Dehydration Tolerance Limit Research Articles

Dehydration tolerance in relation to short day length in nonfed Amblyomma maculatum Koch, 1844 ticks (Acari: Ixodidae)

ABSTRACTTicks utilize a variety of strategies to mitigate water loss and enhance their off-host survival. This is the first report of a primarily tropical zone tick, the Gulf Coast tick Amblyomma maculatum, vector of Rickettsia parkeri, to regulate water loss by photoperiodic induction. Under short-day conditions (10 h:14 h L:D), water loss rates are decreased. This has a positive effect on survival by extending the time it takes to reach the dehydration tolerance limit. When cycled between long- and short-day conditions, the water loss rate drops and then returns to a faster rate after re-entering long-day conditions; this can occur quickly (within a day), multiple times, and in more than one life history stage. The decrease in water loss is more pronounced in immatures than adults. The percentage body water content, dehydration tolerance limit and critical equilibrium humidity are independent of photoperiodic changes. We conclude that any nonfed stage is adapted for survival by enhanced water conservation when the day length shortens.

Pathogenicity by Aspergillus flavus from Gulf Coast tick cadavers (Amblyomma maculatum, Acari: Ixodidae) to any life history stage

ABSTRACTA natural aspergillosis in the Gulf Coast tick, Amblyomma maculatum, is reported for the first time. Under high relative humidity (RH) conditions, field-collected adults died and became enveloped in whitish mycelium from hyphae that protruded from their bodies. The fungus was identified as Aspergillus flavus. Laboratory-colonized eggs, larvae, nymphs, and adults displayed disease symptoms, and A. flavus was reisolated from dead individuals, about 10 days after artificial infection by submersion for 2 minutes in a 1.6 × 108 spores/ml + Tween 20 inoculum of the native A. flavus isolates. Treatment-related mortality was 87% larvae, 67% eggs, and between these extremes for nymphs and adults. Increased water loss rate was a pathogenic consequence of A. flavus infection for all stages. We conclude that A. flavus is a natural regulator of A. maculatum populations, and larvae are particularly susceptible because of their low dehydration tolerance limit.

Short day exposure suppresses water loss rate in the lone star tick Amblyomma americanum and blacklegged tick Ixodes scapularis (Acari: Ixodidae)

ABSTRACTWe report that all non-fed stages of the lone star tick Amblyomma americanum and blacklegged tick Ixodes scapularis have reduced water loss by exposure to short days. This reduction in water loss is more pronounced in larvae and nymphs than in adults. Impressive was the rapid response: all non-fed stages could transition quickly, losing water fast (long day), then slow (short day), and back to fast (long day), with only a single day exposure to short or long day conditions. Short days did not improve the tick’s dehydration tolerance limit. Ticks under short days were capable of absorbing water vapour, so their ability to rehydrate by water vapour absorption is not inhibited by change in photoperiod. Our conclusion is that a short-day-induced temporary quiescence helps to regulate water loss that applies to any non-fed stage for overwintering. The shallow nature of this quiescence implies that ticks could easily become active at any time and re-enter quiescence.

Short day-triggered quiescence promotes water conservation in the American dog tick, Dermacentor variabilis.

A short day-long day exposure comparison of water balance characteristics throughout the life history of the American dog tick, Dermacentor variabilis, was conducted to examine how this tick survives winter-associated dryness. Larvae, nymphs, and adults under potential diapause-inducing conditions (short day, 20 °C) have low water loss rates compared to long day exposed ticks. Above the critical equilibrium activity, these nonfed ticks show greater water gain from lower water vapor activities. In contrast to nonfed stages, eggs and blood-engorged stages (fed larva, fed nymph) were enhanced for water conservation independent of short day exposure and did not display reduced water loss rates under short day conditions. This short day-prompted response in nonfed ticks was distinguished from a genetically programmed diapause as noted in other arthropods by: (1) reduction in water loss was temporary and could be reversed quickly by transferring to long day for only a single day, then re-triggered by returning to short day conditions; (2) switch between low and high water loss rates could be induced multiple times and for multiple different stages; and (3) response by ticks was to the photoperiod they were under, not the condition that was experienced by previous fed stages or in the mother in the case of eggs. Furthermore, short day had no impact on altering body water content, dehydration tolerance limit, instar yields, or developmental stadia. We conclude that a short day-triggered quiescence reduces desiccation stress associated with overwintering in nonfed ticks. This effect on water conservation due to short day exposure is more pronounced for subadults and is likely due to their increased sensitivity to water loss as a result of their smaller size, which is critical to prevent dehydration during the dry winter periods.

