Biocontrol potential of entomopathogenic nematodes against camel tick, Hyalomma dromedarii (Acari: Ixodidae)

1 Introduction

Vectors and vector borne diseases could pose a severe hazard to people, animals, and wildlife all over the world (Guglielmone et al., 2015, Dantas-Torres et al., 2012). Ticks are second-most among viral, bacterial, rickettsial, and protozoan agents compared to mosquitoes (Dantas-Torres, 2018). Ticks directly harm cattle through painful bites, blood loss, skin damage, and anorexia, which results in decreased development, in addition to serving as infection vectors (Jabbar et al., 2015). Hyalomma dromedarii (Koch, 1844) belongs to family Ixodidae (Barker and Murrell, 2004); was predominantly tick-infected Sinai (95.6 %), Sudan (89 %), and Benha and Belbis in Egypt (57.13 %) camels (van Straten and Jongejan, 1993, Elghali and Hassan, 2009, Ramadan, 1997, Al-Ghamdi et al., 2020, Ashjaran and Sheybani, 2019). It is found in semi-deserts and deserts from Saudi Arabia to northwest India (Hoogstraal, 1979). Camels are the main animals that adult H. dromedarii infect. Although cattle are also taken into consideration, camels are the primary feeders of ticks and mites. According to (FAOSTAT, 2019), Riyadh province has the greatest percentage of camels in Saudi Arabia, which is one of the countries with recent significant increase in the camel population (Faye, 2015). The country had a population of about 500,000 in 2017 (FAOSTAT, 2019). The dromedary camel is important to the economy and culture of the Arab world. Numerous illnesses have a major adverse effect on camel production; especially when there are inadequate veterinary services available (Megersa, 2010). Ticks are one of many endo- and ectoparasites that negatively impact camels' health, performance, and productivity (Megersa, 2010). Camels are infested by more than 20 species of ixodid (Hoogstraal et al., 1981, Banaja and Ghandour, 1994), and it is vital that they are actively controlled. Ticks of the genus Hyalomma are the most prominent species among them (Elghali and Hassan, 2009, Fard et al., 2012), and they may act as transmitters for Babesia spp., and Theileria spp. (El Kady, 1998, Fard et al., 2012, Al-Deeb et al., 2015, Barghash and Hafez, 2016, Alanazi et al., 2018), and Anaplasma spp. (Fard et al., 2012). However, it's still unclear whether Hyalomma spp. ticks have the ability of serving as these infections' vectors. Many factors make it difficult to control tick populations, including ticks' large egg production, multiple developmental stages, and ability to parasitize a variety of hosts (EL Roby et al., 2018). Using repellents and acaricides is a common and effective way to mitigate the threat that ticks cause to humans, animals, and livestock. Nevertheless, repeated usage and inadequate dosage of chemicals resulted in ticks developing resistance, and the cost of traditional ectoparasitic medications was exorbitant (Foil et al., 2004, Klafke et al., 2017, Monteiro et al., 2020). According to (George et al., 2008), the use of repellents and synthetic pesticides to control target pests of veterinary and medical importance became increasingly difficult. This led to adverse effects of these chemicals (acute and chronic toxicity) on the hosts and contamination of animal and plant products, including milk and meat. In Saudi Arabia, attempts had been previously made to assemble some key information on the important ectoparasites that infest camels (Camelus dromedarius). Additionally, there is a growing need for the creation of novel, chemical-free tick management techniques with a lower risk of polluting the environment, food, or animals, as well as causing human and animal intoxication (Samish, 2000). Entomopathogenic nematodes (EPNs) were one type of bio-agent explored for tick control (EL-Sadawy and Abdel-Shafy, 2007, Samish et al., 2008, Basu et al., 2012, Monteiro et al., 2014, Monteiro and Prata, 2015, EL Roby et al., 2018). With the help of mutualistic bacteria, EPNs eliminate ticks and other arthropods; Xenorhabdus and Photorhabdus species of bacteria are symbiotically linked to Steinernema and Heterorhabditis species, respectively (Gaugler and Kaya, 1990). As the only free-living stage, infective juvenile nematodes infect hosts by natural openings such as the mouth, anus, and spiracles, or sometimes through the cuticle. Once inside the host, they release their bacterial symbionts into the hemocoel, where they kill the host (Koppenhöfer et al., 2007). Engorged Rhipicephalus microplus females were vulnerable to infection by various EPN species, according to laboratory testing (Singh et al., 2018). It has been suggested in new research to use EPNs directly in pastures (Monteiro et al., 2020). Engorged females look for moist areas shielded from sunlight to oviposit in after reaching engorgement, separating from their animal host, and dropping to the ground (Chagas et al., 2001). A favorable soil microclimate is created by these circumstances, allowing EPN to survive and spread infection on engorged females. The survival and virulence of EPNs can be affected by different abiotic factors, particularly temperature, with optimal conditions varying at the species level, and even among isolates of the same species (Rohde et al., 2010). The temperature threshold at which a nematode species can survive, infect, and reproduce is generally close to the climatic conditions of its geographic origin (Molyneux and Bedding, 1984). In the same context, the isolation of native EPN as biological control agents against mosquitoes that may spread serious human diseases like yellow fever, Chikungunya, Zika, and dengue has been the subject of numerous investigations (El-Sadawy et al., 2018, Kovendan et al., 2018, Yüksel et al., 2023). The biocontrol ability of EPNs S. siamkayai, H. indica, S. glaseri, and S. abbasi against Aedes aegypti, Anopheles stephensi, and Culex quinquefasciatus larvae was assessed by (Dilipkumar et al., 2019). In the same way, (Thanwisai et al., 2022) concluded that EPN, H. indica and its symbiotic bacteria Photorhabdus are larvicidal against A. aegypti and C. quinquefasciatus mosquitoes and may serve as effective biocontrol agents. In Saudi Arabia, research on the effectiveness of EPNs against the camel tick H. dromedarii is missing or inadequate. Therefore, the objective of the current study is to assess the laboratory acaricidal activity of five isolated native EPNs against H. dromedarii.

