ENTOMOPATHOGENIC NEMATODES: AN INTEGRATED APPROACH
IN CONTROL OF TICKS
Sudha Rani. R*, Diagnostic Parasitology, SRDDL, IAH&VB, Hebbal,
Bangalore-24
Mahanthesh M T, Scientist ( Animal Science ), University of Agricultural Sciences, Raichur
ABSTRACT
Ectoparasites are widely distributed in all agro-ecological zones of tropical countries like India. Among livestock, large and small ruminants are the most affected by ectoparasites of veterinary importance, hindering their productivity. The indiscriminate use of synthetic acaricides at frequent intervals has led to the development of resistance in ticks causing toxic manifestations in animals, human safety, residual effect on meat and milk and environmental hazards. Never days pest bio control agents are far more environment friendly than chemical pesticides. Among bio control agents, Entomopathogenic Nematodes (EPN’s) have received much attention due mainly to their potential as biopesticides against insect pests, and agricultural pests. Therefore, the need of biological control of tick’s gains importance and EPN’s holds a promising future for tick control. This review throws light on the mechanism of EPN’s on ticks, diagnostic methods in knowing the efficacy of Entomopathogenic Nematodes as a Biocontrol of ticks. Many researchers have found Entomopathogenic nematodes of the genus Steinernema and Heterorhabtiditis were effective against few species of ticks by bio assay test. In our study two EPN species i.e Heterorhabditis indica and Steinernema abbasi were tested against ticks i.e Haemaphysalis, Rhipicephalus and Hyalomma spp by bioassay test. It was found that among two EPNs used, H.indica were effective against ticks than S.abbasi suggesting that EPN efficiency is greatly influenced by its dose. Thus, EPNs might be used as part of an integrated approach to control tick resistant to various acaricides.
Keys words: Entomopathogenic Nematodes, Biological control, ticks.
Economic importance of ticks has long been recognized due to their ability to transmit diseases to humans and animals. Indiscriminate use of synthetic acaricides at frequent intervals leading to the development of resistance in ticks, toxic manifestations in animals, human safety, residual effect on meat and milk and environmental hazards (FAO, 2004). The desire to minimize chemical pesticides, pest bio control agents are far more environment friendly than chemical pesticides. Biological pest control usually refers to the action of parasites, predators or pathogens on a pest population which reduces its numbers below a level causing economic burden.Biological control of pathogens includes bacteria, fungi and parasitic wasps.
NEMATODE – TICK INTERACTION: Entomopathogenic nematodes (EPN’s) are widely distributed throughout the world and have been isolated from many types of natural and managed habitats in a wide variety of soils. EPNs serve as vectors of bacteria, which achieve quick kill of the target pest and thus have high potential capability in integrated pest management. EPN’s of the genus Heterorhabditis (Rhabditida: Steinernematidae, Heterorhabditidae) are symbiotically associated with bacteria of genus Xenorhabdus and Photorhabdus (Enterobacteriaceae). The life cycle of both Heterorhabditis and Steinernema species comprises of non-feeding, free living infective free living juveniles (IJ) that infects the insect host in the soil environment and develop into adult life stage. The infective juveniles of third stage are the only free-living stage that persists in the soil in search of a susceptible arthropod host. Once the EPN enters the cuticle and or natural openings (i.e., mouth, anus and spiracles), the Infective Juvenile’s (IJs) release the symbiotic bacteria into the insect haemocoel, multiply and kill the host, usually within 24-48hrs.
Entomopathogenic nematode’s feed on symbiotic bacteria and complete three generations in the host cadaver. As food resources are depleted, new IJs are produced and disperse in search of the new hosts. But tick mortality caused by EPNs seems to be due to the rapid proliferation of the nematode symbiotic bacteria within the ticks, since the nematodes do not go through their natural cycle within ticks.
VIRULENCE OF EPN TO TICKS: The susceptibility of ticks to infection by EPNs will vary according to tick species, stage of ticks to EPN’s (Samish et al.,2008). The fully engorged female ticks are most susceptible whereas the preimaginal stages are least sensitive, while the eggs were fully resistant (Samish and Glazer 1991). The engorged females seek environments with high moisture and protected from solar radiation at time of oviposition, a condition that also favours the survival of EPNs (Grew et al.,2001). There are many factors that influence the efficacy that EPN would have in a given system including host species, host life stage, nematode species and strain (Mauleon et al. 1993; Samish et al. 1999a), and nematode dose or concentration (Vasconcelos et al. 2004).
In -vitro EFFICACY METHODS: Many researchers have evaluated the efficacy of EPN’s under laboratory conditions for the control of ticks by bioassay experiments as described by Vasconcelos et al., (2004) where in the mortality of ticks was recorded after 24hrs of application of EPNs on engorged ticks. Further the effect was also evaluated by reproductive biology assay to check the effectiveness of EPNs on engorged tick by recording the weight of engorged ticks before oviposition, egg mass weight, hatching per centage, egg production index and effectiveness of EPNs in per centage control.
An bio assay study conducted at Dept of Veterinary Parasitology, KVAFSU, Bangalore we noticed that among the two EPN species tested, Heterorhabditis indica and Steinernema abbasi was most virulent on engorged female tick species of Haemaphysalis, Rhipicephalus and Hyalomma. Apart from the bio assay test, reproductive potentiality of EPN against ticks with different parameters i.e., egg mass weight, hatching per cent, egg production index and percentage of control was recorded. We observed reduction in the number of eggs produced by engorged females at the highest concentrations of H.indica and S.abbasi along with reduced hatchability, reduced egg production index and percentage control. The increase in concentration of the EPNs might be attributed to the increased penetration of infective juveniles into the haemocoel which contributes to the establishment of the infection process which aids EPNs to overcome the host’s immune barriers. So there by the increase in concentration of EPN’s resulted in decreased values for all parameters evaluated.
Many researchers found that EPNs were found successfully to control different insect pests (Grewal et al., 2001) and different species of ticks (Samish et al., 2008). Thirteen ixodid tick species and two argasid species were susceptible to nematodes where adults being the target stage (Samish et al., 2000). Most of the research studies have been directed toward the control of R. microplus (Vasconcelos et al., 2004) and Rhipicephalus annulatus (Glazer et al., 2001; Alekseev set al., (2006) and also against R.sanguineus, R.haemaphysaloides by Hussain et al. (2016). In some studies, application of EPNs shown effective against Amblyomma americanum, Ixodes ricinus (Hartelt et al.2008), Dermacenter nitens (Monteiro et al.2014). These in-vitro efficacy studies of EPNs under laboratory conditions on ticks by many researchers suggest that EPNs is an promising biological agents can be used as part of an integrated approach to control of ticks.
CONCLUSION: The EPNs will not undergo their normal propagative cycle within ticks (Zhioua et al. 1995) thereby supporting the hypothesis that ticks are poorer nematode hosts than insects. The genetic diversity of EPN strains suggests that antitick virulence could be further increased by screening, selection and genetic manipulation. The ecological habitats of nematodes and off-host tick stages are often similar thereby increasing its potential in control of ticks stages present in animal sheds. The biological control of pest is often based on certain biocontrol agents that target different species and stages are more efficient in specific ecological habitats or seasons which can replace chemical pesticides. Thus, the inclusion of EPNs in an integrated tick-control program can be of immense help and it should be considered seriously.
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