Ticks are known to be a nuisance in the animal production sector and serve as vectors for several diseases of human, livestock and pets. In animals, tick infestations are much more severe than in humans. However, the prevalence of soft ticks is comparatively lower and wherever they are present they cause severe economic loss by sucking the blood of animals. Acaricides form the center of control and eradication efforts; however, their long term use has generated acaricide resistance among ticks. Commercially available preparations of 1.25% EC deltamethrin and 10% EC cypermethrin were used for assessment of their acaricidal activity against soft ticks; Ornithodoros spp. by using Larval Packet Test. The commercial preparations of both the pyrethroides (deltamethrin and cypermethrin) failed to show complete mortality either at the manufacturer’s recommended dosage or at highest concentration employed in this study. The study revealed that there is an urgent need to study the acaricidal resistance status of soft ticks prevalent in different areas and as per result obtained.
Ticks distributed worldwide, parasitizing on mammals, birds and reptiles, are obligate blood sucker and are of enormous veterinary relevance owing to the direct damage they cause to their hosts (Telmadarraiy et al., 2007). At the same time they are vectors of large variety pathogens (Matias et al., 2007; Bouwknegt et al., 2010). They are most competent and versatile arthropod vector for transmission of various pathogens in animals as well as humans (Shyma et al., 2015a). Prevalence of soft ticks is comparatively lower than that of the other hard tick and also they act as a vector for comparatively fewer pathogens. It is therefore, due to this reason these ticks garner little less attention of the livestock keepers for their control. However, these ticks are significant blood suckers and cause huge production loss. Massive numbers of ticks will feed on the lower legs of their hosts and toxins in the tick’s saliva can cause paralysis and a toxaemia which is sometimes fatal (Walker et al., 2014). Acaricides form the center of control and eradication efforts because they offer relatively quick and cost-effective suppression of tick populations (Abbas et al., 2014). Long term use, however, has generated acaricide resistance in many tick species (Shyma et al., 2014, 2015a; Guerrero et al., 2014, Shyma et al., 2015b). Therefore it is important to investigate the efficacy of commonly used acaricides to control ticks so as to check their resistant or susceptible status and formulation of new control methods in case of treatment failure. Very few reports are available on susceptibility/resistance status of soft ticks (Ghavami et al. 2015; Sharma et al., 2017). The present investigation was targeted to study the acaricidal effect of some of the commercially available acaricides (deltamethrin and cypermethrin) on buffalo soft ticks of Banaskantha district of North Gujarat.
Materials and Methods
Tick Collection and Laboratory Maintenance
The ticks were collected from Deesa taluka of the Banaskantha district which is in the northwestern part of Gujarat, at latitudes, longitudes and altitudes of 24.2585° N, 72.1907° E and 144.58 Meters at sea level, respectively. Annual ambient temperature and rainfall of the study areas were in the range of 11.8° C, through 41.5° C, and 221 mm, respectively. Live engorged adult female ticks were handpicked under close scrutiny from all kinds of surfaces including cervices and cracks on the walls of cattle and buffalo shelters, human dwellings, and indoor caves. Ticks were kept in vials covered with muslin cloth were brought to Entomology Laboratory, Department of Veterinary Parasitology, Sardarkrushinagar Dantiwada Agricultural University, Sardarkrushinagar, Gujarat, India. Identification of ticks was done both by gross examination and with a microscope using tick identification sources (Ruedisueli and Manship, 2006; Telmadarraiy et al., 2004; Walker et al., 2014). Ticks were then washed, cleaned, labeled, and kept for egg laying at 28 ± 1˚C and 85 ± 5% relative humidity. Ticks were kept up to two months for hatching of eggs into larvae. Further, larvae were kept for 12–14 days before performing experimental bioassay.
Commercial Synthetic Pyrethroids
The commercial products, namely 1.25% EC deltamethrin at the concentrations of 12.5, 25, 50, 100 and 200 ppm and 10% EC cypermethrin 100, 200, 400, 800 and 1600 ppm respectively, were prepared in distilled water from the stock solution.
Larval Packet Test (LPT)
Larval packet test was conducted according to FAO (1971), guidelines with minor modifications (Shyma et al., 2015a). A number of 3.75 cm by 8.5 cm filter paper rectangles (Whatman filter paper no. 1) were impregnated with six hundred microlitres of different concentrations of deltamethrin and cypermethrin in distilled water. The impregnated paper was dried by keeping the same for 30 minutes in an incubator at 37˚C. The rectangles were folded in half to form an open-ended packet and sealed on the sides with adhesive tapes, to place tick larvae. Approximately 100 larvae were inserted and the packet was sealed with adhesive tape. Total three packets filled with larvae were kept for each concentration of drugs. These packets were then placed in desiccators in BOD incubator maintained at 28 ± 1˚C and 85 ± 5% RH. The packets were removed after 24 h, and larval mortality was calculated after counting the number of live and dead larvae. Control packets impregnated with water were also prepared for each series of concentration to be tested.
