LB 4-19 - Victory for the vectors? Climatic stress decreases tick survival but increases host-seeking behavior

Thursday, August 18, 2022

5:00 PM – 6:30 PM EDT

Located in: ESA Exhibit Hall

Presenting Author(s)

Caleb Nielebeck

Pepperdine University, United States

Coauthor(s)

SK

Sang Hyo Kim

Pepperdine University, United States
AP

Antonio Pepe

Farmingdale State College, United States
LH

Lucian Himes

Pepperdine University, United States
ZM

Zachary Miller

Pepperdine University, United States
SZ

Sophia Zummo

Pepperdine University, United States
MT

Mary Tang

Pepperdine University, United States
JM

Javier Monzon, PhD

Pepperdine University, United States

Background/Question/Methods:

Ticks are vectors of many diseases including anaplasmosis and Lyme disease, and they are expanding in geographic distribution. However, how ticks will fare in rapidly changing environments due to climate change remains unclear. Therefore, we used a novel method to simulate climatic stress on individual ticks of three species - Amblyomma americanum, Dermacentor variabilis, and Ixodes scapularis - to evaluate their survival, physiology, and behavior. We hypothesized that climatic stress reduces the survivorship of ticks and increases the frequency of tick host-seeking behavior, or questing, because they require water and nutrients from the blood of a host to survive. We placed 144 adult ticks of each species in two temperature ranges (15-25°C and 25-35°C) and three relative humidity (RH) treatments (32%, 58%, and 84%). We assessed the ticks daily for survivorship and questing, which is when a tick is perched with its front legs outstretched to latch on to a host. We measured water loss by comparing the mass of each tick when it died to when it was fully hydrated. In a second experiment, we placed 18 ticks of each species at 35°C and 32% RH. We assessed the ticks every three hours for survivorship, questing, and water loss.

Results/Conclusions:

In the first experiment, generally ticks at the higher temperature range and lower humidities died faster than ticks at the lower temperature range and higher humidities. Ticks of all three species consistently died after losing approximately 30% of body mass due to water loss, but Ixodes reached that threshold much faster than the other two species. Ticks of all three species were more likely to quest shortly before their death. In the second experiment, the rate of water loss was linear for all three species and, again, ticks were more likely to quest shortly before their death. With frequent checks, we were able to more accurately measure the approximate weight loss at which each tick died. On average, Dermacentor died at 27.8%, Amblyomma at 27.5%, and Ixodes at 29.7%. However, Ixodes lost water at a rate of 2.5% of their body mass per hour, 6.25× faster than Amblyomma and 12.5× faster than Dermacentor. These results demonstrate that climatic stress increases tick mortality but also increases tick questing. Further investigations of ticks’ behavioral and physiological responses to abiotic stress are necessary to develop robust models of how climate change will affect transmission of tick-borne diseases.