Water balance of the American dog tick, Dermacentor variabilis, throughout its development with comparative observations between field-collected and laboratory-reared ticks

Water balance characteristic data are compiled and determined for each non-fed instar of the American dog tick, Dermacentor variabilis, vector of tularaemia and spotted fever rickettsia, comparing wild-caught and laboratory-colonized populations, to establish how habitat influences D. variabilis dehydration resistance. In contrast to ticks from the field, laboratory-colonized ticks show a progression in percentage body water content from a low of 59% in the egg to a high of 68% in the adult (all instars from the field population have similar values, averaging 63%) and are less tolerant of water stress (2–6% reduction in dehydration tolerance (DT)). We presume that these are colony artefacts as a product of relaxing selective pressure by rearing under optimal conditions of temperature, relative humidity (RH) and host quality. For field-collected and laboratory-colonized populations, larvae survive down to 75–85% RH [critical equilibrium humidity (CEH)], but nymphs and adults require moist air of 85–93% RH, and eggs do not absorb water vapour. Larvae, but not eggs, experience rapid water loss at 30–35°C [critical transition temperature (CTT)], which is 5°C lower than that of post-larval instars. Larvae succumb to dehydration more readily (lower DT limit, eggs have the highest) and are more prone to water loss by having a high net transpiration rate (NTR) as a result of their minute body size and high activation energies for water loss. Comparison of DT with water loss during development for seven tick species reveals that NTR is a species-specific characteristic and species that lose water quickly or slowly as larvae do so for subsequent developmental instars. The CEH, CTT and DT reveal little with regard to habitat suitability and matching a tick to a particular habitat. Ticks operate at the microhabitat, not habitat, level, indicating that ticks can find suitable refuges in many different geographic areas, which accounts for the overlapping distribution of ticks with different NTRs.

Proliferation of red velvet mite Balaustium sp. nr. putmani (Erythraeidae) in Ohio based on water relations of active instars

ABSTRACT Population bursts, numbering in thousands of individuals, are characteristic of red velvet mites, Balaustium sp. nr. putmani, in the springtime in Central Ohio. We determined water-balance characteristics for each of the mobile instars (larva, deutonymph, adult female; males are seemingly absent from this population) to link dehydration tolerance with heightened activity in the same habitat. This mite loses water rapidly: larva > deutonymph > adult. None of these active instars could absorb water vapor, unlike many terrestrial mites, indicating that this mite must imbibe liquid as free water or from food sources to maintain water balance. As a voracious predator, most of the liquid is probably obtained from feeding. Developmentally, larvae are the most sensitive and vulnerable to water stress because of their high net transpiration rate and low dehydration tolerance limit. Additionally, urnulae glands are only present in the post-larval instars; hence, larvae lack the protective waterproofing secretion that is provided by these glands. Deutonymphs and adults are much more resistant to desiccation, are capable of losing approximately 40% of their water content before succumbing to death, and have reduced water loss rates. We concluded that population bursts of B. sp. nr. putmani might be a response to abundance of plant pests in the landscape. Deutonymphs and adults are modified for water conservation and are correspondingly active for longer periods of time. Larvae survive for a brief time, which minimizes their exposure to desiccating habitats, and use the cooler temperatures experienced early in the season, which suppress their high rate of water loss.

Moisture requirements for activity/survival of the gulf coast tick, Amblyomma maculatum Koch (Acari: Ixodidae), based on a water balance study of all life cycle stages

To provide information pertaining to features fundamental for survival, activity and spread of the Gulf Coast tick Amblyomma maculatum Koch (Acari: Ixodidae), vector of agents of human spotted fever rickettsiosis (boutonneuse fever) and canine hepatozoonosis, we determined water balance characteristics for each life stage, supplementing earlier work on adults, for a more comprehensive evaluation through the life cycle. The water balance profile of A. maculatum follows a consistent developmental pattern where the egg is the major water-conservation stage, the larva emphasizes water gain (water vapor absorption from drier air; low critical equilibrium activity, CEA), the adult emphasizes water retention (low net transpiration rate) and the nymph is transitional. A. maculatum in the various stages shares a similar dehydration tolerance limit, CEA, percentage body water content and inability to drink free water from droplets with other ticks. The low net transpiration rate of A. maculatum is the distinguishing feature, classifying A. maculatum as xerophilic compared to other tick species and their corresponding stages. Of importance, the low net transpiration rate of A. maculatum does not match the humid environment (predicting high net transpiration rate) where this tick is distributed, rather it reflects conditions of the microhabitat and slightly altered behaviors relevant to drying out that permit survival in the larger areas that they occupy. Thus, the view that net transpiration rate is an indicator of habitat preference in terms of moisture requirements needs to be modified. Ticks operate on a smaller scale (i.e., microhabitat), indicating a need for direct field observations.

