Forest insects and pathogens:

ecology and management

byKristen Baker

Insect Feeding categories Foliage: defoliators, reduce capacity

for photosynthesis. Stems: bark beetles may kill whole

tree or individual branches Cone and seed feeders Twig and shoot insects: damage new

buds and growth Root insects

Biotic causes of plant disease Fungi - most common Nematodes Bacteria Viruses Protozoa Parasitic plants

The Disease Triangle

Amount of Disease

Pathogen

Host

Environment

Management and control options Chemical

– DDT, copper sulfates, botanicals Biological

– use of one organism to control adverse effects of another (natural enemies such as insect predators, viruses, pathogens)

Cultural– active management of vegetation to prevent

or reduce damage or decrease pest population

Integrated pest management Use of a combination of control

techniques that are ecologically, economically, and socially acceptable

Does not mean eradication necessarily, but reduction of pest to tolerable level

Native insects and pathogens Regulators of forest ecosystems

– cause mortality of weakest trees– create gaps within forest, increase

nutrient cycling, available light, insects may increase nutrient availability

– provide wildlife habitat (snags and downed woody debris)

Example: bark beetles Many species, some cause

widespread mortality of trees, others create small pockets of dead trees

Kill trees by mass attacking: many beetles attack the same tree and breed within the tree

Example: root diseases Fungi that cause tree decline and

death by attacking root system (disrupts water uptake by tree)

Often creates distinctive circular patches of mortality

Creates conditions for non-susceptible species to establish in forest

Exotic insects and pathogens Non-native to an area: abnormally

large amounts of mortality common Insects: natural enemies not present

in new location to control population Pathogens: no co-evolution for

genetic resistance to pathogen; long life span of trees a problem

Example: balsam woolly adelgid Native to central Europe; introduced

to North America ~1900 Adelges piceae Infests true fir (balsam fir, Frasier fir,

subalpine fir, grand fir) Feeding causes host to produce

“early heartwood”, reducing water transport.

Management and control Biological control

– insect predators, pathogens– limited success to date

Environment– cold winter temperatures– early or late frost

Example: white pine blister rust Introduced from Europe ~1900 Infects all 5-needled pines: sugar

pine, eastern and western white pine, whitebark pine

White pine blister rust

Whitebark pine (Pinus albicaulis) High elevations in the western US

and Canada Keystone species Mutualistic relationship

with nutcracker Wildlife dependence Restoration treatments

Example: sudden oak death

First reported in 1995, Marin County Widespread mortality of coast live

oak and tanoak Numerous other hosts: California

bay, buckeye, rhododenron Phytophthora ramorum: a fungus-

like organism (Oomycete).