Download 2 dic sess Insect-Microorganism

Insect-Microorganism-Plant
Interactions
2nd Discussion session
5th Lecture
1
Insect-Microorganism-Plant
Interactions
Fact
Insects and microorganisms require hosts.
2
Introduction
Mutualism
Parasitism
Insects + Micro
Plants
Directly or indirectly
interactions
3
Introduction
Mutualism
Parasitism
Plant + Micro
Insects
Directly or indirectly
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Plant-Microbes-Insects

When an insect touches a plant, it touches
Microbes (mainly bacteria) and their metabolic
products.
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Introduction


What are the benefits for microbes being on
plants.
House that may provide shelter, suitable
microclimate …etc for microbes
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Outlines
1- Endophytic Fungi
 2- Insect orientation by Bacteria
 3- Entomopathogens-insect-plant


interactions
4- Symbiotic bacteria in insects
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1
Endophytic Fungi
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Endophytic Fungi
The endophyte is actually a fungus that lives,
grows and thrives inside a host plant
Most terrestrial plants are colonized by one or
several species of endophytic fungi which can
be isolated from healthy-looking host tissue
Endophytes are contained within the plant
without disease. Plant tissues remain entire and
functional.
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Endophytic Fungi
The endophyte and the grass plant form a
mutually beneficial relationship; the plant
feeds and "houses" the endophyte while the
endophyte helps the plant survive insects, heat
and drought.
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Endophytic Fungi

Endophytes may upregulate host responses to
pathogens and pests. Chaetomium globosum
has been shown to increase host resistance to
rust and tan spot pathogens in wheat. Direct
interactions appear to be too small to measure
in this case. Presence of Lecanicillium lecanii
appears to reduce the feeding by aphids from
leaves of cotton
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Endophytic Fungi

Plants may benefit from the presence of endophytes
in many ways. Potential plant benefits have been
examined in only a few cases. Rhabdocline parkeri
produces a compound that reduces needle attack by
borers. Metabolites produced by Phomopsis sp in
cotton appear to deter larvae of Helicoverpa from
feeding on leaves. The parallels with Neotyphodium
are clear. In addition, aphids feeding on leaves of
cotton may become colonized by Lecanicillium
lecanii, when conditions permit. Thus the aphid may
be killed or it may transfer the fungus to another leaf
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2
Insect orientation by Bacteria
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Insect orientation by Bacteria

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Bacteria as adult food
Associated with oviposition site, host fruit
surfaces, and larval infested tissues
Bacteria orient fruit flies to the suitable host
Fruit flies-Bacteria-plant
interactions
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3

