A novel laboratory method to simulate climatic stress with successful application to experiments with medically relevant ticks

Abstract

Ticks are the most important vectors of zoonotic disease-causing pathogens in North America and Europe. Many tick species are expanding their geographic range. Although correlational evidence suggests that climate change is driving the range expansion of ticks, experimental evidence is necessary to develop a mechanistic understanding of ticks’ response to a range of climatic conditions. Previous experiments used simulated microclimates, but these protocols require hazardous salts or expensive laboratory equipment to manipulate humidity. We developed a novel, safe, stable, convenient, and economical method to isolate individual ticks and manipulate their microclimates. The protocol involves placing individual ticks in plastic tubes, and placing six tubes along with a commercial two-way humidity control pack in an airtight container. We successfully used this method to investigate how humidity affects survival and host-seeking (questing) behavior of three tick species: the lone star tick (Amblyomma americanum), American dog tick (Dermacentor variabilis), and black-legged tick (Ixodes scapularis). We placed 72 adult females of each species individually into plastic tubes and separated them into three experimental relative humidity (RH) treatments representing distinct climates: 32% RH, 58% RH, and 84% RH. We assessed the survival and questing behavior of each tick for 30 days. In all three species, survivorship significantly declined in drier conditions. Questing height was negatively associated with RH in Amblyomma, positively associated with RH in Dermacentor, and not associated with RH in Ixodes. The frequency of questing behavior increased significantly with drier conditions for Dermacentor but not for Amblyomma or Ixodes. This report demonstrates an effective method for assessing the viability and host-seeking behavior of tick vectors of zoonotic diseases under different climatic conditions.

Climatic stress decreases tick survival but increases rate of host‐seeking behavior

“…The experimental conditions of the present study did not affect questing height, except for D. variabilis , which quested at significantly higher heights in warm, humid conditions. This is consistent with our previous study in which we observed that questing height was positively associated with RH in D. variabilis (Nielebeck et al, 2022). Since questing height affects the likelihood of contacting humans (Arsnoe et al, 2015), these results indicate that climate change may impact the risk of tick‐borne disease transmission differently depending on the behavioral and physiological ecology of the vector.…”

“…A. americanum and I. scapularis ticks quested more frequently at the warmer experimental temperature. In a previous study, we observed that the proportion of D. variabilis ticks questing increased with drier conditions (Nielebeck et al, 2022). The experimental conditions of the present study did not affect questing height, except for D. variabilis , which quested at significantly higher heights in warm, humid conditions.…”

“…We hypothesized that climatic stress reduces tick survivorship but enhances the rate of tick host‐seeking behavior, especially as ticks experience increasingly life‐threatening levels of water loss. Our previous research showed that, in climatically stressful conditions, survivorship of I. scapularis is much lower compared to A. americanum or D. variabilis (Kim et al, 2022; Nielebeck et al, 2022). In this study, we tested the hypothesis that I. scapularis ticks have a lower DT or a higher NTR, thus accounting for their lower survivorship.…”