Lecture 1 Pest Origins, Pesticides

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Definition and Scope of Biological Control
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Biological control the action of parasites,
predators or pathogens in maintaining another
organisms population density at a lower average
than would occur in their absence DeBach 1964
Includes natural and manipulated
Not resistance breeding, cultural,
semiochemicals, BT, sterile male
No implication of economic control
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Van den Bosch et al. modified the terms somewhat
and referred to Applied biological control as
the manipulation of natural enemies by man to
control pests and Natural biological control
as that control that occurs without mans
intervention
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Advantages of Biological Control

• high level of control at low individual cost
• self-perpetuating at little cost after initial
  effort
• very few harmful effects on man, environment etc
• some NEs reproduce rapidly
• some NEs search out hosts
• some NEs survive even at low host densities
• virtually unknown development of host resistance
  to introduced biocontrol agents (although new
  evidence suggests this might be possible)

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Limitations of Biocontrol

• Host population continues to exist at level
  determined by properties of host, NE and
  environment - may still be economically damaging
• establishment of biocontrol for one pest in a
  system necessitates integrated approach for all
  other pests in system
• research necessary to find BC solution may be
  demanding - no guarantee
• biocontrol successes have been rare in some
  fields such as control of plant pathogens, insect
  vectors of disease, medical etc.

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An integrated approach
Most Biocontrol practitioners agree - properly
used pesticides are a useful tool
The answer integrated approach to pest control
Pest population management - not preventative
treatment
Pest control ? pest elimination
Best controls are natural, self sustaining
Pesticide is the ultimate weapon - held in
reserve until absolutely necessary
Cannot manage for a single pest alone - manage
pest complex
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Types of Biological Control
Classical - involves importation and
establishment of new natural enemies to an area,
usually for exotic pests, occasionally for
natives
Conservation - enhance conditions for existing
natural enemy survival and reproduction
Augmentation - involves rearing and release of
natural enemies to supplement what is there or
when permanent establishment is not possible
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Origins of Pests
Indigenous (native) - organisms in a specified
area that evolved in that location
Endemic (precinctive)- indigenous organisms that
occur nowhere else
Adventive (exotic) - organisms in a specified
area that did not evolve there, but arrived from
somewhere else
Immigrants - those adventive species which were
not deliberately brought to the new area by man
Introduced - those adventive species which were
deliberately brought to an area by the conscious
choice of man
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Targets, and Agents of Biological Control
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Origins of Pests
Indigenous (native) - organisms in a specified
area that evolved in that location
Endemic (precinctive)- indigenous organisms that
occur nowhere else
Adventive (exotic) - organisms in a specified
area that did not evolve there, but arrived from
somewhere else
Immigrants - those adventive species which were
not deliberately brought to the new area by man
Introduced - those adventive species which were
deliberately brought to an area by the conscious
choice of man
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Targets of biological control

• Insects have been most common target
• worldwide apprx 550 sp targeted in gt1200
  programs of introductions
• homopterans have been most successful target
  (due to scale, aphid and whitefly movement
  internationally on plants in trade, and the
  importance of NEs in restraining densities)

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Targets of biological control (contd)

• Several families of Mites have been targets,
  including
• Rust mites (Eriophyidae)
• tarsonemid mites (thread footed mites)
• especially spider mites (Tetranychidae)

• Snails are the next most common invertebrate
  target
• either herbivorous sp. that attack crops or
• medically important sp. that are intermediate
  hosts for human or domestic animal pathogens

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Targets of biological control (contd)

• Feral populations of Vertebrates can become
  important pests in many systems
• problem is that they may be desirable in other
  contexts project must only be in area where
  domestic populations do not exist
• limited to pathogens with narrow host ranges,
  and genetically modified pathogens
• eg modified myxoma virus of rabbits causes
  females to develop antibodies against sperm

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Agents of biological control

• Parasitoids have been the most common type of
  natural enemy introduced for control of insects
• most parasitoids used are in the order
  Hymenoptera and to a lesser extent Diptera

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Agents of biological control (contd)

• While at least 26 families of parasitoids have
  been used, the most frequent Hymenopterans are
• Braconidae
• Ichneumonidae

• Eulophidae
• Pteromalidae
• Encyrtidae
• Aphelinidae

In the Diptera, the most frequent group has been
the Tachinidae
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Agents of biological control (contd)

• Predators are important control agents of both
  native and introduced pests
• There are 32 families that are significant for
  pest suppression, of these most common in crops
  are
• Anthocoridae (minute pirate bugs)
• Pentatomidae (soldier bugs)
• Reduviidae (assassin bugs)
• Carabidae (ground beetles)
• Coccinellidae (lady bird beetles)
• Staphylinidae (rove beetles)
• Chrysopidae (green lacewings)
• Cecidomiidae (predatory midges)
• Syrphidae (syrphid flies)
• Formicidae (ants)

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Agents of biological control (predators contd)
Spiders (Araneae) are virtually all predacious -
their role in pest suppression is becoming more
recognized
Predacious mites (Phytoseiidae) are important in
controlling spider mites
Fish (Gambusia affinis) have been used through
augmentative releases for the control of mosquito
larvae
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Agents of biological control (contd)
Pathogens and nematodes attacking arthropods

• These may be important natural sources of
  mortality for many species
• some have been commercially formulated and
  marketed as insecticides

• These include
• bacteria (esp. genus Bacillus)
• viruses (esp. Baculoviridea)
• fungi (esp. Entomophthoraceae)
• protozoa (including microsporidians)
• nematodes (esp Steinernematidae and
  Heterorhabditidae)