Biological Control

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Biological Control

• Control of undesirable organisms through exposure
  to natural herbivores, predators, or pathogens
  (i.e. the next trophic level)
• Primarily used on non-native species or in
  agricultural situations

2
Biological Control

• Goal reduction of population sizes, not
  elimination
• Via reduction in density, seed production, and
  potential for spread
• Expensive to establish, but then needs little
  maintenance, may have lower negative effects than
  chemical control agents

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The Equilibrium Paradigm
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How it works

• Is the invasive an ecological or economic
  problem?
• Is there sufficient support to initiate a
  biocontrol program?
• If yes.

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How it works

• Locate candidate agents in native habitat
• Check for specificity of attack
• Lots of regulation, long approval process prior
  to release

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The situation in BC

• Crop losses due to weeds and control costs
  estimated at 50 million annually
• Weed control act duty of land occupier to
  control legislated noxious weeds
• BC uses 57 bioagents against 20 weed species

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St. Johns Wort, Hypericum perfoliatum

• Weed of rangelands
• Causes phototoxic response in grazing mammals
• Originally used chemical control, but
• St. Johns Wort was first plant to return
• Problems with leaching into other areas, lack of
  specificity of chemical agents

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St. Johns Wort

• Two defoliators, Chrysolina quadrigemina and C.
  hyperici, introduced in 1951
• No longer have economic effects, no longer spray
  herbicides
• Beetles do attack introduced ornamental Hypericum

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Tansy ragwort, Senecio jacobaea

• Alkaloids cause liver damage in grazing mammals

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Tansy Ragwort

• feeding by Longitarsus jacobae (Switzerland)
• invasive gt native

Stastny, Schaffner, Elle 2005
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Tansy ragwort

• Longitarsus not very effective in BC
• Working well in Oregon (below)

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Tansy ragwort

• Cinnabar moth, Tryia jacobaeae, also introduced
  in BC
• Combined agents showing some success near Nanaimo
• S. jacobaea continues to spread esp. after fires
  and along power lines

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Purple loosestrife

• Lythrum salicaria
• Alters hydrology, nutrient cycling
• Outcompetes native vegetation
• Reduces breeding sites of wetland birds

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Purple loosestrife

• Galerucella calmariensis and G. pusilla
  introduced for control (in BC, intro in 1992)
• Effective defoliators
• Plants are killed by heavy beetle attack.
• Has worked at many sites in B.C. and across
  northern North America
• Loosestrife often replaced by reed canary grass
  another invasive!

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Purple loosestrife
foliage removed Beetle attack
plant biomass
Data from Denoth and Myers 2004
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Gorse (Ulex europaeus)

• In parts of North America, gt90 seed predation,
  but no effect on invasiveness of weed
• Why are seed predators often chosen for
  biocontrol, and why might they be ineffective at
  control?

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Diffuse Knapweed
Cost 1 million/year in lost forage 1940 -
Penticton, Oyama, and Grand Forks
1970 - Thompson and Okanagan Valleys
1972 began biocontrol
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Larinus sp. Metzneria paucipunctella (larvae feed
on seeds)
12 different insects and a fungus have been
introduced for control!
(from Judy Meyers)
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Data Judy Myers
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When good bugs go bad

• Louda et al 1997. Science 2771088-1090
• Weevils (Rhynocillus conicus) released in Canada
  to control invasive thistles (Carduus spp.) in
  1968
• Subsequently released in US, now well established
  throughout North America

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When good bugs go bad

• Releases done even though weevils were found to
  use native thistles Cirsium, Silybum, and
  Onopordum (with oviposition preference for
  Carduus)
• Some native thistles are considered rare and are
  negatively impacted in US

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Evil Weevils?

• Increase in use of native plants by weevil
  biocontrol agent in US parkland

Abbreviations indicate native species and
location in parks
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Evil Weevils?

• A simple equilibrium that allows persistence of
  both a predator and a prey species not expected
  when the predator has multiple prey species
• Important to do both careful pre-release
  screening and follow-up work

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Biocontrol of plant pests

• Ladybugs, lacewings, parasitic wasps used in
  greenhouses and gardens for control of herbivores
• Large industry for rearing, dispersing
  biocontrol agents

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Conservation Biocontrol

• Manipulate environment to increase natural
  enemies, avoid using chemicals, especially in
  agroecosystems
• Habitat management may increase biodiversity

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Conservation Biocontrol

• Improve availability of alternative foods
  nectar, pollen, honeydew
• Provide shelter or benign microhabitat for
  overwintering or escape pesticides
• Provide habitat where alternate prey are present
• Provide temporal and spatial overlap in resources

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Conservation Biocontrol
Canola / Wheat adjacency syrphids in wheat had
canola pollen in guts aphid populations in wheat
tended to be lower
Rhodesgrass (Chloris gayana) in citrus orchards,
pollen is food source for predatory aphids of
herbivorous mites
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Effectiveness of biocontrol can depend on
landscape factors Border types affect Syrphid
movement
Phacelia
Traps
Wratten et al 2003 Oecologia 134 605-611
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Conservation biocontrol

• Some changes to traditional farming practices can
  reduce pest populations through consideration of
  ecology of their enemies
• Need enough benefit to justify taking land out of
  production or making other changes