Dehydration tolerance of the Rocky Mountain wood tick, Dermacentor andersoni stiles (Acari: Ixodidae), matches preference for a dry environment

Peak activity of the medically significant Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae), during hot summer months in the Rocky Mountains and southwestern Canada was evaluated by determining water balance characteristics for each of its developmental stages. This tick is dry-adapted and has a water balance classification as xerophilic based upon interspecific comparison with other ticks and a low net transpiration (water loss) rate as the distinguishing feature. All stages (eggs excepted) rely on water vapor as the primary source of water, as evidenced by critical equilibrium humidity assessments and an inability to drink free water from droplets. A relatively low dehydration tolerance limit and high net transpiration rate is reported for the larva, indicating that it is the most sensitive stage to water stress in the lifecycle. The xerophilic nature of D. andersoni makes it less dependent upon a moisture-rich environment and identifies overhydration, although unstudied, as the primary factor limiting its distribution to the Rocky Mountain area.

Habitat requirements of the seabird tick, Ixodes uriae (Acari: Ixodidae), from the Antarctic Peninsula in relation to water balance characteristics of eggs, nonfed and engorged stages

The seabird tick Ixodes uriae is exposed to extreme environmental conditions during the off-host phase of its life cycle on the Antarctic Peninsula. To investigate how this tick resists desiccation, water requirements of each developmental stage were determined. Features of I. uriae water balance include a high percentage body water content, low dehydration tolerance limit, and a high water loss rate, which are characteristics that classify this tick as hydrophilic. Like other ticks, I. uriae relies on water vapor uptake as an unfed larva and enhanced water retention in the adult, while nymphs are intermediate and exploit both strategies. Stages that do not absorb water vapor, eggs, fed larvae and fed nymphs, rely on water conservation. Other noteworthy features include heat sensitivity that promotes water loss in eggs and unfed larvae, an inability to drink free water from droplets, and behavioral regulation of water loss by formation of clusters. We conclude that I. uriae is adapted for life in a moisture-rich environment, and this requirement is met by clustering in moist, hydrating, microhabitats under rocks and debris that contain moisture levels that are higher than the tick's critical equilibrium activity.

Developmental profiles in tick water balance with a focus on the new Rocky Mountain spotted fever vector, Rhipicephalus sanguineus

Recent reports indicate that the common brown dog tick, or kennel tick, Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae) is a competent vector of Rocky Mountain spotted fever in the U.S.A. This tick is of concern to public health because of its high frequency of contact, as it has a unique ability to thrive within human homes. To assess the moisture requirements necessary for survival, water balance characteristics were determined for each developmental stage, from egg to adult. This is the first time that water relations in ticks have been assessed throughout the complete lifecycle. Notably, R. sanguineus is differentially adapted for life in a dry environment, as characterized by a suppressed water loss rate distinctive for each stage that distinguishes it from other ticks. Analysis of its dehydration tolerance limit and percentage body water content provides no evidence to suggest that the various stages of this tick can function more effectively containing less water, indicating that this species is modified for water conservation, not desiccation hardiness. All stages, eggs excepted, absorb water vapour from the air and can drink free water to replenish water stores. Developmentally, a shift in water balance strategies occurs in the transition from the larva, where the emphasis is on water gain (water vapour absorption from drier air), to the adult, where the emphasis is on water retention (low water loss rate). These results on the xerophilic-nature of R. sanguineus identify overhydration as the primary water stress, indicating that this tick is less dependent upon a moisture-rich habitat for survival, which matches its preference for a dry environment. We suggest that the controlled, host-confined conditions of homes and kennels have played a key role in promoting the ubiquitous distribution of R. sanguineus by creating isolated arid environments that enable this tick to establish within regions that are unfavourable for maintaining water balance.