Entomopathogens-insect-plant interactions
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Entomopathogens-insect-plant
interactions
Plants can use entomopathogens as bodyguards
1) maintaining a population of bodyguards on
the plant surface,
(2) increasing contact rates between insect host
and pathogen and
(3) increasing the susceptibility of the host.
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Entomopathogens-insect-plant
interactions
Plants produce many secondary compounds that
confer protection against herbivore feeding (Karban
and Baldwin 1997). In addition to their direct effects
on herbivores, these compounds may interact with
bacterial, fungal, and viral pathogens of herbivores.
Secondary plant metabolites have shown both
synergistic and antagonistic effects on toxicity of B.
thuringiensissubsp. kurstaki against the gypsy moth.
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Entomopathogens-insect-plant
interactions
For example, oak (Quercus spp.) tannins, and conifer terpenoids
can decrease toxicity of B. thuringiensis subsp.
kurstaki against gypsy moths (Barbosa 1988, Appel and
Schultz 1994, Farrar et al. 1996). In contrast, activity
against larvae feeding on aspen (Populus spp.) increased
with increasing foliar levels of phenolic glycosides
(Hwang et al. 1995). Secondary metabolites
have been hypothesized to be responsible for the
relatively low activity of B. thuringiensis subsp.
kurstaki against gypsy moth larvae on willow (Salix
spp.) (Farrar et al. 1996).
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Entomopathogens-insect-plant
interactions
the fungal pathogen Beauveria bassiana sprayed
on to US corn was found to grow into the plant
and provide season-long control of corn borer
larvae ( Bing & Lewis 1991).
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Entomopathogens-insect-plant
interactions
Many plant traits will influence directly or indirectly the
survival of entomopathogens. Although certainly not the
only selection pressure on these traits, selection may
mould them to improve pathogen persistence. Examples
are canopy architecture, leaf form and leaf colour,
which can greatly diminish the harmful effects of UV
on these pathogen propagules. Other examples include
the density of hairs, waxiness, the veins, size and shape
of leaf, angle of the leaf to the stem, number of stomata
and density of the canopy, which will influence the
microclimate of the leaf, the thickness of the boundary
layer and the effects of wind and rain
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Entomopathogens-insect-plant
interactions
Aschersonia aleyrodis were found to retain
infectivity to whitefly much better on some
plants (e.g. cucumber) than others (e.g.
poinsettia).
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Entomopathogens-insect-plant
interactions
laboratory study by Ignoffo et al. (1977 ), who
demonstrated that soybean seedlings can pick
up spores of the fungus Nomuraea rileyi from
the soil and that these spores can subsequently
infect larvae of Trichoplusia ni (soybean
looper).
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Entomopathogens-insect-plant
interactions
Brown et al. (1995 ). The authors found that the
germination of conidia of the entomophthoralean
pathogen Pandora ( = Erynia) neoaphidis was
inhibited by volatiles released by tobacco plants in
response to herbivory by Myzus nicotianae (tobacco
aphids).
Germination would in this instance lead to the
production of secondary conidia, which would redisperse away from the leaf. Thus, the authors
hypothesized that the conidia "sit and wait" until they
are picked up, whereupon they germinate to infect the
aphid hosts.
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

Bacteria was sampled from fruit-free plants,
plants without fruits (just were harvested) and
plant with fruits.
Fruit fly Bactrocera proved an olfactory to
attract flies to the host plants
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Plant-mediated interactions between pathogenic
microorganisms and herbivorous insects
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Plant-mediated interactions between
pathogenic microorganisms and herbivorous
insects
Types:1.
Direct plant-mediated effect
2.
Locally plant-mediated effect
3.
Systemic effect
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Direct plant-mediated effect
Effect on antagonist 2 results from the physical
presence or activity of antagonist 1 and/or from
plant responses induced by antagonist 1
Some of these interactions are direct, for
example, when arthropods vector
phytopathogenic microorganisms
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Locally plant-mediated effect
Effect on antagonist 2 results exclusively from
plant response induced by antagonist 1. Both
antagonists are were present on the same
morphological entity of the plant (typically leaf)
The term local refers to interactions in which
pathogens and arthropods used the same plant
tissue at the same or different times
34
Systemic effect
Effect on antagonist 2 results exclusively from plant
response induced by antagonist 1. Each antagonist is or
was active on a different morphological entity of the
plant.
Indirect interactions between phytopathogenic
microorganisms and herbivorous arthropods can occur
when infection or infestation by a first attacker alters the
shared host plant in a way that affects a second attacker
that is often spatially or temporally separated from the
first

