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Friday, December 07, 2012
General Concepts of Biological Control
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General
Concepts of Biological Control
“Balance of Nature.” Virtually
all pest populations are affected by natural enemies to some extent. In many cases,
natural enemies are the primary regulating force of the pest populations. Natural
controls include effects of natural enemies (predators, parasites, pathogens), other
biotic (living) factors such as food availability and competition, and abiotic
(non-living) factors such as weather and soil.
IMPORTANT
CHARACTERISTICS:
a)
Often relatively inexpensive and can be “permanent”
for those biocontrol agents that can survive multiple years and become
self-perpetuating.
b)
Effectiveness can be from low to high.
c)
Can be disrupted by other pest management tactics,
especially broad-spectrum pesticides.
d)
Suppressive effects are density-dependent; it
will have its greatest impact when pest densities are high.
e)
Often pest-specific, not broad-spectrum.
f)
Often a lag time between buildup of the
pest population and buildup of the
biocontrol agent; generally not fast-acting.
g)
Good tactic to include in a multi-tactic
approach (IPM); fits in well with cultural, mechanical, and some
h)
chemical controls.
i)
Most successes have been in perennial crops (orchards,
vineyards), rangeland, and field or forage crops which can withstand a moderate
level of pest injury.
GENERAL METHODS
Biological control agents can be purchased from commercial suppliers
and released for supplementary
control of pests. However, most biological control occurs without
assistance from people. Many predators, parasites and pathogens occur naturally
and are continually working to help keep nature in balance. The importance of
natural enemies is often not appreciated until a broad spectrum pesticide,
which kills many beneficials as well as
the targeted pest, is applied and a new pest
– suddenly released from biological control – becomes a serious problem.
Conservation and enhancement of natural enemies already present in the system
can be a very effective method of biological control.
1.
Introduction = Importation
This is the “classical method” of using
biological control It has been used most for introduced or “exotic” pests. The
origin of the pest is determined and then a search or natural enemies in its
native habitat is conducted. Potential biocontrol agents are imported to the
new location of the pest and released. Generally, the hope is for permanent
establishment of the natural enemy.Classic insect example: In 1888, importation
of the Vedalia beetle (predaceous lady beetle) from Australia to California
citrus groves for control of the Cottonycushion Scale. The scale is native to
Australia.
2. Augmentation = Mass Culture or Collection and
Release
Inundative Release– a single release of large numbers of a natural
enemy; release can be in a small or large area; natural enemy does not become
established and reproduce; goal is a one-time reduction in pest numbers. Inoculative
Release– multiple, smaller releases of a natural enemy over a period of time;
natural enemy is expected to colonize and spread in the area of release.
3. Conservation
and Enhancement
Utilization of practices that protect, maintain and enhance already
existing natural enemy populations.
Such practices could include habitat diversification to provide
additional shelter or food for a natural enemy, provision of artificial food
supplements, use of pesticides that are selective for target pests and have
minimal effects on natural enemies, avoiding cultural practices that disturb or
destroy natural enemies, etc.
1. Parasites
and Parasitoids
Parasite– an organism that lives in or
on the body of another organism (the host) during some portion of its life cycle.
Parasitoid– an arthropod that parasitizes and kills another arthropod
(insects, mites, spiders, and other close relatives) host; a parasitoid is
parasitic in its immature stages and free living as an adult.Parasitoids have
been used in biological control more than any other type of agent. The major
types of insects that are parasitoids: wasps, flies, some beetles,
mantis-flies, and twisted-winged parasites. Adult female parasitoids lay their
eggs inside the host (the host arthropod is usually in its immature stage) by penetrating
the body wall with their ovipositor or they attach their eggs to the outside of
the host’s body.
2. Predators
Predator– “Free-living animal that feeds on other animals (prey); it
may attack prey in both its immature and adult stages; usually more than one
prey individual is required for the predator to complete its life cycle.”Major
types of animals that are predators: birds, fish, amphibians, reptiles,
mammals, arthropods, and some plants (e.g., Venus fly trap). Major types of
insects that are predaceous: dragonflies and damselflies, mantids, true bugs,
some thrips, lacewings and relatives, beetles, some wasps and ants, and some
flies. Spiders and some mites are also important predators of arthropods.
3. Pathogens
Use of microbial pathogens has become a very popular method of pest
management. Major pathogens used in biological control of insects:Bacteria–
Bacillus thuringiensis= Bt (many caterpillar pests, beetles, mosquitoes,
others).Viruses– Nucleopolyhedrosis viruses (Gypsy moth, European corn borer),
granulosis viruses (Codling moth).Fungi– Metarhizium(cockroach motels),
Beauveria bassiana (Colorado potato beetle, Corn rootworms).Protozoa– Nosema
locustae(grasshoppers).Nematodes – Steinernemaand Heterorhabditisspp. (Soil weevils,
Stem-boring caterpillars).
4. Herbivorous
Insects and Microbial
Pathogens of Weed Pests Numerous species of plant-feeding insects have
been evaluated for control of pest weeds. The greatest successes have been in
rangelands, forests, and other natural habitats where other weed control
approaches (e.g., herbicides, cultivation) are impractical or uneconomical.
Some pathogens have also been looked at as weed biocontrol agents (e.g., plant rusts).
The goal when using a weed biocontrol agent is generally one of weed population
reduction and not eradication. Importation of a biocontrol agent from the region
of origin of the weed has been the most common approach. It is generally a
long-term process which requires sustained efforts, but which can reap
long-term benefits.
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