The present study compares the in vitro efficacy of four chemical acaricides, viz. amitraz, coumaphos, deltamethrin and lindane, against Rhipicephalus (Boophilus) annulatus and Haemaphysalis bispinosa ticks based on adult immersion tests. Amitraz, at 350 ppm, elicited 29.2 ± 4.17% mortality against R. (B.) annulatus, 100% inhibition of fecundity and absence of hatching of eggs laid by treated ticks. The same compound at 300 ppm caused 62.5 ± 12.5% mortality against H. bispinosa, 96.7% inhibition of fecundity and complete blocking of eclosion. The LC value of amitraz against susceptible H. bispinosa was 181 ppm. Deltamethrin at 400 ppm, elicited 25.0 ± 4.81% adult R. (B.) annulatus mortality, 97.5% inhibition of fecundity and absence of egg hatching. Complete blocking of egg hatching was observed even at 30 ppm. However, deltamethrin (at 50 ppm) elicited 75.0 ± 10.76% mortality against H. bispinosa, 65.8% inhibition of fecundity and very low egg hatching (10%). The LC for deltamethrin against susceptible H. bispinosa was 33.8 ppm. Coumaphos at 50 ppm, caused mortality of 70.8 ± 4.17% with R. (B.) annulatus whereas 100% mortality was observed against H. bispinosa. The LC values of coumaphos against R. (B.) annulatus and H. bispinosa were 9 and 8.75 ppm, respectively. Complete inhibition (100%) of fecundity was observed even at 30 ppm against both parasites. Complete blocking of egg hatching was also observed even at 10 ppm of coumaphos. Lindane at 1000 ppm caused mortality of 87.5 ± 7.98% against R. (B.) annulatus and 83.3% mortality against H. bispinosa at 100 ppm. The LC values of lindane against R. (B.) annulatus and H. bispinosa were 157 and 8.61 ppm, respectively. Complete inhibition of fecundity was observed with R. (B.) annulatus treated with lindane above 200 ppm and with H. bispinosa at a concentration above 50 ppm. Complete blocking of egg hatching was observed in R. (B.) annulatus, even at 100 ppm. Lindane caused 100% blocking of egg hatching at 1 ppm in the case of H. bispinosa.
Using adult immersion test, the acaricidal activity of ethanolic extracts of leaves of Cassia alata L. was studied against Rhipicephalus (Boophilus) annulatus. The efficacy was assessed by measuring per cent adult mortality, inhibition of fecundity and hatching rate. The ethanolic extract of C. alata produced a concentration dependant increase in the adult tick mortality. The highest mortality (45.8%) and inhibition of fecundity (10.9%) were observed at the highest concentration tested (100 mg/ml). The plant extract did not affect egg hatchability.
Acaricidal effects of fipronil against Rhipicephalus (Boophilus) annulatus were studied in vitro using adult immersion test. A concentration-dependent increase in adult mortality was observed. At a concentration of 1 ppm, there was 100% inhibition of fecundity. Complete blocking of hatching of the laid ova was observed even at 500 ppb. Based on probit analysis, the 50% lethal concentration value was calculated as 12.78 ppm, which was much higher than the previously reported values against Rhipicephalus (Boophilus) microplus.
Plants constitute a rich source of bioactive compounds and its acaricidal effect is increasingly been investigated as a potential solution against acaricide resistance. In the present study, the in vitro efficacy of crude ethanolic extract of leaves of Sphaeranthus indicus, its fractions (hexane, chloroform, butanol and water) and subfractions of the active acaricidal fraction were evaluated against Rhipicephalus (Boophilus) annulatus using the adult immersion technique (AIT). The percentage of adult mortality, inhibition of fecundity and hatching rate were assessed. The crude ethanolic extract of leaves of Sphaeranthus indicus revealed hundred per cent adult mortality and inhibition of fecundity at a concentration of 250 mg/mL. Among the four fractions of this extract tested, hexane fraction showed concentration dependent delayed adult tick mortality. At 10 per cent concentration of hexane fraction, 87.41 per cent mortality and 77.78 per cent inhibition of fecundity were observed. Among the 14 subfractions of the active hexane fraction, the subfraction 4 (at 2000 ppm) produced 45.83 per cent mortality and 41.06 per cent inhibition of fecundity. It may be concluded that the hexane fraction of the leaves of ethanolic extract of S. indicus and its subfraction 4 revealed significant acaricidal effects.
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