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Plant-mediated interactions between pathogenic
microorganisms and herbivorous insects
Objectives
plant-mediated interactions will facilitate an
understanding of how plants coordinate
and integrate their defenses against multiple
biotic threats.
36
The contemporary view of plant defense recognizes that
plants contend simultaneously with myriad attackers by
utilizing a multifaceted array of resistance mechanisms,
involving not only primary and secondary metabolites
and morphological and physicochemical traits, but also
mechanisms that allow plants to tolerate attack and
recruit the natural enemies of attackers
Recruit = to raise or strengthen
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FEEDING BY ARTHROPODS ON
DISEASED PLANT TISSUES
Interactions in which virus infection has a beneficial
effect on vectoring homopterans
are thought to reflect a mutualistic relationship between
virus and vector.
Data consistent with this hypothesis were presented, for
example, in a study
in which rates of increase of Myzus persicae on virusinfected potatoes were positively
correlated with the level of dependence of the virus on
the aphid for dispersal
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FEEDING BY ARTHROPODS ON
DISEASED PLANT TISSUES
Similarly, recent studies demonstrated that aphid
vectors such as Rhopalosiphum
padi and Sitobion avenae had greater preference
for, and higher fecundities
and rates of increase on, cereals infected with
Barley yellow dwarf virus than for
healthy cereals under laboratory conditions
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FEEDING BY ARTHROPODS ON
DISEASED PLANT TISSUES
Even in interactions in which virus infection has no net effect or a
net negative effect on vector population growth or fitness,
changes in vector settling or feeding behavior may be adaptations
to increase the spread of the virus
For example, the leafhopper Nepotettix virescens, a vector of
Tungro virus in rice, grew slower, fed less, was less fecund, and
experienced higher mortality on infected rice plants than on
uninfected plants. Despite this overall negative effect of infection
on leafhoppers, initial settling on Tungro-infected rice plants was
higher. The alterations in initial settling behavior and feeding
behavior were hypothesized to increase spread of the virus.
40
FEEDING BY ARTHROPODS ON
DISEASED PLANT TISSUES
Two studies have shown positive effects of systemic
virus infection on nonhomopteran arthropods. Survival
of Colorado potato beetle larvae was higher on
tomato plants infected with Tobacco mosaic virus
(TMV) than on healthy plants
Larvae of the Mexican bean beetle fed less and grew
slower on uninfected bean plants than on bean plants
infected with Southern bean mosaic virus or Bean pod
mottle virus (88). In the latter case, the insect vectors the
viruses.
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FEEDING BY ARTHROPODS ON
DISEASED PLANT TISSUES
The effects on arthropods of feeding on tissues
infected with pathogenic fungi
or bacteria can be positive or negative.
European corn borer larvae developed
approximately 20% faster on maize
showing symptoms of stalk rot caused by
Colletotrichum graminicola than on nondiseased
tissue
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FEEDING BY ARTHROPODS ON
DISEASED PLANT TISSUES
In contrast, systemic infection of Cirsium
arvense with the necrotrophic fungus Phoma
destructiva resulted in a number of
negative effects on the beetle Cassida
rubiginosa, including reduced oviposition,
feeding, survival, rates of growth, and pupal
weights
43
FEEDING BY ARTHROPODS ON
DISEASED PLANT TISSUES
One factor that appears to influence the outcome
of these types of tripartite interactions is the
constitutive quality of the infected plant for the
herbivore. The negative effects of rust infection
on larvae of Tyria jacobaeae were greater when
larvae fed on infected leaves of Tussilago
farfara, a poor host for this insect species, than
when larvae fed on rust-infected Senecio
jacobaea, a superior host
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FEEDING BY ARTHROPODS ON
DISEASED PLANT TISSUES
Similarly, the increase in relative growth rates
and fecundities of black bean aphids (Aphis
fabae) on bean leaves infected with the
necrotroph Botrytis fabae was greater on a
resistant bean variety than on a susceptible one
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PLANT-MEDIATED EFFECTS OF
PATHOGEN INFECTION ON INSECTS
Several other studies have investigated the
systemic effects of localized infection
by bacterial and fungal pathogens on subsequent
attackers. Again, both
positive and negative effects have been
demonstrated
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PLANT-MEDIATED EFFECTS OF
PATHOGEN INFECTION ON INSECTS
Localized infection of one leaflet on young tomato
plants with P. syringae pv. tomato resulted in 50% to
80% reductions in growth rates of the noctuid