Evidence of a maternal effect that protects against water stress in larvae of the American dog tick, Dermacentor variabilis (Acari: Ixodidae)

We report that the ability to absorb water vapor from the air in larvae of the American dog tick, Dermacentor variabilis, changes depending upon moisture conditions where the eggs develop. When development occurs at lower relative humidities, resultant larvae can replenish water stores, maintain water balance, and survive at relative humidities as low as 75–85% RH, a range that agrees with previously published values for the critical equilibrium humidity or CEH. In contrast, exposure to high relative humidity conditions during development elevates the CEH to 93–97% RH. These larvae can survive only at relative humidities that are close to saturation, as 93% RH is a dehydrating atmosphere. For these larvae, absorption at 97% RH can be prevented by blocking the mouthparts with wax, indicating that an upward shift has occurred in the moisture threshold where the active mechanism for water vapor absorption operates. Based on transfer experiments between low and high relative humidities, the CEH of larvae is determined by the relative humidity experienced by the mother rather than the moisture conditions encountered by eggs after they are laid. The fact that no changes in body water content, dehydration tolerance limit and water loss rate were observed implies that adjustments to the CEH conferred by the mother have the adaptive significance of enabling larvae to maintain water balance by limiting the range of hydrating atmospheres.

Inability of the lone star tick, Amblyomma Americanum (L.), to resist desiccation and maintain water balance following application of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae (Deuteromycota)

We report that female lone star ticks (Amblyomma americanum) experience a rapid change in water permeability when treated with the entomopathogenic fungus Metarhizium anisopliae. The amount of water loss is nearly double the rate of control ticks not exposed to this fungus. As a result, ticks are prevented from stabilizing body water levels (water gain ≠ water loss) at hydrating atmospheres greater than the critical equilibrium activity (CEA) of 0.85a v-0.93av (a v = % RH/100) and reach their dehydration tolerance limit in less time. Thus, disruption of water balance is a pathogenic consequence of fungus infection. This served as a benchmark for evaluating effects on ticks of frequently encountered soil molds in nature (wild tick isolates), Aspergillus niger, Cladosporium cladosporioides, Penicillium glabrum and Scopulariopsis brevicaulis. In contrast to M. anisopliae treatment, no effect on tick water balance was noted with topical application of C. cladosporioides, but water loss rates of ticks following treatment with S. brevicaulis fell between both extremes. Water loss rates imply that P. glabrum may be a tick pathogen, whereas A. niger is apparently not able to use ticks as a substrate. Enhanced desiccation arising from these common molds shows the importance of local mycoflora as natural regulators of tick populations. Water loss rates also provide a tool to assess the pathogenicity of different fungal strains targeted for application in the biological control of ticks.

Water Balance Components in Adults of Terrestrial Red Mite <I>Balaustium</I> sp. (Acarina: Erythraeidae)

Balaustium spp. mites are noted for their quickness, red color, population bursts, and ubiquity. Water balance characteristics of adults were assessed to determine their primary source of water to gain insight into the biology and physiology of these poorly studied mites. Characteristics of this mite show that it is xeric adapted, featuring a 71% body water content, 39% dehydration tolerance limit, and a modest water loss rate of 2% h−1. This species is unable to absorb water vapor from atmospheric air which is unusual for mites. This is illustrated by net water losses at water vapor activities close to saturation, failure to maintain the uptake after first day passive gains, and no detectable salt accumulation around the base of the mouthparts in scanning electron micrographs. Thus, enhanced water conservation enables this mite to withstand desiccation, and their aggressive predatory life style has apparently not necessitated evolution of an active uptake mechanism for absorption of water vapor for this mite that obtains most of its water from feeding.

Moisture requirements of a soil imperfect fungus, Scopulariopsis brevicaulis Bainier, in relation to its tick host

We report heightened dehydration in ticks, Dermacentor variabilis (Say), parasitized by a ubiquitous fungus common in soil, Scopulariopsis brevicaulis. Ticks harboring this fungus had greatly accelerated net water loss rates (nearly twice as high compared to controls), and were unable to absorb water vapor from hydrating relative humidities. Parasitism did not alter tick water content and dehydration tolerance. Mortality was attributed to water losses that reached the dehydration tolerance limit of the tick. Because of the impact of S. brevicaulis on tick water balance, varying levels of infection of this fungus may alter the water balance profile, thereby restricting ticks to specific environments. Thus, this is the first study to propose that a naturally occurring fungus may influence the distribution of D. variabilis.