2 Materials and methods

2.1

2.1 Tick

On the same trial day, the engorged females of tick, Hyalomma dromedarii (about 10 not parasitized ticks, homogenized in size, age, and shape per camel) were manually gathered from naturally infested camels without previous treatment with acaricides on a farm located in the city of Taif, Saudi Arabia. To verify that the gnathosoma was intact and would allow the use of surviving ticks, engorged females were examined under a stereo microscope (Fig. 1).

Close

Fig. 1

Hyalomma dromedarii engorged female.

Export to PPT

3 Results

4 Discussion

The current study's findings proved that the five isolates of EPNs at different levels and exposure times were virulent to H. dromedarii engorged females to some extent with average mortality percentage values ranged from 26.6 to 74.3 % (Table 1). A linear increase in mortality occurred with increasing IJs concentration and exposition. It was clear from the results that the Heterorhabditis spp. was more effective than S. feltiae against the engorged females under laboratory conditions, which indicates low virulence. Low concentration of S. feltiae 50 IJs/Female failed to kill any of the engorged females at all of exposure periods. When ticks were treated with high concentrations of H. bacteriophora, the optimum engorged female’s mortality was 100 % after 3 days; nevertheless, when exposed to low concentration of this nematode, more than 70 % of females died within the same duration. These findings are consistent with those of (Samish et al., 1999), who discovered that a high mortality index applying low nematode rates indicates a specific tick species' susceptibility to a nematode species. The presence of a tooth on the front tip of the H. bacteriophora IJs, which promotes penetration and infection, may explain the increased vulnerability of Boophilus microplus engorged females. These data were also confirmed by those of (Mauleon et al., 1993), who mentioned that all of the B. microplus individuals survived after being exposed to a suspension of 1,000 S. carpocapsae IJs from nine different strains. Based on these findings, it is believed that B. microplus must release nematode-killing agents in the hemocel that prevent nematode reproduction. Moreover, the methods employed to collect infectious juveniles and the acquisition period, which is closely related to their infectivity in lab experiments, may be responsible for S. carpocapsae's lack of pathogenicity. The present results investigated that the time needed to kill 50 % of engorged females and the lethal concentration of nematodes which killed 50 % and 90 % of the individuals up to the third day of exposure were both lower in H. bacteriophora than that of S. feltiae and all other Heterorhabditis species (Tables 2,3). The results matched with (Vasconcelos et al., 2004) discovered, who observed that when compared to the results for S. glaseri IJs (i.e., 1,250 and 4,160 IJs/Petri dish, respectively), H. bacteriophora IJs' LC₅₀ and LC₉₀ values of 874 and 1,930, respectively, were low. According to earlier research (Singh et al., 2018); a number of EPN species are lethal to engorged females of R. microplus. In semi-field trials, the use of EPNs to soil containing engorged females had excellent results (Alekseev et al., 2006, Monteiro et al., 2020); however, the same result did not occur when applying EPNs to infested cattle (Goolsby et al., 2018). Similar findings were also attained by (EL Roby et al., 2018), who tested eight Egyptian isolates of EPNs in a laboratory (four belonged to the genus Steinernema and four to Heterorhabditis) against engorged females of the hard tick, B. annulatus and adult females of the soft tick Argas persicus. They reported that Heterorhabditis isolates (10 K and A4) at 1000 IJs/ml have high potency which accomplished 100 % mortality three days post-infection against A. persicus, whereas, only one Steinernema isolate (5B) produced an overall mortality rate of 93.33 %. Meanwhile, mortality rates for 10 K and A4 isolates of Heterorhabditis were 93.33 % and 86 %, however, both Steinernema isolates (5B and AT4) caused 86.7 % mortality. It was evident from the present investigation that the two most virulent EPNs, H. indica NEM-23 and H. bacteriophora NEM-26, had a further effect on the biological characteristics of engorged females of H. dromedarii. All of the engorged females exposed to 300 or 600 IJs/Tick H. bacteriophora in the initial experiments of current study were killed within 3 days post-infection, thus only three concentrations of this nematode were evaluated for biological parameters. Longer exposure times and higher rates of the two EPNs appear to strengthen their impacts on the biological parameters of H. dromedarii engorged females analyzed in this study by allowing a larger amount of nematodes to find and enter the host. The biological parameters of the females in the treated and control groups had statistically different means, highlighting the heterogeneity in several groups and establishing that the variations in these measurements were caused by the two tested nematodes (Tables 4,5). With reference to the parameters survival, oviposition, and pre-oviposition periods of groups treated with H. bacteriophora, being shorter than those of H. indica-treated ones, whereas, NEI, EW, and H % parameters were higher in H. indica treatments than those of H. bacteriophora ones, confirming the potency of H. bacteriophora over H. indica. This suggests that the metabolic conversion process or the synthesis of the nutrients required for egg formation within the pre-oviposition stage were unaffected by the EPN infections. Thus, the best control efficacy (61.3 %) was obtained from H. bacteriophora at 150 IJs/Female, and in the same rate of H. indica, efficacy was lower with value of 30.5 % only. Results that were better than those observed in the current study were reported by (Silva et al., 2012, Monteiro et al., 2020), who noted that using a similar concentration (150 IJ/engorged female) of H. bacteriophora HP88 and H. indica LPP1 lead in an almost 90 % efficacy, causing a noticeably decreased in the number and viability of the laying eggs by R. microplus females. One year later, (Monteiro et al., 2021) concluded that the acaricides chlorfenvinphos, amitraz, and deltamethrin as well as the essential oil of Lippia triplinervis were in compatibility with EPNs against R. microplus engorged females with an efficiency recorded over 95 % (except for HP88 + deltamethrin), and it reached 100 % in LPP1 + amitraz treatment. Likewise, the present data are in line with those previously recorded by (Monteiro and Prata, 2015), who mentioned that these two strains outperform the results obtained when utilizing EPNs from the genus Steinernema and are among the most active against R. microplus.

5 Conclusion

The current investigation concluded that a 24-h in vitro exposure was sufficient to allow the EPNs to infect and kill the engorged H. dromedarii females. However, in order to achieve efficient results, considering the high lethality and deficiency of the tick biological parameters, a 48-h in vitro treatment with H. bacteriophora NEM-26 was required. The findings provide a strong basis for prospective biocontrol agents that could be applied to camel tick management. More laboratory studies to evaluate the influence of computability with other bio-agents or acaricides on the action of EPNs against camel tick are required to supply critical information that will help conducting field studies.

Funding

This work was funded by the deanship of graduate studies and scientific research, Taif university.

CRediT authorship contribution statement

Bander Albogami: Conceptualization, Funding acquisition, Data curation, Writing – original draft, Writing – review & editing, Visualization, Investigation, Validation, Formal analysis, Methodology, Supervision, Resources, Project administration, Software.