Transcript Natural enemies - University of Nebraska–Lincoln

grasshopper
Insect Damage
spider mites
potato beetle
aphids
Parasitoids
This wasp is laying its egg inside an aphid
where its young will develop. Parasitoid larvae
develop on or inside a host, killing it as they
mature. They emerge as adults and continue
the cycle.
Predators
A predator consumes many prey during its lifetime
Syrphids
Coccinellids
Chrysophids
Biological Control
1:170
1:70
30
Aphids
Syrphid : Aphid
Ratios
1989
• Temperature
dependent aphid
population growth
• Starvation of
syrphids
20
10
0
0
2
4
6
8
10
12
Days after Release
1991
Aphids
30
20
10
0
0
2
4
6
8
Days after Release
10
12
N-isoclines for different growth
rates of aphid population
3.19
Number of
Predators
2.72
1.06
1.02
1.01
Number of Prey
(Tenhumberg, Environ Entomol 1995)
How many predators do we need?
• Aphid density
• Aphid population growth rate
– Temperature
– Host plant (nutritional values)
• Predator species
–
–
–
–
How much do they eat
Temperature
Nutritional value of aphid
How quickly do the find and eat the prey
Temperature
Metopolophium dirhodum (Dean 1974)
Temp [oC]
10
15
20
25
30
Larval
mort. [%]
3.5
8
13
18.6
100
Adult
Fecundity
intrinic
lifespan [d]
growth rate
20
44
1.0
22
53
1.9
19
61
0.4
12
4
0.0
-
Easy estimates
Maximum number of aphids consumed during larval phase
Episyrphus balteatus
Aphid species
Sitobion avenae
Metopolophium dirhodum
Metopolophium dirhodum
Metopolophium dirhodum
Metopolophium dirhodum
Aphis fabae
Aphis fabae
Aphis fabae
Size
3rd
3rd
3rd
3rd
3rd
medium
medium
medium
Temp [oC]
17
14
17
20
22
15
20
23
No aphids
140
1113
1041
886
658
553
407
1322
Source
Ankersmit et al (1986)
Tenhumberg (1992)
Tenhumberg (1992)
Tenhumberg (1992)
Tenhumberg (1992)
Wahbi (1997)
Wahbi (1997)
Wahbi (1997)
Model System
Vicia faba
Hippodamia convergens
(holometabolous)
Acyrthosiphon pisum
(hemimetabolous)
Aphids
• 4,400 species of small insects
– 250 species are serious pests
• Aphids are divided up into 10 families all of
which have been extant for 50 - 70 million years
Superfamily Aphidoidea
Pemphigidae
Anoeciidae
Hormaphididae
Mindaridae
Thelaxidae
Lachnidae
Phloeomyzidae
Greenideidae
Aphididae
Drepanosiphidae
70% of species
Aphid Feeding
• Specialization
– Monophagous:
feeding only on 1 species of plant
– Polyphagous:
feed on hundreds of plant species
• How do they feed
– Passive feeding on sap of phloem vessels:
This sap being kept under high pressure,
once a phloem vessel is punctured, it is
forced into the food canal.
– Active feeding (sucking) from xylem vessels when
thirsty
• Virus transmission
Plant Tissues
• Xylem:
conducts water and
dissolved minerals from the
roots to all the other parts
of the plant.
• Phloem
– Sieve elements conducts the products of
photosynthesis - sugars and amino acids - from the place
where they are manufactured (a "source"), e.g., leaves, to the
places ("sinks") where they are consumed or stored;
– Companion cells move sugars and amino acids into and out of
the sieve elements.
Honeydew
Excretion of sticky
substance known as
"honeydew" which usually
becomes black with sooty
mold.
Aphid honeydew is rich
on carbohydrates (like
melezitose), of which the
aphids ingest an excess,
being phloem-feeders.
http://en.wikipedia.org/wiki/Aphid
Some species of ants
"farm" aphids, protecting
them on the plant they
eat, and eating the
honeydew that the aphids
secrete; this is a
mutualistic relationship.
Migration and Dispersal
• Most of the time aphids do not have wings, and in
general they move very little, and life consists of feeding
and giving birth.
