Plant Stress & Insect Pests

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Plant Stress & Diversity with Impacts on Insects

1 Widely held belief that stressed plants are better food for insects and mite pests than healthy plants.

2 Plant stress is one of the mechanisms often cited for pest outbreaks following adverse environmental conditions such as drought or pollution.

Plant Stress Hypothesis

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Plant Stress & Diversity with Impacts on Insects

1. 70 experimental studies of plant stress response were reviewed

2. Stresses included: drought water logging shading pollution

Test of the previous hypothesis

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Plant Stress & Diversity with Impacts on Insects

3. 66 insects spp and 40 plant species were involved.

4. Insects organized into 5 feeding guilds:– chewers– suckers– leaf miners– gall makers– borers

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Plant Stress & Diversity with Impacts on Insects

a. Overall, plant stress had no significant effect on growth rate, survival, or plant density.

b. Variation in insect response did exist and was mostly related to insect guilds.

c. Boring and sucking insects performed better on stressed plants.

d. Gall making and chewing insects were affected adversely by plant stress.

e. Leaf miners were generally unaffected by stress.f. Plant age and growth rate affect outcome of plant stress

on insects.

Results:

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Plant Stress & Diversity with Impacts on Insects

• They can directly affect insect pests.

Elevated temperatures may:* Advance emergence dates of pests

* Inc. the # of generations each growing season

* Allow spp adapted to warm climates to expand there ranges northward

* Unbalance predator-prey interactions in favor of the pest

Environmental factors

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Plant Stress & Diversity with Impacts on Insects

Drought may:

Reduce the infection rates of pests by pathogenic fungi

Reduce survival rates of certain soil dwelling pests such as weevils and white grubs

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Plant Stress & Diversity with Impacts on Insects

1. No natural enemies found in hot stressed areas!

2. These conditions can be found in disturbed landscapes.

3. Restoration can take place by:• Use of trees to increase shade• Addition of natives to restore natural systems• Accumulation of organic matter

The Role of Diversity:

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Plant Stress & Diversity with Impacts on Insects

Lack of Diversity

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Plant Stress & Diversity with Impacts on Insects

Lack of Diversity

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Plant Stress & Diversity with Impacts on Insects

Lack of Diversity- It’s Everywhere

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Plant Stress & Diversity with Impacts on Insects

Every Neighborhood!

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Plant Stress & Diversity with Impacts on Insects

More Problems

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Plant Stress & Diversity with Impacts on Insects

What We Need to be Striving For:

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Plant Stress & Diversity with Impacts on Insects

Diversity Mean “Binding” Things Together

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Plant Stress & Diversity with Impacts on Insects

Turf & Tree Roots Don’t Co-exist

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Plant Stress & Diversity with Impacts on Insects

Therefore: Create Zones of Plantings

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Plant Stress & Diversity with Impacts on Insects

• Diverse systems bring in more different kinds of pests but…. Less numbers of each pest!

• Diverse systems have more predators in the landscape.

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Plant Stress & Diversity with Impacts on Insects

Diverse Systems

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Plant Stress & Diversity with Impacts on Insects

• Therefore, diverse landscapes with many potential pests provide many food sources for these predators.

Predators Are Generalists

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Plant Stress & Diversity with Impacts on Insects

Diversity can be Geographical

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Plant Stress & Diversity with Impacts on Insects

1. Lack stability and sensitive to destruction.

2. They have peaks and valleys of pests.

e.g. Pest arrives, predators come in, predator population drops due to a lack of food source, then the pest resurges.

Monocultures

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Plant Stress & Diversity with Impacts on Insects

Trees vs. Turf

They are mutually exclusive in nature.

Trees are not found in the mid-west prairies.

Grasses are not found growing on forest floors.

There is competition between the two plant types.

Unbalanced Landscapes

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Plant Stress & Diversity with Impacts on Insects

Trees vs. Turf

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Plant Stress & Diversity with Impacts on Insects

• Impossible to separate fertilizer applications in this system.

• Turf takes up the majority of fertilizer but, trees near turf can still receive enough fertilizer to trigger over-abundant growth and a reduction in defense and storage capabilities.

Fertilizer Interactions

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Plant Stress & Diversity with Impacts on Insects

• Over fertilized trees are pre-disposed to other problems such as insect attack.

Fertilizer Interactions

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Plant Stress & Diversity with Impacts on Insects

Fertilizer Interactions

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Plant Stress & Diversity with Impacts on Insects

• Broadleaf herbicides placed on turf can have an adverse affect on trees

• Incidence this past year of a Dupont phenoxy herbicide had dramatic impact where used on nearby trees and shrubs

Herbicides

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Plant Stress & Diversity with Impacts on Insects

• The # of different types or species of organisms in a defined space.

• The # of species that dwell in a habitat.• Native plant communities can maximize the diversity of

animals verse exotic species.• These environments are more stable and less prone to

disruption.

How Do We Define a Diverse Landscape?

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Plant Stress & Diversity with Impacts on Insects

• If you count all the terrestrial bird spp in North America that rely on insects & other Arthropods to feed their young, it would be around 96%.

