Unit 2: Introduced Insect Herbivores in Eastern Deciduous Forests. Video 3.

Introduced Insect Herbivores in Eastern Deciduous Forests

Examples of Introduced Insect Herbivores

  • Asian Lady Beetle:
    • There are about nine species of lady beetles in the northeast United States, and three are invasive.
    • Identified by a W shape on their head capsules.
    • Variability in spots and colors within the species.
  • Japanese Beetle:
    • The maggot is the immature form of the Japanese beetle.
    • A common pest that consumes a wide variety of plants in gardens and forests.

Disparity in Invasion Success

  • European insects are 100 times more likely to successfully invade North America compared to North American insects invading Europe.
  • Question: Why are European insects significantly more successful at invading North America than vice versa?

Categories of Consideration

1. Number of Invaders
  • Hypothesis: The number of invaders is proportional to the size of the passage, suggesting more opportunities from Europe to North America.
  • Counterargument: Travel between Europe and North America is roughly the same, making this factor unlikely to be a major contributor.
2. Number of Species Available
  • Hypothesis: A larger number of European species could lead to more successful invasions.
  • Reality: Species richness is similar between Europe and North America.
    • Species richness is the number of different species represented in an ecological community, landscape, or region.
3. Ecological Opportunities
  • Host plants in North America are closely related to those in Europe (similar taxa chemically and morphologically).
  • Native plants share similarities in abundance, morphology, ecology, and phenology.
    • Phenology: The timing of events in plants throughout the year (e.g., leaf growth, flowering, dormancy).
  • North America has two times more tree species due to less extinction during the last glacial period.
  • Less fragmented habitats and less disturbance in North America.
  • Larger diversity of tree species allows for quicker diversification of invasive insects.
  • Large number of European invasive plants already present in North America.
    • Many were intentionally introduced for gardens, providing familiar food sources for European insects.
4. Invader Superiority
  • European organisms have faced severe impacts since the appearance of the Alps.
  • East-west orientation of the Alps resulted in glaciers scouring habitats, leaving minimal refuge.
  • North-south orientation of mountain ranges in the United States provided more refuge during glacial periods.
  • Dryness in southern Europe and 10,000 years of agricultural disruption have led to harsher conditions.
  • Constant landscape modification in Europe has resulted in tougher habitats compared to relatively stable North American habitats.
  • Selection for traits that increase survivability in patchy, fragmented, impoverished, and dry habitats.
Traits Exhibited by European Insects
  • Plasticity: The ability to change physical or behavioral traits based on environmental conditions.
  • Greater percentage of uniparental reproduction (parthenogenesis):
    • 40%40\% of introduced insects can reproduce parthenogenetically, compared to 11%11\% of native insects.
  • More eggs laid, leading to more stable populations.
  • Increased autapomorphy:
    • Ability to have cells function with a single copy of genetic information.
    • Ability to replicate genetics without a mate.
    • Tolerance to higher levels of genetic information (three, four, five, or six times the traditional amount).
  • More significant dispersal:
    • Farther distances and with greater assuredness compared to North American insects.
  • Better ability to deal with competitors, predators, and parasites:
    • Evolved defense mechanisms due to stressful conditions.
  • Ability to withstand harsher conditions for longer periods of time:
    • Increased stress tolerance and successful diapause (dormant period).

Level of Responsibility for Success

  • Opportunities to move: Low.
  • Number of species available: Low.
  • Greater ecological opportunities: Significant.
  • Superior competitive and behavioral abilities: Significant.

Concerns

  • Invasive insects like spongy moth caterpillars, Japanese beetles, and Asian lady beetles are causing significant disruption to ecosystems.
    • They dramatically disrupt ecosystems by affecting food webs and consumption patterns.

Course of Action

  • Difficult to control due to rapid population growth and success.
  • Local insecticides can reduce populations in yards and gardens.
  • Controlling them in forests, old fields, or marshes is nearly impossible once established.
  • The focus of the next lecture will be ecological concepts, followed by a discussion on population dynamics in the eastern deciduous forest.