Conservation of Natural Enemies Pages 150157

1
Conservation of Natural Enemies (Pages 150-157)
Read Chapter Chapter 7 in Van Driesche and
BellowsSee also Barbosa. 1998. Conservation
Biological Control Conservation biological
control is the least disruptive form of
biological control. It started slowly and is
still an emerging science. The fact that habitat
affected parasitoid communities emerged in the
gypsy moth program (1911). The idea that this
could be used to enhance biological control did
not emerge in print until Flanders 1940. The
first paper to discuss possible means of
enhancing biological control was Townes 1958.
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Conservation of Natural Enemies (Pages 150-157)
I believe that the success and ease of classical
biological control dissuaded workers from taking
on the challenges of conservation of natural
enemies. There are many unknowns and challenges
to confront, but we are facing them now. The
greater restrictions on importations is one
factor contributing to the development of
conservation BC.
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Conservation of Natural Enemies (Pages 150-157)
Four basic concepts 1. Conservation is useful
where a potentially effective natural enemy is
rendered ineffective by environmental factors. 2.
Conservation is useful where pests are not
adequately and cost-effectively controlled by
other means. 3. Conservation is useful where
other control tactics disrupt the environment. 4.
Growers and buyers must accept the quality and
price of the product. These tenets guide you to
questions that must be answered as you begin a
conservation program.
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Conservation of Natural Enemies (Pages 150-157)

• Basic entomological questions
• Are there potentially effective natural enemies
  int eh agro-ecosystem?
• Are there potentially effective natural enemies
  near the agro-ecosystem?
• Answering these questions is a multi-step
  process.
• If the answer to either is yes, additional
  questions carry you through a program.

