Dutchess County Research Site Tracks 35 Years of Ticks
“On balance, these surprises have enriched our knowledge of this system, helping us to inform management of tick-borne disease risk,” said Richard Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies.
Nearly 500,000 Americans receive a Lyme disease diagnosis each year, making the infection caused by the bacterium Borrelia burgdorferi the most frequently reported tick-borne illness in the United States. For more than 35 years, researchers at the Cary Institute in Millbrook, New York, have tracked the relationships among mice, ticks, oak trees, weather, and predators.
White-Tailed Deer Population Shows No Link to Nymph Abundance
When Lyme disease gained recognition during the 1980s, white-tailed deer were considered a likely driver of rising tick populations because hunters frequently found adult ticks on them. Scientists reasoned that larger deer populations would allow more female ticks to reproduce and increase the number of young ticks capable of spreading infections.
Monitoring on the institute’s 2,000-acre forested property in Dutchess County found no statistically significant connection between deer numbers and the abundance of nymphal ticks. “We had detected a weak positive relationship between deer and subsequent nymph abundance over short subsets of the data, but the whole data set in its entirety shows no such thing,” said Ostfeld.
White-Footed Mice Predict Tick Surges
While deer populations failed to predict nymphal tick numbers, mouse populations showed a much clearer relationship in the long-term data. Years with especially large mouse populations were followed by approximately 40% more nymphal ticks the next year, according to the findings.
White-footed mice serve as effective blood meal providers for tick larvae and transmit Borrelia burgdorferi efficiently. Once infected as larvae, ticks retain the bacteria as they develop into nymphs capable of passing the infection to humans.
Acorn Crops Forecast Ticks Two Years Ahead
Oak trees periodically produce exceptionally large crops of acorns in synchronized events known as acorn masting. These productive years provide abundant food for forest rodents, allowing mouse populations to expand during the following year.
That mouse increase then supports larger numbers of young ticks, meaning a heavy acorn crop reliably predicts an increase in nymphal ticks two years later. This sequence offers researchers a tool for anticipating periods of greater Lyme disease exposure.
Forest Animal Diversity Controls Infection Rates
Mouse abundance predicts how many nymphal ticks appear, but it does not consistently predict what percentage of those ticks will carry Lyme disease bacteria. Skunks, squirrels, and opossums also host feeding ticks, but most are less effective at passing the bacterium.
“So the infection prevalence in the nymphs really depends on how all the larval tick meals are distributed across all the hosts,” said Ostfeld. “It would have been convenient if one host predicted that for us, but that has not been the case.”
Ticks Survive Extreme Temperatures by Retreating into Soil
Laboratory experiments suggested that intense heat or severe cold could kill blacklegged ticks, but observations in natural habitats revealed that ticks are surprisingly capable of surviving these conditions. Researchers believe ticks protect themselves by retreating into deeper soil layers or beneath fallen leaves. Warmer years overall tended to be followed by fewer nymphal ticks than usual.
The research site has undergone significant environmental changes since monitoring began in 1991, including climate shifts, landscape alterations, and the arrival of invasive species. “We need to know what to expect from the different manifestations of climate change, which are sometimes warmer and drier, and sometimes warmer and wetter,” said Ostfeld.
Frequently Asked Questions About Lyme Disease Ecology
How do blacklegged ticks survive extreme cold in the wild?
Ticks protect themselves from temperature extremes by retreating into deeper soil layers or hiding beneath fallen leaves where conditions are less severe than at the surface.
Why are white-footed mice so important for Lyme disease transmission?
White-footed mice provide excellent blood meals for tick larvae and are highly effective at transmitting the bacterium Borrelia burgdorferi to the ticks feeding on them.
What role do animals like opossums and skunks play in tick-borne illness?
Opossums and skunks serve as hosts for feeding ticks, but they are much less effective at passing the Lyme disease bacterium to them than mice are.
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