• What stimulates movement
–
–
–
–
death of the host plant
danger
end of season
Winged forms (alatae) appear
overpopulation
• Short distance dispersal: 1.6 to 3.2 km per hour
• Long distance dispersal: >400 km in 9 hours
– Fly upwards to get above the planetary boundary layer (1000m
above sea level) and are carried by the low level jet streams
Reproduction:
• Thelytokous parthenogenesis:
Obligate parthenogenesis
where females give birth only
to female offspring
• Short generation time
(about 10 days on average)
• Telescoping of generations:
Grandaughters begin
developing directly within the daughters which
are themselves not yet born
Aphid Life Cycles
• Alteration of sexual and asexual generations
– Holocyclic
• Species that produce both sexual and asexual morphs
• Cyclical parthenogenesis: Many generations of asexual
(parthenogenetic) reproduction (all females), followed by
single generation of sexual reproduction
– Anholocyclic
• Species that produce only asexual morphs
– Although many species are either holocyclic or
anholocyclic, many other species possess both
holocylic and anholocyclic populations
• Host plant alternation
Holocyclic Species
• Asexual and sexual morphs are produced at different
times of the year.
• Males are present only in one part of the life cycle.
Viviparous females
(winged and unwinged)
Fundatrix
(usually unwinged)
Egg
(typically
overwintering)
Oviparous female
(unwinged)
Male
(winged and unwinged)
Anholocyclic Species
• No sexual males and females
• No direct descendants of the sexual morphs, namely the
egg and the fundatrix.
• Often no primary host.
Viviparous females
(winged and unwinged)
Viviparous females
(usually overwinter as
apterae or nymphs)
Host Alternation
• Autoecious: single host plant
• Heteroecious: alternating between host
plants
Primary host:
Shrub or tree
Secondary host:
Herbaceous plant
Acyrthosiphon pisum
• Common name: pea aphid
• Pink and green genotypes
(polymorphism)
• Green morphs suffer higher
rates of parasitism than red morphs
• Red morphs are more likely to be preyed on by
predators than green morphs are
• Reproductive rates of both morphs are the same
• Aphid defensive behaviour of both morphs is the
same.
A. pisum
Life Cycle
Acyrthosiphon pisum
• Distribution
Throughout the U.S. and
Canada
• Host Plants
Sweet peas, sweet clover,
alfalfa, and some leguminous
weeds.
Vetch and crimson clover are
important overwintering hosts
Plant Damage
• Extract sap from terminal leaves
and stems
• Feed on pods causing them to
curl, shrink, and partially fill.
• Feeding can result in
deformation, wilting, or plant
death
– Plants less than 15 cm (6 in) high
are easily killed by a few aphids,
whereas larger plants are only
slightly damaged.
Heavy infestations of pea aphid
have caused chlorosis
(yellowing) and wilting of plants
in this plot of susceptible alfalfa
• Coated with shiny honeydew
• Virus transmission, e.g. pea
enation mosaic and yellow bean
mosaic viruses.
Bean pod damage
Vicia faba
Lady Beetles
(Coleoptera: Coccinellidae)
• Over 450 species are found in North America.
Some are native and some have been
introduced from other countries.
• Food:
– aphids
– mites, small insects, and insect eggs
– plants
(Mexican bean beetle, Epilachna varivestis, squash
beetle, Epilachna borealis)
– Low food availability
• pollen, nectar
• cannibalistic
Aposematism
• Warning colors:
– Most predators associate bright colors (especially
orange and black or yellow and black) with poison
and other unpleasant properties.
• Toxin
– toxic to smaller predators, such as lizards and small
birds;
– Adults are able to reflex-bleed from their leg joints,
releasing their oily yellow toxin with a strong repellent
smell.
Adult Coccinellids
• Overwintering
– often in aggregations along
hedgerows, beneath leaf
litter, under rocks and bark,
and in other protected
places including buildings.
• Migration
– In spring, the adults
disperse in search of prey
and suitable egg laying
sites.
Hippodamia convergens
(1-2 generations / year)
Predation efficiency
(H. convergens)
•
•
•
•
Activity period: late spring-early fall
Consumption
Cannibalism
Fecundity (no. eggs) and fertility (fertile
eggs)
• Migration
• Pesticide application
References
• Dixon, A.F.G (1998): Aphid Ecology,
Chapman and Hall, London, UK, pp.300
• Hodek, I. and A. Honek (1996): Ecology of
Coccinellidae, Kluwer Academic
Publishers, The Netherlands, Dordrecht,
pp. 464
Lab overview
• Parameter estimation for aphid model
– Developmental time
– Survival
– Fecundity
• Testing predicted aphid population growth
rate
• How much do predators eat?
– Maximum aphid consumption at different
developmental stages
Aphid Experiments
Model
600
500
400
300
200
100
0
Total Population
Asymptotic Growth
Maximum Transient
1
2
3
4
5
6
7
8
9 10
12
Time [days]
14
16
18
20
H. convergens
• Access food
– Larva:
> 20 aphids/day
– Adults:
> 50 aphids/day