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Conservation of Natural Enemies (Pages 150-157)
Outline of a conservation program (Pages
151-152) 1. Sample local natural enemy
guilds 2. Identify natural enemies 3. Study
potentially effective natural enemies 4.
Determine habitat requirements of high priority
nat. en. 5. Determine if limiting factor(s) can
be moderated 6. Conduct field experiments to
test feasibility 7. Deliver information to peers
and growers
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Conservation of Natural Enemies (Pages 150-157)
1. Sample local natural enemy guilds Multiple
sampling techniques best consider the pest,
sample appropriately, sweep net for aphid
predators picking mummies for aphid
parasitoids pitfall traps for predators of
root-feeding beetle larvae 2. Identify the
natural enemies Same challenges as in
classical BC many taxa encountered sort to
morphotaxa determine taxa as best you
can prioritize taxa on knowledge of what family
does get expert determinations on possibly
important taxa
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Conservation of Natural Enemies (Pages 150-157)
3. Study potentially effective taxaprioritize
taxa for study based on knowledge of familytest
taxa in lab to verify pest consumptionobservation
s to see if it occurs in the field prioritize
natural enemies for additional study 4.
Determine habitat requirements and limiting
factorswhat is known about related
speciesexamine nearby sites, is nat. en. more
abundant identify factors limiting nat. en . in
crop foods? insecticides? secondary nat.
en.? competition?
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Conservation of Natural Enemies (Pages 150-157)
5. Determine if limiting factor can be
moderatedis it possible?Is it cost
effective? 6. Conduct field experiments to test
feasibilityconfirm limiting factorstest
possibility of improving BCconduct larger scale
trials to test practicality 7. Deliver
information to peers and growers
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Conservation of Natural Enemies (Pages 150-157)
Conservation tactics fall into two categories
(Page 152)reducing direct mortality or
interferenceproviding supplementary
resources Other ideas have been suggested, but
none has been developed to a practical level.
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Conservation of Natural Enemies (Pages 150-157)
Reducing direct mortality or interference (Page
152) The logic is simple Reducing mortality
increases natural enemy numbers,improving
biological control Reducing interference
enhances natural enemy performance, improving
biological control. However, many factors can
kill or interfere with insects, so the applicable
tactics are diverse.
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Conservation of Natural Enemies (Pages 150-157)
Dust (Page 152) Can disrupt biological
control Best documented with scales and
spider mites Early studies in citrus and grapes
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Conservation of Natural Enemies (Pages 150-157)
Dust (Page 152) How/Why is biological control
disrupted? Natural enemies more active,
encounter more dust, can interfere with
searching Dust adsorbs epicuticular waxes,
killing small arthropods by desiccation, high
surface to volume ratio (primary
factor) Solutions Oiling or paving
roads Leave/add groundcover Adding windbreaks
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Conservation of Natural Enemies (Pages 150-157)
Cultural practices (Page 152) Pruning or
harvest can disrupt biological control
How?/Why? Natural enemies may be removed
or killed Solutions Situation
specific Identify the source of the
problem Determine an acceptable, cost effective
solution
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Conservation of Natural Enemies (Pages 150-157)
Cultural practices (Page 152) Pruning apples
to remove wooly apple aphid Removed Aphelinus
mali too Solution Store pruned material Return
it to orchard in the spring to re-inoculate
Aphelinus
Eriosoma adult
Eriosoma nymphs on apple
Aphelinus adult
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Conservation of Natural Enemies (Pages 150-157)
Cultural practices (Page 152) Harvesting
alfalfa Killed Aphidius smithi, disrupted pea
aphid control Solution Strip
harvesting Maintain microclimate and hosts for
parasitoid
Pea aphid
Aphidius smithi parasitizing a pea aphid
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Conservation of Natural Enemies (Pages 150-157)
Cultural practices (Page 152) Chemical pest
control Kills natural enemies too Solution Re
duce the number of sprays Reduce application
rates Time the sprays to minimize impact on
natural enemies Use alternate formulation, e.g.
granules in soils Use selective insecticides
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Conservation of Natural Enemies (Pages 150-157)
Cultural practices (Pages 153-155) Host plant
resistance, incl. genetically engineered
crops Impact varies greatly with type of
resistance (tolerance, antixenosis,
antibiosis) with the nature of
resistance (physical, chemical) with pest
and natural enemy (which is more strongly
impacted by trichomes, does the chemical pass
through to the natural enemy) Solution Varie
s, covered in HPR class
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Conservation of Natural Enemies (Pages 150-157)
Providing supplementary resources (Pages
155-157) Host/Prey (Page 155) If
host/prey scarce Inoculate host/prey into the
field to sustain nat. enemies Often done
early in season, can be done later
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Conservation of Natural Enemies (Pages 150-157)
Providing supplementary resources (Pages
155-157) Russian wheat aphid program in
Idaho Hard to establish Aphelinus asychis wasp
active early season, before pest
abundant Solution Release Russian wheat aphids
at wasp release site early in season
Russian wheat aphid, Diuraphis noxia
Aphelinus asychis antennating Russian wheat aphid
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Conservation of Natural Enemies (Pages 150-157)
Providing supplementary resources (Pages
155-157) Alternate Host/Prey If host/prey
scarce Inoculate alternate host/prey to sustain
nat. enemies Alternate host/prey may be added
into the crop field or in the vicinity of the
cropAppropriateness varies with mobility of the
natural enemy.
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Conservation of Natural Enemies (Pages 150-157)
Providing supplementary resources (Pages
155-157) Alternate Host/Prey Phytoseid mite
populations have been sustained to control
Tetranychus spp. spider mites by adding Minor
pest, e. g. Willamettte mite in grapesNon-pest
prey, e. g. tydeid mites in grapes
Vineyard Pytoseid eating spider mite
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Conservation of Natural Enemies (Pages 150-157)
Alternate Host/Prey (Pages 155-156) Grape
leafhopper, Erythroneura elegantula Anagrus epos
(HymenopteraMymaridae) parasitizes eggs of
several leafhoppers, incl. E. elegantula Grape
leafhopper serious pest in Central Valley
minor pest in Napa Valley. Why?
Grape leafhopper damage
Anagrus epos
Grape leafhopper nymph
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Conservation of Natural Enemies (Pages 150-157)
Alternate Host/Prey (Pages 155-156) Grape
leafhopper, Erythroneura elegantuladiapauses as
adults Anagrus epos (HymenopteraMymaridae)
overwinters in host eggs, needs alternate
hosts Dikrella cruenta, alternate host on
blackberriesoverwinters as eggssustains Anagrus
epos population if blackberries close to
grapes Thus, A. epos effective in small Napa
Valley vineyards, ineffective in largeCentral
Valley vineyards.
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Conservation of Natural Enemies (Pages 150-157)
Non-Host/Prey Foods (Pages 156-157) Cover crops
and inter-cropping (Page 156) Both can supply
cover for natural enemiesfoods for nat. en.,
often pollen and nectar (may also add
alternative host/prey) Clover between cabbage
plantsincreases Carabidae and Staphylindae
(Coleoptera) Syrphidae (Diptera) decreases
cabbage root maggot, Delia brassicae
(Diptera Anthomyiidae)
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Conservation of Natural Enemies (Pages 150-157)
Non-Host/Prey Foods (Pages 156-157) Cover crops
and inter-cropping (Page 156) Both can also
interfere with pest host finding Summary of
intercropping studies Herbivore populations
reduced 56 of cases increased 16 of
cases unchanged 28 of cases
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Conservation of Natural Enemies (Pages 150-157)
Non-Host/Prey Foods (Pages 156-157) Food Sprays
(Pages 156 157) Include sugars (sugar, honey,
molasses) protein (yeast or casein
hydrolyzate, Wheast) In conservation, food
sprays serve mainly as arrestants, during
periods when hosts/prey are scarce. The
searching natural enemy alters it search behavior
Staying in the area longer (hopefully until
pest builds up)
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Conservation of Natural Enemies (Pages 150-157)
Food Sprays (Pages 156 157) Adult green
lacewings, Chrysoperla plorabunda, increased in
alfalfa fields one day after spraying with
sucrose and water. Ladybugs, Coccinellidae, can
be aggregated with foods that include sugar and a
protein source. Chrysoperla
plorabunda Coccinella septempunctata Value
of food sprays is variable, depending on timing
of spray,arrival of pest and weather (rain
washes off food spray)
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Conservation of Natural Enemies (Pages 150-157)
Refugia (Page 157) Short-term refugiaMaintain
suitable microhabitat host/prey
availability Sustain natural enemy
population Come in many forms unmowed strips
within crop field, recall pea aphid unsprayed
portions of a field shelter belts near field
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Conservation of Natural Enemies (Pages 150-157)
Refugia (Page 157) Long-term refugia for
oversummering/overwinteringSupply diapause site
Sustain natural enemy
population Windbreaks, hedge rows, etc., with
perennial vegetation grass for cover dicots for
pollen and nectar trees for shelter and visual
cues Artificial refugia strips of corrugated
cardboard around tree trunks can harbor
beneficials diapause boxes for insects that
overwinter as adults, e.g. Chrysoperla,
Coccinellidae