A recent paper in Science [Jones et al., 1998, 279(13):1023-1026] presents strong evidence that mast production in eastern United States oak forests is directly linked to levels of gypsy moth outbreaks and Lyme disease. The paper describes how researchers set up experiments that could control the levels of acorns and mice on experimental plots. The results indicated that acorn levels determine the population levels of white-footed mice and white-tailed deer in oak forests. Results also indicated that mice eat gypsy moth pupae and can thereby control the severity of gypsy moth outbreak. For example, the researchers found about 45 times more pupae and moth egg masses in plots with fewer mice.
Mice are carriers of the Lyme disease spirochete, and mice in acorn-rich plots did have 40 percent more tick larvae than mice in other plots. As of yet, no direct measurements have been made to verify that more infected juvenile ticks exist on the high-acorn plots the following summer. However, it is likely that mast production can be used as a leading indicator for Lyme disease risk.