• These insects would also be among those harmful to ornamental plants.

Why Insects are Essential

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Plant Stress & Diversity with Impacts on Insects

• Most insects have very specific and restricted diets and won’t develop relationships with exotics.

• Therefore, these exotics won’t serve as sources of food within the food chain.

• e.g. Tent Caterpillars feed within Rosales.

Why the Need for Natives?

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Plant Stress & Diversity with Impacts on Insects

Eastern Tent Caterpillars

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Plant Stress & Diversity with Impacts on Insects

• Complex habitats contain more natural enemies because these plant species varied in Size, Shape, and Structure. This verses simple habitats.

• e.g. Azalea Lace Bug controlled in complex systems.

Conclusions?

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Plant Stress & Diversity with Impacts on Insects

Azalea Lace Bug

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Plant Stress & Diversity with Impacts on Insects

• Buddleia only attracts adults.

• Asclepia tuberosa, syriaca, incarnata all allow larval stages to

develop.

• Approx 11 Lepidoptera reproduce on Milkweed.

Gardening for Butterflies

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Plant Stress & Diversity with Impacts on Insects

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Plant Stress & Diversity with Impacts on Insects

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Plant Stress & Diversity with Impacts on Insects

Gardening for Butterflies

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Plant Stress & Diversity with Impacts on Insects

• Echinacea• Rudbeckia• Cephalanthus• Eupatorium fistulosum• Quercus• Cornus florida• Liquidambar styraciflua• Magnolia species

Other Lepidoptera agents in the Landscape

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Plant Stress & Diversity with Impacts on Insects

Those specialized at eating aphids:

• Ladybird Beetles• Syrphid Flower Flies• Chrysopid Lacewings• Bats & Dragonflies

Aphids as Specialized Predators

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Plant Stress & Diversity with Impacts on Insects

Monocultures

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Plant Stress & Diversity with Impacts on Insects

• Use of Shade Trees• Use of Small Flowering Trees• Use of a Shrub Layer• Groundcovers • Native Ornamental Grasses• Perennials• Add “Structure” like boulders, etc

How Can We Create Diversity?

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Plant Stress & Diversity with Impacts on Insects

• Woodland Landscapes• Meadow Landscapes• Bird and Butterfly Gardens• Rain Gardens• Water Gardens

Landscape Models

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Plant Stress & Diversity with Impacts on Insects

• Architecture of the Property:

– Create a layered approach to create a more suitable environment for natural predators to flourish.

Principles for the Home Landscape

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Plant Stress & Diversity with Impacts on Insects

• Canopy• Mid-level or Understory Trees• Shrub Layer• Herbaceous Layer• Ground Layer• Vines

Layers in the Landscape

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Plant Stress & Diversity with Impacts on Insects

Canopy Layer

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Plant Stress & Diversity with Impacts on Insects

• Liriodendron tulipifera• Fagus grandifloia• Quercus prinus• Acer saccharum• Acer rubrum• Nyssa sylvatica

Canopy Layer

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Plant Stress & Diversity with Impacts on Insects

Canopy Layer

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Plant Stress & Diversity with Impacts on Insects

Canopy Trees

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Plant Stress & Diversity with Impacts on Insects

• Cornus florida• Carpinus caroliniana• Amelanchier species• Cornus alternifolia• Asimina triloba

Understory Trees

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Plant Stress & Diversity with Impacts on Insects

Understory Trees

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Plant Stress & Diversity with Impacts on Insects

Cornus florida

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Plant Stress & Diversity with Impacts on Insects

Asimina triloba

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Plant Stress & Diversity with Impacts on Insects

• Lindera benzoin• Viburnum acerifolium• Calycanthus floridus• Kalmia latifolia• Rhododendron spp

Shrub Layer

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Plant Stress & Diversity with Impacts on Insects

Shrub Layer

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Plant Stress & Diversity with Impacts on Insects

• Mertensia virginica• Carex pensylvanica• Fern spp• Asarum canadense• Aster divaricatus

Herbaceous Layer

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Plant Stress & Diversity with Impacts on Insects

Herbaceous Layer

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Plant Stress & Diversity with Impacts on Insects

• Mosses• Rotting wood and debris• Organic matter• Leaf litter

Ground Layer

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Plant Stress & Diversity with Impacts on Insects

Varying the types of inflorescences will attract a wider range of insect pollinators which may also double as predators:

– Spikes– Raceme– Panicle– Umbel– Composite

Types of Inflorescences

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Plant Stress & Diversity with Impacts on Insects

Spike Inflorescence

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Plant Stress & Diversity with Impacts on Insects

Raceme Inflorescence

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Plant Stress & Diversity with Impacts on Insects

Panicle Inflorescence

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Plant Stress & Diversity with Impacts on Insects

Umbel Inflorescence

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Plant Stress & Diversity with Impacts on Insects

Composite Heads

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Plant Stress & Diversity with Impacts on Insects

• Create layers in the landscape incorporating regional natives

when possible. These regional natives are more likely to

develop natural soil partners.

• Use varying types of inflorescences.

• Reduce stresses by planting trees to produce shade.

Summary