Relationships of Salinity, Relative Humidity, Mud Flat Fiddler Crabs, Ants, and Sea Ox-Eye Daisy With Ixodid Distribution and Egg Survival on the South Texas Coastal Plains

Integrative Alternative Tactics for Ixodid Control

Simple Summary

Hard ticks are important for economic and health reasons, and control has mainly relied upon use of synthetic acaricides. Contemporary development of resistance and concerns relating to health and environmental safety have elicited exploration into alternative tactics for hard tick management. Some examples of alternative tactics involve biological control, desiccant dusts, growth regulators, vaccines, cultural methods, and ingested medications.

Abstract

Ixodids (hard ticks), ectoparasitic arthropods that vector the causal agents of many serious diseases of humans, domestic animals, and wildlife, have become increasingly difficult to control because of the development of resistance against commonly applied synthetic chemical-based acaricides. Resistance has prompted searches for alternative, nonconventional control tactics that can be used as part of integrated ixodid management strategies and for mitigating resistance to conventional acaricides. The quest for alternative control tactics has involved research on various techniques, each influenced by many factors, that have achieved different degrees of success. Alternative approaches include cultural practices, ingested and injected medications, biological control, animal- and plant-based substances, growth regulators, and inert desiccant dusts. Research on biological control of ixodids has mainly focused on predators, parasitoid wasps, infective nematodes, and pathogenic bacteria and fungi. Studies on animal-based substances have been relatively limited, but research on botanicals has been extensive, including whole plant, extract, and essential oil effects on ixodid mortality, behavior, and reproduction. The inert dusts kaolin, silica gel, perlite, and diatomaceous earth are lethal to ixodids, and they are impervious to environmental degradation, unlike chemical-based toxins, remaining effective until physically removed.

Biosurveillance and Research Needs Involving Area-Wide Systematic Active Sampling to Enhance Integrated Cattle Fever Tick (Ixodida: Ixodidae) Eradication

The one-host cattle fever tick, Rhipicephalus (Boophilus) annulatus (Say), and southern cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini), are important ectoparasitic pests of cattle, Bos taurus L., mostly for transmitting the causal agents of bovine babesiosis. Bovine babesiosis inflicted substantial cattle production losses in the United States before the vectors were eliminated by 1943, with the exception of a Permanent Quarantine Zone in South Texas, a buffer along the Mexico border where the invasive ixodids remain. As suitable hosts, infested white-tailed deer and nilgai antelope populations disperse R. annulatus and R. microplus, which increases the risk for emergence of bovine babesiosis in the United States. A R. microplus incursion first detected in 2016 on the South Texas coastal plain wildlife corridor involved infestations on cattle, nilgai antelope, white-tailed deer, and vegetation. Efforts at passive sampling of Rhipicephalus (Boophilus) spp. on hosts are concentrated in the Permanent Quarantine Zone. Hence, a knowledge gap exists on the full extent of the recent incursions. Area-wide, systematic, active sampling and supportive research, involving the Permanent Quarantine Zone, Temporary Quarantine Zone, most of the coastal plain, and other parts of Texas outside of the quarantine zones, are needed to bridge the knowledge gap. Herein, we provide research perspectives and rationale to develop and implement systematic active sampling that will provide an increasingly accurate assessment of Rhipicephalus (Boophilus) spp. distribution in Texas. We suggest that this is essential to advance integrated vector-borne animal disease eradication approaches for keeping cattle free of bovine babesiosis.

Questing by Tick Larvae (Acari: Ixodidae): A Review of the Influences That Affect Off-Host Survival

Questing is a host-seeking behavior in which ticks ascend plants, extend their front legs, and wait poised for a chance to attach to a passing host. Hard ticks are ectoparasites of terrestrial vertebrates and because some species vector disease, they are among the most medically important of arthropod pests. All ixodid ticks require blood to survive and reproduce with the number of blood-hosts needed to complete their life cycle varying among species. The vast majority are three-host ticks requiring a different host for each developmental stage: larva, nymph, and adult. A few, including some of the most economically important species, are one-host ticks, that quest only in the larval stage. Questing is a rate-limiting behavior critical to tick survival and disease transmission. For the off-host larval stage, survival is highly dependent on ecological and physiological factors. Yet, off-host larval ecophysiology is often overlooked for the more obvious adult and nymphal tick-host interactions. This review summarizes the literature on ixodid larval questing with emphasis on how specific biotic and abiotic factors affect off-host survival.

