Yuexun Tian, PhD candidate
Entomology & Nematology Department
Florida Medical Entomology Lab
University of Florida

Supervisor: chair Cynthia Lord PhD, co-advisor Phil Kaufman PhD
Project 3: Ecological and insecticide-resistance models of tick vectors in Florida
Aim 4: Rhipicephalus sanguineus dynamics and impacts of acaricide resistance

Yuexun Tian is a PhD candidate in the Florida Medical Entomology Lab and Entomology and Nematology Department at the University of Florida, advised by Dr. Cynthia Lord and Dr. Phil Kaufman. Yuexun completed her bachelor’s degree at China Agricultural University and gained some research experience that led to her masters work at Auburn University in Alabama studying the toxicity and repellent effects of essential oils on house flies. Growing up in China, ticks were not a common worry for Yuexun, but in her masters work she was often warned about the dangers of ticks and tickborne diseases such as Lyme disease. Yuexun soon reached out to Dr. Kaufman at University Florida, and learned of the position with Dr. Lord and the CDC Southeastern Center of Excellence in Vector Borne Diseases. Yuexun wanted to continue her education and gain awareness about ticks and how to protect people from tick encounters.

(Left to right) Dr. Phil Kaufman, Yuexun Tian, Dr. Cynthia Lord, at Yuexun’s proposal

For her dissertation, Yuexun studies the brown dog tick, Rhipicephalus sanguineus. Unlike other common species of ticks in the southeast (lone star ticks, American dog ticks, etc.) brown dog ticks can infest homes and can be very hard to control. Yuexun recently completed a Featured Creatures article on brown dog ticks that you can read here.

Left: Over 100 flat adult brown dog ticks Right: Blood-fed brown dog tick females laying eggs

Left: Blood-fed brown dog tick larvae Right: Blood-fed brown dog tick nymphs

Yuexun’s research includes experiments and mathematical modeling to better understand the phenology and insecticide resistance of brown dog ticks. To better understand the phenology of this tick, they are using three different tick strains: one that has been in the lab for many generations, and two more recently collected from the field, one in California, and one in Florida. With these three colonies they are able to test a variety of temperature ranges and humidity levels to see how the developmental parameters and survival times vary between them. They also use these strains of ticks to examine resistance in the tick populations. This is done using larval packet tests that identify the concentration of permethrin or fipronil needed to achieve a desired mortality level, such as 50% or 99%, following exposure.

Left: Incubator with fixed temperature and two aquariums with fixed humidity for tick developmental and survival evaluations
Right: Yuexun performing a larval packet test

Working with Dr. Lord and her colleagues, Yuexun has been using the information from her survival and longevity experiments to develop a mathematical model to improve our understanding of how phenology is affected by residential conditions. From the experiments they can learn the time needed by a fed female tick to develop and then lay her eggs, how long it takes before the eggs hatch into larvae, how long it takes fed larvae to molt into nymphs, how long it takes fed nymphs to molt into adults, and other useful parameters. Unlike population based models, they use individual-based models which allows them to monitor each tick over a given environment. By tracking each of the thousands of ticks in the experiment, they can incorporate the dynamics of how brown dog ticks survive in different rooms in a house, or how host (dog) availability can change their survivorship. By better understanding the brown dog tick, they hope to provide insight on protecting humans and other animals from ticks and tick-borne diseases. Below are two diagrams showing how brown dog ticks infest a home and how temperature and humidity vary in different areas of a home.

Early stage of brown dog tick infestation in a home with only adult ticks present

Late stage of brown dog tick infestation with multiple life stages present

Yuexun has presented at several conferences. Most recently, she presented a poster at this year’s Emerging Pathogens Institute Research Day titled “Resistance expression of permethrin and fipronil in multiple Rhipicephalus sanguineus populations”. She also delivered an oral presentation at the Entomological Society of America titled “The changing phenology of residential Rhipicephalus sanguineus infestations.”

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Blood-fed brown dog tick females