While investigating how forests responded to defoliation stress, Institute ecologists discovered that white-footed mouse populations played a large role in regulating the moths. Key predators on gypsy moth pupae, research showed that moth populations declined when mice were abundant.
More interestingly, scientists discovered a connection among acorn production, mouse population size and the number of blacklegged ticks infected with Borrelia burgdorferi, the bacterium that causes Lyme disease.
Lyme disease is caused by a spirochete bacterium, Borrelia burgdorferi. This bacterium is transmitted to humans during blood meals taken by infected ixodid ticks on human hosts. Several ixodid tick species can transmit the disease; in eastern and central North America the primary vector is the blacklegged tick, Ixodes scapularis.
Larval ticks hatch uninfected and are not initially dangerous to humans. If they feed on an infected host during their larval blood meal, they can become infected and later transmit Lyme bacteria to people. Whether a larval tick will acquire an infection and thus molt into an infected nymph depends largely on the species of host on which it feeds.
Different species of tick hosts tend to have different probabilities of transmitting an infection to a feeding tick. In eastern and central North America, the host most likely to transmit an infection to a feeding tick is the white-footed mouse (Peromyscus leucopus), which infects between 40% and 90% of feeding larvae. Eastern chipmunks (Tamias striatus) and shrews (Blarina brevicauda and Sorex spp.) tend to be moderately competent reservoirs for B. burgdorferi. Most other mammalian, avian, and reptilian hosts have a considerably lower reservoir competence.
Lyme Disease Prevalence & Mice
White-footed mice are the principal natural reservoirs for Lyme disease bacteria. Ticks that feed on mice are highly likely to become infected, making them capable of transmitting Lyme disease to people during their next blood meal. When they feed on mice during their larval and nymphal stages, ticks are more likely to survive and molt. Ticks that feed other vertebrate host species have a comparatively lower survivorship. Consequently, we have hypothesized that the greater the abundance of mice during the midsummer peak in larval tick feeding activity, the greater the probability that questing larval ticks will encounter a mouse, and the higher the probability that they will molt into an infected nymph capable of transmitting Lyme bacteria one year later.
Our long-term monitoring of mouse abundance, tick abundance and infection prevalence in southeastern New York State supports these hypotheses. In addition, because we have demonstrated a correlation between acorn production and mouse abundance the following year, we have hypothesized that acorn abundance is a good predictor of abundance and infections prevalence of ticks almost two years in advance. This hypothesis also is supported by our monitoring data.