Lethal Effects of a Commercial Diatomaceous Earth Dust Product on Amblyomma americanum (Ixodida: Ixodidae) Larvae and Nymphs

With increasing development of resistance to conventional synthetic acaricides in economically and medically important ixodid species, interest in finding alternative control tactics has intensified. Laboratory bioassays were conducted, using the lone star tick, Amblyomma americanum (L.), as a model species, to assess the efficacy of a diatomaceous earth-based product, Deadzone, in comparison with a silica gel-based product, CimeXa. CimeXa is already known to be highly lethal against A. americanum larvae and nymphs. The two dust treatments were 100% effective against larvae and nymphs within 24 h after contact occurred by immersion in dry dusts and after crawling across a surface treated with the dry dusts. Contact by crawling on a dried aqueous film of the dusts, even at a concentration of 10%, was not as effective as exposure to the dusts in dry powder form. As has been demonstrated with CimeXa, it is likely that Deadzone will be capable of providing prophylactic protection of cattle from economically important one-host ixodids, such as the southern cattle fever tick, Rhipicephalus microplus (Canestrini), which vectors the causal agents of babesiosis. Diatomaceous earth can be stored indefinitely, will remain efficacious for as long as sufficient quantities remain on the substrate, it is a natural (organic) substance, and it might be amenable for limited use in environmentally protected habitats.

Rhipicephalus (Boophilus) microplus (Ixodida: Ixodidae) Larvae Collected From Vegetation in the Coastal Wildlife Corridor of Southern Texas and Research Solutions for Integrated Eradication

The potential for reinvasion of the United States by cattle fever ticks, Rhipicephalus (Boophilus) annulatus and Rhipicephalus microplus (Canestrini), which remain established in Mexico, threatens the viability of the domestic livestock industry because these ticks vector the causal agents (Babesia bovis and Babesia bigemina) of bovine babesiosis. The Cattle Fever Tick Eradication Program safeguards the health of the national cattle herd preventing the reemergence of bovine babesiosis by keeping the United States free of cattle fever ticks. Here, the collection of free-living southern cattle tick, R. microplus, larvae by sweeping flannel flags over vegetation in the wildlife corridor of Cameron and Willacy Counties, TX, is reported. Finding R. microplus larvae on vegetation complements reports of infestations in wildlife hosts inhabiting the southern Texas coastal plains. Land uses and environmental conditions have changed since cattle fever ticks were eradicated from the United States by 1943. These changes complicate efforts by the Cattle Fever Tick Eradication Program to keep cattle in the United States free of the cattle fever tick disease vectors. Current scientific research on technologies that could be used for area-wide management of fever tick larvae in south Texas and how this could be applied to integrated eradication efforts are discussed.

Landscape Ecology of Rhipicephalus (Boophilus) microplus (Ixodida: Ixodidae) Outbreaks in the South Texas Coastal Plain Wildlife Corridor Including Man-Made Barriers

Landscape features and the ecology of suitable hosts influence the phenology of invasive tick species. The southern cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini) (Ixodida: Ixodidae), vectors causal agents of babesiosis in cattle and it infests exotic, feral nilgai, Bosephalus tragocamelus Pallas, and indigenous white-tailed deer, Odocoilus virginianus (Zimmerman), on the South Texas coastal plain wildlife corridor. The corridor extends from the Mexico border to cattle ranches extending north from inside Willacy Co. Outbreaks of R. microplus infesting cattle and nondomesticated ungulate hosts since 2014 in the wildlife corridor have focused attention on host infestation management and, by extension, dispersal. However, there is a knowledge gap on the ecology of R. microplus outbreaks in the South Texas coastal plain wildlife corridor. Ixodid distribution on the wildlife corridor is strongly influenced by habitat salinity. Saline habitats, which constitute ≈25% of the wildlife corridor, harbor few ixodids because of occasional salt toxicity from hypersaline wind tides and infrequent storm surges, and from efficient egg predation by mud flat fiddler crabs, Uca rapax (Smith). Rhipicephalus microplus infestations on nilgai were more prevalent in part of the corridor with mixed low salinity and saline areas than in an area that is more extensively saline. The different levels of R. microplus infestation suggest that man-made barriers have created isolated areas where the ecology of R. microplus outbreaks involve infested nilgai. The possible utility of man-made barriers for R. microplus eradication in the lower part of the South Texas coastal plain wildlife corridor is discussed.

