Issues : Figure Sets

Figure Set 5: Gypsy Moth Invasion and Links to Outbreaks of Lyme Disease

Purpose: To allow students to piece together the 3-way interaction of gypsy months, mice, and Lyme disease.
Teaching Approach: "jigsaw"
Cognitive Skills: (see Bloom's Taxonomy) — comprehension, interpretation, synthesis
Student Assessment: diagram quiz


This study by Jones et al. (1998) involves an introduced insect, the gypsy moth (Lymantria dispar). The moth was intentionally introduced into Massachusetts for potential silk production in the 1880’s. By 1987 the moth was established throughout the Northeast. It has now spread south to the Virginias and west to Michigan and to numerous other states throughout the U.S. It has become a serious pest on native and ornamental trees in the U.S. In parts of New England, defoliation of oaks in particular has occurred numerous times due to gypsy moth outbreaks.

Since 1980 gypsy moths have defoliated about a million acres of forest a year. In 1981 roughly 13 million acres were defoliated - an area larger than Massachusetts and Connecticut combined. Gypsy moth larvae prefer hard woods but feed on hundreds of tree and shrub species. When populations are dense they eat almost any vegetation. Trees are killed when they have been greatly defoliated (more than 50% of summer foliage) several times, or when stressed by other factors such as drought.

The life cycle of gypsy moths involves 4 stages: eggs larvae, pupae, and adult moths. Only the larvae damage vegetation. The moth lays egg masses on tree trunk, and branches and hatching coincides with leaf budding of hardwoods in the spring. Larval dispersal happens via silken threads on the winds or human transportation of wood and other objects. Larvae molt numerous times; these stages are called instars. In mid-summer larvae enter the pupae stage when they morph into adult moths. Moths mate in mid—late summer; eggs don't hatch until the following spring.

This Issue is based on a Science paper by Jones et al. (1998) that links heavy oak acorn production with degrees of gypsy moths outbreaks and Lyme disease. The data supports the idea that acorn biomass determine populations of white-footed mice and white-tailed deer in oak forests. Since mice eat gypsy moth larvae, they can decrease moth outbreaks.

In addition to eating moth larvae, those mice harbor the Lyme disease bacterium. Lyme disease is very serious in the northeast U.S.; if untreated it leads to severe joint and nervous system problems. Therefore this paper suggests that Lyme disease infection is higher in summers fallowing oak mast years (high acorn productions) and that acorn biomass could be used to predict Lyme disease risk.

The Jones et al. paper is a terrific example of the complex interactions between organisms in an ecosystem — and the surprising effects of these interactions on people.

In this 3-way jigsaw the first set of groups work on Figures 5a, 5b, and 5c, respectively, and they become “experts” on their figure. In the second grouping, students explain the 3 figures to each other and attempt to put the whole acorn-mouse-deer-tick-lyme disease puzzle together.

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