Helicoverpa zea on the remaining leaflets of the
inoculated leaf. In contrast, infection of terminal leaflets
by the hemibiotrophic oomycete Phytophthora infestans
had no effect on leaf-systemic resistance to H. zea,
demonstrating again that infection by different
pathogens can
have different results for the same herbivore
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PLANT-MEDIATED EFFECTS OF
PATHOGEN INFECTION ON INSECTS
Infection of stems of peanuts with
the necrotrophic white mold fungus, Sclerotium
rolfsii, altered the resistance of
leaves to a leaf-feeding caterpillar, Spodoptera
exigua. Survival was∼20% higher, development
was faster, pupae were ∼25% heavier, and
feeding was greater on
diseased plants
48
PLANT-MEDIATED EFFECTS OF
PATHOGEN INFECTION ON INSECTS
Only a few studies have directly compared the systemic
effects of pathogen
infection on arthropods with local effects. Local effects
were usually stronger
than systemic effects
Local effects were usually stronger than systemic
effects. Weights of larvae and pupae were reduced and
development times were extended for the beetle
Phaedon cochleariae feeding on cabbage leaves
infected with the necrotroph Alternaria brassicae, but
the effects were not systemic
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PLANT-MEDIATED EFFECTS OF
PATHOGEN INFECTION ON INSECTS
Local effects were usually stronger
than systemic effects.Weights of larvae and
pupae were reduced and development
times were extended for the beetle Phaedon
cochleariae feeding on cabbage leaves
infected with the necrotroph Alternaria
brassicae, but the effects were not systemic
50
PLANT-MEDIATED EFFECTS OF
PATHOGEN INFECTION ON INSECTS
In addition, melon aphid (Aphis gossypii)
produced fewer offspring on diseased leaves
when leaves were almost completely necrotic,
but produced more offspring on diseased leaves
when symptoms were not as severe. No systemic
effects on aphid reproduction were observed. In
addition to showing the importance of spatial
scale, this latter study also shows the importance
of disease severity in determining effects on
herbivores.
51
PLANT-MEDIATED EFFECTS OF
ARTHROPODS ON PATHOGENS
Several recent studies have documented
increases in resistance to pathogens following
feeding by arthropods with a sucking mode of
feeding. Because sucking insects can induce
biochemical responses similar to those induced
by pathogens
52
PLANT-MEDIATED EFFECTS OF
ARTHROPODS ON PATHOGENS
Infesting rice plants with the white-backed
planthopper, Sogatella furcifera, dramatically
increased the resistance of plants
to rice blast, Magnaporthe grisea
53
In tomato, plants previously infested
with silverleaf whitefly, Bemisia argentifolii,
were more resistant to powdery mildew
(Erysiphe cichoracearum), but not to TMV, than
were control plants
54
Feeding by chewing insects can also influence
plant resistance to pathogens.
Feeding by H. zea on the terminal leaflets of
tomato leaves resulted in a 30% reduction
in lesion numbers caused by P. syringae on
undamaged leaflets of damaged
leaves
55
Several investigations of tripartite interactions
among pests of alfalfa have also
been conducted and again show the importance
of feeding type. Defoliation of
alfalfa by yellowstriped armyworms did not
affect severity of crown rot caused by
F. oxysporum
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Hatcher et al. (51) documented a plant-systemic
increase in the resistance of
Rumex sp. to the rust fungus Uromyces rumicis
following feeding by G. viridula
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MECHANISMS OF PLANTMEDIATED INTERACTIONS
Activation of Plant Response Pathways
DEFENSE SIGNALING IN PLANTS
SECONDARY METABOLITES
CROSS-EFFECTS
CROSS-TALK
Other Mechanisms of Plant-Mediated Interactions
CHANGES IN PRIMARY METABOLISM
PLANT STRESS-MEDIATED INTERACTIONS
CHANGES IN PLANT GROWTH AND MORPHOLOGY
INTERACTIONS MEDIATED BY NATURAL ENEMIES
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4
Symbiotic bacteria in insects
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Symbiotic bacteria in insects


symbiotic micro-organisms that provide the
insect with nutrients or detoxify plant
allelochemicals
They may expand the plant range of insects by
improving insect utilization of otherwise
marginal plants
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Symbiotic bacteria in insects

What bacteria do for the Insects.
A- Degradation of plant food
B- Synthesis of nutritional requisites that plants do
not provide at all or provide in insufficient
quantities (sterols, amino acids….
C- Detoxification of plant allelochemicals
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Symbiotic bacteria in insects
A comprehensive understanding of the
biology of insects requires that they be
studied in ecological context with
microorganisms as an important component
of the system
E.A. Steinhaus (1960)
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Symbiotic bacteria in insects
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