oviposition period, oviposition period, survival period, incubation period, hatching percentage, reproductive efficiency index (REI), nutritional efficiency index (NI), and percentage of control. There were no significant differences observed for the initial weight, pre-oviposition period, incubation period, and NI (p > 0.05) between the various treated groups and the control group. However, there were significant differences (p < 0.01) for the oviposition and survival periods between all the treated groups and the control group. For the final weight, alteration weight, egg mass weight, and REI, only the treatment with 1,200 nematode/female did not differ significantly from the respective figures for the control group (p > 0.05). The highest control rate was 67.8%, obtained in the treatment with a concentration of 300 entomopathogenic nematodes/female. The results demonstrate that this nematode has a deleterious effect on the majority of the biological parameters analyzed.

Evaluation of the action of Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae) isolate HP88 on the biology of engorged females of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

The objective of this work was to evaluate the effect of different concentrations of the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora strain HP88 on the biological parameters of the non-parasite phase of engorged females of the cattle tick Rhipicephalus (Boophilus) microplus. Six groups were formed, each containing 20 engorged females, which were exposed to the following concentrations of infective juveniles of this nematode: 0, 75, 150, 300, 600 and 1200 EPNs/female, respectively. The following biological parameters were observed: female weight before oviposition, egg mass weight, pre-oviposition period, oviposition period, survival period, hatching percentage, egg production index (%EPI), nutritional index (%NI) and efficacy of treatment. There were no statistically significant differences in the female weight before the oviposition and pre-oviposition period (p>0.05) between the groups. The nematode action caused significant alterations (p<0.01) in the egg mass weight, oviposition period, survival period, hatching percentage, %EPI and %NI between the treated groups and the control group. Treatment efficacy was higher than 90% in all groups, reaching 99% at a dosage of 1200 EPNs/female. The present study demonstrates that under laboratory conditions, H. bacteriophora HP88 has a deleterious effect on the majority of the parameters of the non-parasitic phase of engorged R. (B.) microplus females, making this species a potential biological control agent of cattle ticks.

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.

Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae) HP88 for biological control of Rhipicephalus microplus (Acari: Ixodidae): the effect of different exposure times of engorged females to the nematodes.

The aim of this study was to assess the influence of different exposure times of engorged female the Rhipicephalus microplus to infective juveniles of Heterorhabditis bacteriophora isolate HP88. The engorged females were divided into seven groups (six treatments and one control) of 20 ticks each with statistically similar average weights (p>0.05) and exposed to concentrations of 300 nematodes/tick for periods of 3, 6, 12, 24, 48 and 72 h. The following biological parameters were monitored: pre-oviposition period; egg mass weight; hatching percentage; and efficacy of treatment. There was no influence of the exposure time on the pre-oviposition period (p>0.05), while there were significant differences (p<0.05) between the groups exposed for 24, 48 and 72 h and the control group with respect to the egg mass weight, and 24h for hatching percentage. Treatment efficacy reached 100% after exposure for 48 and 72 h. These results demonstrate that infective juveniles of H. bacteriophora HP88, under laboratory conditions, interfere in the majority of the biological parameters of the non-parasitic phase of engorged R. microplus females when the exposure time is greater than or equal to 24h.

Entomopathogenic nematodes in insect cadaver formulations for the control of Rhipicephalus microplus (Acari: Ixodidae)

This study evaluated the efficacy of four entomopathogenic nematode (EPN) strains in insect cadaver formulations against Rhipicephalus microplus and compared the efficacy of the most virulent EPNs applied in cadavers of Galleria mellonella and Tenebrio molitor. In the first experiment, infected G. mellonela larvae were used as the source of EPNs. Engorged females of R. microplus were placed in pots filled with soil and different numbers of G. mellonella larvae infected with one of four species of nematodes. All treatments with EPNs of the genus Heterorhabditis caused significant reduction (p<0.05) in the egg mass weight and hatching percentage of larvae. The EPNs of the genus Steinernema, except for the group exposed to Steinernema carpocapsae ALL, whose source nematodes included six larvae of G. mellonella, caused a significant reduction (p<0.05) in the egg mass weight produced per female. Steinernema feltiae SN applied with two, four, and six cadavers and S. carpocapsae ALL with two cadavers caused a reduction in hatching percentage of larvae of R. microplus (p<0.05). The percentage of control was above 95% in all groups treated with Heterorhabditis bacteriophora HP88 and Heterorhabditis indica LPP1 and in the treatment with four larvae infected with S. feltiae SN. The second experiment followed the same methodology, using G. mellonella and T. molitor larvae infected by the two most virulent EPNs. H. bacteriophora HP88 and H. indica LPP1 in different formulations caused reduction in the egg mass weight and hatching percentage of larvae. The percentage of control were 82.4 and 84.9% for H. bacteriophora HP88 and H. indica LPP1, respectively, formulated in T. molitor, and reaching 99.9% in groups formulated with G. mellonella. The EPNs tested in insect cadaver formulation showed pathogenicity to engorged females of R. microplus and EPNs of the genus Heterorhabditis formulated in G. mellonella larvae were more effective.

Acaricidal activity of methanol extract of Acmella oleracea L. (Asteraceae) and spilanthol on Rhipicephalus microplus (Acari: Ixodidae) and Dermacentor nitens (Acari: Ixodidae)

We evaluated the acaricidal activity of Acmella oleracea methanol extract and spilanthol on Rhipicephalus microplus and Dermacentor nitens. The extract was made through maceration with methanol. From this extract, a dichloromethane fraction with 99% spilanthol was obtained and tested on R. microplus larvae and engorged females and D. nitens larvae. For evaluation against larvae, the modified larval packet test was used, and both the methanol extract and dichloromethane fraction were tested at concentrations of 0.2-50mg/mL. The modified larval packet test was also used in the lethal time (LT) test, with the methanol extract at a concentration of 12.5mg/mL and the percentage mortality was assessed after 15, 30, 45, 60, 75, 90, 120min and 24h. The 50% lethal time calculation (LT50) was performed in this test. The engorged female test was performed with R. microplus only, at concentrations of 25-200mg/mL for methanol extract and 2.5-20.0mg/mL for spilanthol. The methanol extract caused 100% mortality of the R. microplus and D. nitens larvae at concentrations of 3.1 and 12.5mg/mL, respectively. Spilanthol resulted in 100% mortality of R. microplus larvae at concentration of 1.6mg/mL and of D. nitens at 12.5mg/mL. In the lethal time assay using the methanol extract, the mortality rate was 100% for R. microplus and D. nitens larvae after 120min and 24h, with LT50 values of 38 and 57min, respectively. In the test of females, the egg mass weight and the hatching percentage of the groups treated with concentrations equal to or higher than 50.0mg/mL of methanol extract were significantly reduced (p<0.05), while for spilanthol, the reduction of the egg mass weight and hatching percentage occurred from concentrations of 10.0mg/mL and 2.5mg/mL, respectively. Females treated with 200.0mg/mL of extract died before starting oviposition, resulting in 100% effectiveness, while the best efficacy for spilanthol was 92.9% at a concentration of 20.0mg/mL. Thus we conclude that the methanol extract of A. oleracea and spilanthol have acaricidal activity against R. microplus and D. nitens.