Dose–response data were analyzed by probit method (Finney, 1972). Regression curves of mortality of larva were also plotted against values of acaricide concentrations by log dosage probit mortality analysis and LC50 and LC95 values of both the synthetic pyrethroids were determined.
Results and Discussion
The morphological features particular to Ornithodoros spp. like size, oval rounded body with tough, corrugated, dusty colored integument with rounded tubercles revealed that the ticks collected were soft ticks belonging to family Ornithodoros spp. (Ruedisueli and Manship 2006; Telmadarraiy et al., 2004; Walker et al., 2003). The Scutum was absent and the mouthparts were small and ventrally placed (Fig. 1).
Fig.1: Macroscopic and microscopic view of Ornithodoros spp.
In the present study, very little mortality was recorded in the larvae of soft ticks treated with various concentrations of deltamethrin and the mean mortality varied from 0.16±0.16% to 1.95±0.42%. The slope of mortality was 0.74±0.13 whereas, the value of the coefficient of determination (R2) for developed regression equation was 0.91 (Fig. 2). Similarly, comparatively low but significant (from control), mortality was recorded in the larvae treated with various concentrations of cypermethrin and the mean mortality varied from 4.61±0.49 to 32.11±0.83%. The slope of mortality was 1.01±0.06 whereas, the value of goodness of fit (R2) was 0.99 (Fig. 2). Acaricidal effect of commercial preparations of deltamethrin and cypermethrin on Ornithodoros spp. ticks are presented in Table 1.
Table 1: Mortality, slope and coefficient of determinations of commercial formulations of deltamethrin and cypermethrin on larvae of Ornithodoros spp. ticks.
|Acaricide||Conc. (ppm)||Mean Mortality (%)||Slope||R2|
Fig. 2: Dose dependent mortality of Ornithodoros spp. against cypermethrin and deltamethrin
Soft ticks are equally important as hard ticks in the spread of infectious diseases to animals and humans and also suck blood leading to anemic condition, severe economic loss due to loss of production and stress in animals. Natural selection for resistance in tick populations is a major consequence of artificial extensive application of acaricides and a major threat to the efficacy of control programs against tick borne diseases. In the present study, the mortality of larvae of Ornithodoros spp. was very low against both deltamethrin and cypermethrin at its market recommended dosage. These chemicals could not produce cent percent mortality even in the highest concentration. Due to the lack of reference resistance or susceptible strain of Ornithodoros spp. tick, it was difficult to determine the level of resistance. In present study we have got results which indicate very high concentrations of acaricide at which 50 or 95 % mortality could be registered. There are only a few studies related to susceptibility/resistance status of Ornithodoros spp. ticks against various acaricides. In a previous study, Sharma et al. (2017) reported susceptibility of Ornithodoros spp. ticks against deltamethrin and cypermethrin, although from different area of Banaskantha district. However, this study is in contrary to the finding of Sharma et al. (2017). This further necessitates an urgent need to develop baseline information on discriminating concentration in susceptible line of Ornithodoros spp. to determine the status of susceptibility or resistance of the field population of these ticks. The present study, however, suggests the emerging resistance in soft tick against the commonly used acaricides and further study has to be undertaken to determine the mechanism of resistance in these ticks. A comparative study has been conducted by Telmadarraiy et al. (2007) for estimation of comparative susceptibility of cypermethrin in Ornithodoros lahorensis Neuman and Argas persicus Oken field populations in Iran. Comparison of the resistance ratio of collected strains with susceptible strain showed a resistance ratio of 56.7 and 2.4-folds for cypermethrin in O. lahorensis Mesh and A. persicus West Ap strains, whereas the O. lahorensis West Ol completely susceptible to cypermethrin. Ghavami et al. (2015) worked on susceptibility level of Ornithodoros tholozani to some pesticides in North West of Iran.
Different levels of resistance to deltamethrin and cypermethrin were observed in various populations of Ornithodoros spp. of Banaskantha district of Gujarat, reviewing and refining the control measures against ticks, applying new formulations of acaricide mixtures and monitoring the susceptibility level of acaricides seem necessary in these regions. Moreover, future studies to identify the molecular characteristics of resistance to acaricides and determining the effective acaricide are highly recommended in these areas.
The authors are thankful to the Director of Research and Dean, College of Veterinary Science and Animal Husbandry, Sardarkrushinagar Dantiwada Agricultural University, for providing facilities to carry out the research work.
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