Transcript المحاضرة الثانية

‫المحاضرة الثانية‬
Insect-Plant Interactions
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Numbers of herbivorous species in
different orders
Insect
order
Total no. of
species
Herbivorous species
No.
%
349000
119000
119000
95000
122000
119000
35700
10500
35
100
30
11
Orthoptera
59000
20000
53000
19900
90
100
Tysanoptera
5000
4500
90
Phasmida
2000
2000
100
Coleoptera
Lepidoptera
Diptera
Hymenoptera
Hemiptera
HM
Specialization vs Generalization
Monophagous
Insects feed on one or a few closely
related species. Many lep. Larvae, hemi.
and coleopt.
Oligophagous feed on a number of plant
species belonging to the same plant family
example Pieris brassicae feeds on plant of
Brassicaceae
Specialization vs Generalization
Polyphagous
Insects feed on many plant species
belonging to different plant families.
Myzus persicae
Specialization vs Generalization
Limitations!
Limitations
Monophagous and Oilgophagous
 Individuals of the same insect species may show
different host-plant preferences in different area
of its distribution, and even individuals belonging
to same population may be much more
restricted in their choice.
 It is more convenient to distinguish only
specialist (Monophagous and Oilgophagous )
and generalist (Polyphagous)
Specialization vs Generalization



Host-plant specialization is the rule
rather than the exception.
An inventory (list) of about 5000
British herbivorous insects species
show that 80% of them should be
regards as specialists.
76% of all British aphids are
mnophagous, 18% are oligophagous,
and only 6% are polyphagous.
Specialization vs
Generalization
Generalists seem to be privileged
compared with specialists because
they have access to a much broader
food range!
BUT, specialists need to make decisions
based on a smaller number of options
than generalists, thereby increasing
the efficiency of decision-making
process in the former group.
Specialization vs
Generalization
Polyphahous insect species prefer
certain plant species. So they are
discriminate in what they choose from
their acceptable host plant range.
Oilgophagous species are
indscriminate….
Specialization vs
Generalization
The gypsy moth exhibits more
discrimination prefers full-grown
leaves, leaves grown on sunny side, in
southern side of tree
Age of the leaves
Exposed to sunlight
Direction
Specialization vs
Generalization
Specialization vs
Generalization
It has been argued that some polyphagous
insects should be considered as
monophagous when their host plant
selection based on a specific type of
plant chemical.
1.
Larvae of cabbage white butterfly feed on
plants of different families but they
contain glucosinolate. One can say that
cabbage white butterfly is monophagous
on glucosinolate-containing plants.
(Limitations!)
Specialization vs
Generalization
2- Similar, larvae of the brown tail,
Euproctis chrysorrhoea, attack trees
with tannins in their leaves.
(Limitations!)
Specialization on plant
parts
Specialization on plant
parts
Specialization on plant
parts
Food-plant range and host-plant range
Food-plant range and hostplant range
Oviposition female selects the plant on
which its offspring will feed
The diet breath of the larvae is often
wider than the range of plants
acceptable as oviposition substrate to
the adult female 2.6
Food-plant range and hostplant range
The oviposition female is governed by
different part of genome than those
coding to for food selection behaviour
in the larvae.
There is a positive correlation
between…..
Food-plant range and hostplant range
Different females of same population of the
butterfly Euphydryas editha showed host
different plant preference for oviposition.
Larval performance correlated positively
with it.
2
Tipworm Crovidosema plebbejana on different
plant stages of cotton and Malva showed
that there is a strong correlation between
the acceptable level of a plant as an
oviposition substrate and larval
performance.
2.7
Food-plant range and hostplant range
Thus, larvae grew best on the plants
that their mothers had selected.
Specialization on plant
parts
In addition to host plant specialization, also show
specialization with regard to the feeding sites they
occupy on their host.
different leaf parts taste different and possess
different physical properties.
Grass hopper many lepidoptera and Coleoptera larvae are leaf
foragers (folivores), ingesting large chunk of leaf material.
Plant bugs penetrate epidermal cell
Aphids suck from the sap flow in phloem
Leaf-hoppers tap (hit) the xylem
Leaf miners
HM
Specialization on plant parts
Compound leaves
Larvae of Catacala spp. Can discriminate
between the basal, alteral and
terminal leaflets of their compound
leaved food plant, and they showed a
dislike the basal leaflets.
2.10
Specialization on plant parts
Stem borers
Fig 2.11
Specialization on plant parts
Conclusion
These examples show how all parts of
plant are shared out and can support
some insect or others.
Below-ground herbivory
The total biomass of the life beneath our
feet is mach more than above the
ground.
The subterranean life of forest consists
of 100 000 to 500 000 insects and
other arthropods per square meter
Below-ground herbivory
The interactions of insect and plant
below ground surface are likely to
mirror the above-ground interactions.
Examples
Grubs eat rootlets
Larvae of onion flies, carrot flies, and
cabbage root flies are root borers.
Sap feeders like aphids
Below-ground herbivory
Root-infesting insect may affect their
above-ground counterparts (and vice
versa) via changes in their host's
chemistry and physiology.
The rice water weevils that feed on rice`
roots reduced the growth rate of the
fall armyworms.
Below-ground herbivory
Herbivore damage to roots may also
affect indirect plant defence.
Example
Cotton plants exposed to root-feeding
wirworms (Agriotes sp.) increased
their extrafloral nectar production 10fold. extrafloral nectar recruits
predators
Number of insect species per plant
species
No. plant species vs herbivorous insect species
An insect species occur on more one plant species.
Number of insects species attacking a single plant
species Not necessary competition
 Spatial separation
 Temporally separated because of differences in
phenology between insects
 Behavioral separations
Example
Plant of Urtica dioica is the host plant of eight species.
2.12
Number of insect species per plant
species
Number of insect species per plant
species
143 different insect species were found
upon Tansy Plant, Tanacetum vulgare,
Number of insect species per plant
species
Host Plant is more than food plants
Fed on
Lived on
Housing facilities provided by host plant:
biotic and abiotic factors other than
foods
Host Plant is more than food plants
Larvae of platyprepia virginalis were
parasitized by a tachinid fly in 83%
and in 50% on hemlock and lupin
plants in the same habitat,
respectively.
The avoidance reaction
Host Plant is more than food plants
hemlock plant
Apiaceae or Umbelliferae
lupin plant (legume)
Host Plant is more than food plants
Nutritionally optimal host
Nutritionally suboptimal host
survival rates
Host Plant is more than food plants
Nutritionally optimal host
Nutritionally suboptimal host
Insect may prefer the suboptimal host
that not visited by some of their
natural enemies. Such plant provide
better overall survival rates
Host Plant is more than food plants
Microclimate around plants
The upper leaf surface may be warmer
or cooler than ambient level,
depending on the rate of transpiration.
The lower surface of a leaf is usually
cooler and more humid than the upper
surface
Host Plant is more than food plants
Microclimate around plants
The temperature of the leaf surface may
be up to 10 c, and even more, above
or below the air temperature.
Fig 2.15; Table 2.6
Host Plant is more than food plants
Microclimate around plants
The microclimates may also be studied
at level of whole plants or within
natural vegetations
Fig. 2.16 2.17