Effects of Silica-Based CimeXa and Drione Dusts Against Lone Star Tick (Ixodida: Ixodidae) on Cattle

Ixodid ticks vector pathogens of humans, livestock, and wildlife, and occur in tropical and temperate regions worldwide. We used the lone star tick, Amblyomma americanum (L.) (Ixodida: Ixodidae), as a model for other ixodid species, including the southern cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini) (Ixodida: Ixodidae). We assessed the lethality of CimeXa, an inert silica-based desiccant dust, and Drione, a silica-based desiccant dust with pyrethrin and piperonyl butoxide (PBO), against A. americanum larvae and nymphs on calves. CimeXa was highly lethal to larvae released onto shaved calf skin 72-96 h previously, and moderately toxic to nymphs. It did not affect immature life stages treated after they began feeding because desiccation was offset by ingestion of blood. Being inert, CimeXa can protect cattle from infestation before feeding occurs for a potentially indefinite period of time. Drione killed immatures within 24 h when released on treated skin and when applied to feeding ixodids because of the pyrethrin and PBO (PBO will also reduce resistance to pyrethrin if it develops). When CimeXa was applied to calves with the hair intact, ≈90% and ≈70% of A. americanum larvae and nymphs, respectively, were killed within 24 h and Drione killed 100% of each life stage. Drione also prevented and drastically reduced egg production and hatching. While CimeXa protects against infestation by immatures, Drione will also control ticks that are feeding. When pyrethrin and PBO in Drione eventually degrade, the silica aerogel carrier can continue to protect against infestation indefinitely.

Metastriate Ixodid Life Stages Protected from Predatory Ants in Texas

Multiple predatory ant species, including the red imported fire ant, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), have been reported to attack ixodids (Ixodida: Ixodidae), but evidence has largely been circumstantial. When living lone star tick, Amblyomma americanum (L.) (Acarina: Ixodidae), eggs, and unfed and blood-engorged larvae, nymphs, and adults were deployed on bait transects with hot dog slices and dead house flies, Musca domestica L., in West, Central, and South Texas. The various ixodid life stages were not attacked while ants were strongly recruited to the hot dog and M. domestica baits. Similarly, when the same ixodid life stages and other baits were placed adjacent to colonies of two ant species (red harvester ant, Pogonomyrmex barbatus (Smith) and the red imported fire ant, Solenopsis invicta Buren) the ixodids were not preyed upon while hot dog slices and dead M. domestica were immediately attacked. Some ant species dragged blood-engorged adult ixodids and eggs away from the colony entrance, where they were originally placed, and discarded them. Evidence and mechanisms for allomone-based ant deterrence in the genera Amblyomma, Dermacentor, and Rhipicephalus (metastriate ixodids) are discussed. Protection of ixodids from predatory ants helps to explain why metastriate ixodids remain problematic worldwide despite the presence of predaceous ants.

Efficacy of Novaluron + Pyriproxyfen (Tekko Pro) Insect Growth Regulators Against Amblyomma americanum (Acari: Ixodidae), Rhipicephalus (Boophilus) annulatus, Rhipicephalus (Boophilus) microplus, and Rhipicephalus sanguineus

Ixodids are globally distributed pests that transmit many disease agents. Increasing resistance to conventional acaricides raises the need for alternative tactics. Novaluron and pyriproxyfen are insect growth regulators (IGRs) that have variable potencies against acarines. We conducted in vitro and in vivo experiments to assess novaluron + pyriproxyfen (marketed as Tekko Pro) against four ixodid species. Laboratory assays on the brown dog tick, Rhipicephalus sanguineus (Latreille) (Ixodida: Ixodidae), and the lone star tick, Amblyomma americanum (L.) (Ixodida: Ixodidae), reduced metabolic activity in larvae and nymphs. Concentrations of novaluron + pyriproxyfen dried on filter paper impeded molting of larval R. sanguineus (less effective against nymphs). Molting A. americanum larvae were reduced by >95% using 4 and 8 µg/cm2 eliminated molting; nymphal molting was reduced but not halted even at 16 µg/cm2. On calves, novaluron + pyriproxyfen stopped larval A. americanum metabolic function 1 d post-treatment and larvae did not molt. When larvae were released 30 d after treatment, metabolic activity was reduced by 95% and molting was reduced by 94%. Southern cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini) (Ixodida: Ixodidae), larvae released 1 d after treatment on calves were 99% prevented from reaching adulthood. The treatment did not interfere with larval development when larvae were released 52 d after treatment. The cattle fever tick, Rhipicephalus (Boophilus) annulatus (Say) (Ixodida: Ixodidae), failed to reach adulthood when larvae were released on calves a day after treatment (residual activity was not assessed for R. annulatus). These IGRs, and possibly others, offer an alternative to conventional acaricides for ixodid control on cattle.