Blake W. Nelson

Water balance attributes for off-host survival in larvae of the winter tick (Dermacentor albipictus; Acari: Ixodidae) from wild moose

ABSTRACT To explore how the one-host tick Dermacentor albipictus survives off-host, we determined water balance characteristics of eggs and larvae. In contrast to eggs, larvae lost water fast, absorbed water vapour and died from a low amount of water loss. Placing mated females under near water-saturated conditions yielded larvae that absorbed and survived only at high relative humidities. We observed larvae forming clusters. Water loss rate of larvae decreased as group size increased. In response to day length, larvae lost water slower under long day than short day conditions. Larvae could switch quickly between fast water loss rate (short day) and slow water loss rate (long day) within a day, independent of the photoperiodic experience of the egg or mother. Long day exposure had no effect on water relations, incubation and survival of eggs. We conclude that eggs are modified for water conservation. Larvae survive by having a water balance maternal effect; i.e. capacity for water vapour absorption in the larva is determined by the relative humidity experienced by the mother. Larvae regulate water loss behaviourally through larval clustering and summer quiescence. Understanding these water balance attributes and effects of desiccation on egg and larval survival during summer are important to better predict the potential population impacts of winter ticks on moose.

Behavioral correction to prevent overhydration and increase survival by larvae of the net-spinning caddisflies in relation to water flow

We report behavioral regulation of body water content in caddisfly larvae, Hydropsyche morosa and Cheumatopsyche pettiti, by selecting microhabitats with different water flow rates. The purpose of our study was to examine features necessary for survival in the same apparent habitat, because the two species co-exist in riffle areas of freshwater streams. Both species are highly sensitive to water loss as a result of high water loss rates and depend on immersion in fresh water (hypo-osmotic) to maintain water stores. In contrast to C. pettiti, H. morosa is larger, retains water more effectively, and features reduced water loss rates with suppressed activation energies. When H. morosa was confined to areas of low or no water flow, overhydration led to rapid mortality, whereas the same conditions favored water balance maintenance and survival in C. pettiti. In attraction bioassays, H. morosa moved and remained within areas of high water flow and C. pettiti preferred areas with low water flow. Because water flow rates are unlikely to directly impact water gain, the mechanism responsible for increased survival and water balance maintenance is likely related to the impact of water flow on oxygen availability, differences in feeding ecology, or other underlying factors.

Larval behaviour of the winter tick, Dermacentor albipictus (Acari:Ixodidae): evaluation of CO2 (dry ice), and short- and long-range attractants by bioassay

ABSTRACT We report that larvae of Dermacentor albipictus can detect CO2 from a dry ice source at distances up to 3.0 m and initiate increased activation, movement and questing behaviour. The maximum distance that larvae spread was ~0.5 m after 24 h, compared to <0.1 m without CO2 as an excitant. In Petri dish bioassays, 2,6-dichlorophenol, methyl salicylate and o-nitrophenol acted as attractants, albeit with mixed results at 1.0 m, 2.0 m and 3.0 m, respectively. The 2,6-dichlorophenol target was the most effective, although few larvae crawled >1.0 m and CO2 was required as a carrier. In Petri dish bioassays, larvae arrested into dense aggregations on eggshells collected after hatching. This arrestment was associated with the eggshell lipids cholesteryl oleate and cholesteryl palmitate, implying that cholesteryl esters act as assembly pheromones for larvae. Faster response was evident at 65% relative humidity (RH) versus 95% RH. Larvae were not arrested by tick excreta, guanine or related purines. Although larvae can be activated from long distances, in the field they remain fairly localized around the egg mass (hatching location), have limited dispersal and are more responsive in drier conditions. Given their arrestant properties, cholesteryl oleate and cholesteryl palmitate may prove useful in pheromone-assisted control methods because D. albipictus larvae are the single stage of infestation to the host.

Knot formation reduces water exchange by adult males of the hairworm, Paragordius varius (Nematomorpha: Gordioidea)

To examine how aggregation by hairworms may enhance survival in freshwater, we determined water balance characteristics of Paragordius varius in groups of different sizes. P. varius is hyperosmotic resulting in high body water content and functions down to one-half of water stores. Absence of a critical transition temperature implies a watertight, low-porosity cuticle. Aggregated worms lose water slowly, as a physiological consequence of reduced motor activity. The water balance strategy shifts from a reliance on high dehydration tolerance for isolated individuals, affording high water loss rates, to suppressed activation energy when aggregated, wherein blocking water gain is important when water loss is slower. Low water loss rate derives from stillness and aggregating that facilitate mating or anti-predator defense, rather than as a behavior to regulate water loss. Presence of hairworms in streams is an indicator of high-quality water that is necessary to maintain water balance.

Engorged nymphs act as a conditioning stage to protect adult American dog ticks and lone star ticks (Acari: Ixodidae) against heat stress

To correlate proper development and survival with moulting in hot summers for adults of the American dog tick Dermacentor variabilis and the lone star tick Amblyomma americanum, the maximum heat shock response was determined for engorged nymphs. An impressive ability to moult successfully with near complete adult survival occurred with 1-hour heat shock as high as 46°C for both species. Heat shock exposures at and above 48°C were detrimental, disrupting regular life history pattern by extending the crawling phase and severely reducing the number of adults that emerged. Amblyomma americanum was characterized by completion of adult development from engorged nymphs, greater adult yield, and enhanced adult survival in response to short-term heat exposure up to 50°C for engorged nymphs and 54°C for adult females. Both species featured the improved ability to recover from heat-induced injury as adults following prior exposure to heat at an ecologically relevant temperature (32ºC) as an engorged nymph. Capacity for recovery from heat-related injury was particularly heightened for A. americanum. We conclude that A. americanum is more heat tolerant than D. variabilis, engorged nymphs are a conditioning stage for acclimating adults to high temperature, and negative effects of heat stress on fed nymphs is unlikely to prevent, but may delay, adult development at the temperatures that occur naturally.

Fungi and the Effects of Fungicides on the Honey Bee Colony

Fungicides are found in agricultural areas to protect crops from fungal diseases. When sprayed in areas where honey bee colonies are placed for pollination, bees can collect or otherwise be exposed to these compounds. While labeled safe for bees by the manufacturers, our research found that pollen containing fungicides had a negative effect on the beneficial fungi found in bee colonies that help converting the pollen into bee bread and can end up in the bees themselves. As a result, pathogenic fungi (that cause chalkbrood and stonebrood diseases) were not kept in check by the beneficial fungi, including Aspergillus, Penicillium, Cladosporium, and Rhizopus, which were compromised by the presence of fungicides in the hive. Colonies were found to be weakened by the persistent presence of fungicides. Steps to help protect colonies are outlined.

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

ABSTRACT Ticks 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.