Three beneficial nematodes for Rhipicephalus (Boophilus) microplus control
What are ticks, Rhipicephalus microplus?
Tick,Rhipicephalus (Boophilus) microplus is one of the most important bloodsucking ecto-parasitic pests of both domestic and wild animals including cattle, deer, donkeys, horses, goats, pigs and sheep. Cattle are generally considered as major hosts for this tick and therefore they are named as cattle ticks. These ticks also called as blue ticks, hard ticks or southern cattle ticks. Ticks have four pairs of legs and are related spiders. Unlike other tick species, Rhipicephalus microplus require only one host to complete its life cycle. The life cycle of this tick consists of egg, larva, nymph and adult stages. Of these stages, larvae, nymphs and adults are parasitic to host animals. The life cycle of this tick begins when engorged females drop off the host on the ground and lay eggs on the soil surface under thatch/litter. The eggs hatch into small larvae that climb up grass stems and gather at the tip of leaves where they wait until they get chance to hop on passing by host animals. Once they attach to host, they crawl to their feeding site where they start feeding on host blood. While feeding on the host blood, tick larvae successively molt into nymphs and then into adults. Under optimal environmental conditions, this process of feeding and successive molting on the host’s body takes generally about 20 -25 days to develop into engorged females. The engorged females then drop off the host on the ground where they lay eggs and die, then eggs hatch into larvae and life cycle continues. Based on the optimal environmental conditions, Rhipicephalus microplus ticks can complete 5 generations within a year.
Damages caused by Rhipicephalus microplus ticks to animals:
Direct feeding by parasitic stages such as larvae, nymphs and adults of tick, Rhipicephalus microplus can cause anaemia, hides, irritation, stress, weakness, decreased production and even death in tick infested animals. In addition, Rhipicephalus microplus ticks are vectors of some protozoa parasites including Babesia bigemina and Babesia bovis that are responsible in causing a disease in cows called “cattle fever”.
Biological Control of Rhipicephalus microplus ticks:
As Rhipicephalus microplus ticks themselves and diseases transmitted by them can cause a significant economic loss to cattle and dairy industry, their management is essential. Chemical acaricides may have been effective in controlling ticks but their use is restricted due to their detrimental effects on the animal health and environment. Natural predators including birds, insects (ants and wasps), rodents may be helpful to suppress the populations of ticks but they cannot eliminate entire populations of tick, Rhipicephalus microplus. Other natural organisms including beneficial entomopathogenic fungi and nematodes have a potential to use as environmentally safe biological control agent to control tick, Rhipicephalus microplus.
Effects of beneficial entomopathogenic fungi on Rhipicephalus microplus ticks:
Beneficial entomopathogenic fungi including Beauveria bassiana and Metarhizium anisopliae can be use as biological control agents for controlling ticks. According to Paião et al (2001) beneficial entomopathogenic fungi called Beauveria bassiana can cause up to 70 and 100% mortality of larvae and engorged females of Rhipicephalus microplus ticks, respectively. Similarly, another beneficial entomopathogenic fungi, Metarhizium anisopliae can cause 100% mortality of engorged tick females (Frazzon et al., 2000; Leemon et al., 2008).
Effects of beneficial entomopathogenic nematodes on Rhipicephalus microplus ticks:
Currently beneficial entomopathogenic nematodes from two genera, Steinernema and Heterorhabditis have been successfully used as biological control agents to control many soil-dwelling stages of insect pests of many crops and animals (Grewal et al., 2005). Infective juveniles of these nematodes always carry species-specific symbiotic bacteria in their guts and use as weapon to kill their hosts. Generally, these nematodes enter into host’s body cavity through natural openings and then release their symbiotic bacteria in the blood. These released bacteria then multiply in blood, cause septicemia and kill their host usually within 48 h after infection. Three beneficial entomopathogenic nematodes including Heterorhabditis bacteriophora, Heterorhabditis indica, Steinernema glaseri have showed a potential to use as biological control agents to control tick, Rhipicephalus microplus.
Beneficial entomopathogenic nematode, Heterorhabditis bacteriophora:
The infective juveniles of Heterorhabditis bacteriophora generally move actively throughout the soil profile to seek both mobile and immobile hosts. This behaviour of searching hosts is called “cruise foraging” strategy. Infective juveniles of Heterorhabditis bacteriophora nematodes always carry symbiotic bacteria, Photorhabdus luminescens in their guts and use as weapon to kill their hosts. Generally, these nematodes enter into host’s body cavity through natural openings and then release their symbiotic bacteria in the blood. These released bacteria then multiply in blood, cause septicemia and kill their host usually within 48 h after infection. Since Heterorhabditis bacteriophora nematodes have ability to move throughout the soil profile and even through thick thatch to find their hosts, they can be very good candidates to find and kill engorged females that are already dropped off the hosts on the ground and hiding under thatch for egg laying. Beneficial H. bacteriophora nematodes were also effective in reducing weight of egg masses, egg laying and killing of engorged females of ticks ( Monteiro et al., 2012; Vasconcelos et al, 2004).
Beneficial entomopathogenic nematode, Heterorhabditis indica:
Heterorhabditis indica nematodes are globally distribution and have been considered as the important candidates for the biological control of the fungus gnats, root weevils, white grubs and ticks. Heterorhabditis indica is a heat tolerant nematode and works better against many insect pests when temperature is above 25oC. Recently, da Silva et al (2012) have demonstrated that the reproduction potential of engorged tick females was affected when they were infected with entomopathogenic nematode, Heterorhabditis indica.
Beneficial entomopathogenic nematode, Steinernema glaseri:
Steinernema glaseri is a large size, highly mobile and cruise forager nematode. In addition, these nematodes are specialized in attacking less mobile hosts within the soil profile and therefore, they can be effective against engorged females of Rhipicephalus (Boophilus) microplus tick. It has been demonstrated that the entomopathogenic nematode, Steinernema glaseri can infect engorged Rhipicephalus (Boophilus) microplus female ticks within two hours of exposure and can cause over 90% mortality of ticks when they remain in contact with the ticks for 24 hours (Reis-Menini et al., 2008). In another study, Steinernema glaseri treatment also caused 90% reduction in egg laid by engorged Boophilus microplus females and mortality of females was increased as the concentration of nematode was increased (Vasconcelos et al, 2004).
Combined effects of beneficial entomopathogenic fungi and nematodes:
The combined effects of two beneficial entomopathogenic fungi including Beauveria bassiana and Metarhizium anisopliae and two beneficial entomopathogenic nematodes including Heterorhabditis bacteriophora, Heterorhabditis indica were studied on the weights of egg masses, percentages of egg hatching and mortality of engorged females of Rhipicephalus (Boophilus) microplus tick (Monteiro et al,. 2013). Results of this study showed that both the beneficial entomopathogenic fungi and nematodes whether applied alone or in combination, they were effective in reducing weight of egg masses and percentage of hatching of eggs of treated engorged tick females as compared to untreated engorged tick females. However, the combined effect of an entomopathogenic nematode, Heterorhabditis bacteriophora and an entomopathogenic fungi, Metarhizium anisopliae against engorged Rhipicephalus (Boophilus) microplus female ticks was significantly greater (cause over 90% control) than any other combinations (Monteiro et al,. 2013).
Commercial availability biological control agents:
Currently, only beneficial entomopathogenic nematodes including Heterorhabditis bacteriophora, and Heterorhabditis indica are commercially available.
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