Parasitoids and Parasitoidism Pages 110114

1
Parasitoids and Parasitoidism (Pages 110-114)
Parasitoidism is restricted to seven orders of
Holometabola. It arose independently on about 20
occasions. In most cases it seems to have arisen
from predation by specialization on large,
defenseless and often immobile prey. First sure
parasitoid is a mymarid wasp from about 100 mya.
(Possible parasitoid from 150 mya.) About
100,000 species of insects are parasitoids.
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Occurrence and Abundance of Parasites
Order No. of Origins No. of
Species Neuroptera 1 190 Coleoptera
6(?) 5400 Strepsiptera
1(?) 300 Trichoptera 1
1 Lepidoptera 1 or 2 300 Diptera
10(?) 11,000 Hymenoptera 1
85,000 Total approximately 102,000 species of
parasites
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Parasitoids and Parasitoidism (Page 110)

• Two patterns emerge
• 1. Less mobile females in the first five orders
  tend to deposit the egg(s) in the host
  habitat.
• Larvae, often hypermetamorphic, locate the
  host.
• Most Diptera and Hymenoptera (strong,
  maneuverable fliers), the female deposits the
  egg on or near the host.
• The greater mobility of the adult female accounts
  for thenumerical dominance of the Diptera and
  Hymenoptera among parasitoids (96,000 of 102,000
  species).

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Parasitoids and Parasitoidism (Pages 110 111)
Dominance of the Hymenoptera (85,000 of 102,000
species) retained ovipositor (to deliver the
egg onto or into the host) ovipositor allows
access to endophytophagous hosts ovipositor
allows wasps to assess host suitability oviposito
r delivers accessory gland fluid (toxins, etc.),
to condition the host, avoid encapsulation
(chemical mimicry, inactivate host immune
system, recall flies brute force, tear opening
in capsule) closely co-evolved host specificity
divides the range of potential hosts into
narrower niches developed petiole to use
ovipositor effectively
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Parasitoids and Parasitoidism (Pages 110 111)
petiole
petiole
petiole
accessory gland
Hymenoptera Ichneumonidae Adult female with
detail of petiole and ovipositor
OvipositorX-section
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Parasitoids and Parasitoidism (Page 111)
Variations on the theme Microtype eggs Known in
Tachinidae, Ichneumonidae and Trigonalidae Female
s lays many minute eggs on foliage Eggs consumed
by caterpillar with leaf tissue Larva hatches in
caterpillar gut, enters hemocoel Depending on
the species Attacks caterpillarAttacks vespid
larva that eats caterpillarAttacks ichneumonid
larva in caterpillar as hyperparasite
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Parasitoids and Parasitoidism (Page 112)
Variations on the theme Adelphoparasitism Known
in Hymenoptera Aphelinidae Females develop as
primary parasitoids of armored scales Males
develop as secondary parasitoids of females
(sisters) May help avoid overexploitation of
host population Complicates rearing in the
insectary, need many hosts
2N (female) larva endoparasite of the scale
insect
1N (male) larva ecto-hyperparasite of the female
wasp larva
Wax shield over scale
Body of scale
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Parasitoids and Parasitoidism (Pages 112)
Variations on the theme Heteroparasitism Known
in Hymenoptera Aphelinidae Inseminated females
deposit 2N eggs in scales or whiteflies Uninsemin
ated females deposit 1N eggs in moth
eggs Increases number of hosts available and
thus, wasp population Complicates rearing in the
insectary need two hosts, need two host
plants Discovered during a biological control
program
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Parasitoids and Parasitoidism (Page 112)
Variations on the theme Heteroparasitism Behavio
ral changes in the female wasps with
insemination change host habitat
finding change host finding change host
acceptance May change host suitability for
larvae Where do males and females meet?
male progeny
uninseminated female
moth egg
female progeny
whitefly
inseminated female
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Parasitoids and Parasitoidism (Page 112)
Variations on the theme Polyembrony Known in
several groups, notably Encyrtidae Involves
division of an embryo to yield 2 identical
progeny (the number of progeny varies from 2 to
about 500) The extreme cases among the
Encyrtidae, e. g. Copidosoma spp. that attack
caterpillar hosts are most interesting.
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Parasitoids and Parasitoidism (Page 112)
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Variations on the theme Polyembrony Female wasp
deposits egg in an egg Chorion
disappears Cell and polar body divide 1
morula syncitium Syncitium incises 2
morulae in polygerm Polygerm absorbs nutrients,
cells multiply Morulae develop into embryos
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Parasitoids and Parasitoidism (Page 112)
Variations on the theme Polyembrony Larvae
rupture polygerm feed in host body Larvae
pupate, filling host body Adults emerge
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Parasitoids and Parasitoidism (Page 112)
Variations on the theme Polyembrony A variation
on a variation- In some polyembryonic encyrtids,
a few larvae develop early(thus called
precocious larvae). These larvae are sclerotized
and mandibulate to physically defend the other
larvae (thus called defender larvae).Defender
larvae never mature.
Precocious and Normal larvae of a
polyembryonic encyrtid wasp
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Parasitoids and Parasitoidism (Page 112)
Variations on the theme Polyembrony A final
complication- If two females oviposit in the
same host or if a female deposits both haploid
and diploid eggs, cells from the two polygerms
may intermix during morula formation.This
yields chimeric individuals. If one egg was
fertilized and the other was not, the products
of the mixing are intersexes. They are often
also deformed , e. g. cycloptic (one eye, one
antenna).
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Parasitoids and Parasitoidism (Page 113)
Variations on the theme Phoresy Phoresy is
hitchhiking one organism rides on
another. Adult phoresy is less common, but is
known. (Most adults are alate and can travel
efficiently.) Larval phoresy is quite common,
especially among hypermetamorphic taxa.
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Parasitoids and Parasitoidism (Page 113)
Variations on the theme Phoresy Rielia
manticida (Hymenoptera Scelionidae) is a small
wasp with a short ovipositor. Thus, to
parasitize mantid eggs, the female must oviposit
before the ootheca is formed. To accomplish
this, she rides under the wings of a female
mantid, waiting for the host to oviposit then
parsitizes the eggs as theyare laid.
Adult femaleRielia, to scale
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Hard, external layer
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Parasitoids and Parasitoidism (Page 113)
Variations on the theme Phoresy Larval phoresy
usually occurs in hypermetamorphic species,
often those that attack concealed or protected
hosts. Eucharitidae (Hymenoptera Chalcidoidea)
deposit eggs inplant tissues, usually a flower
bud. Hatching planidia are phoretic on adult
ants that come to the flower for transportation
to the ant colony. Once in the ant colony, the
planidium attacks an ant larva. Orasema spp. add
the variation of using a thrips as an
intermediate phoretic host to reach the adult
ant.
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Parasitoids and Parasitoidism (Pages 113 114)
Variations on the theme Hyperparasitism A
hyperparasite is a parasite of a
parasite. Hyperparasitism is usually rare, but
occurs in a variety of taxa fungi nematodes mi
tes insects Among insects hyperparasitoidism
occurs in Diptera (rare, 3 families) Hymenopter
a (common, 19 families)
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Parasitoids and Parasitoidism (Pages 113 114)
Variations on the theme Hyperparasitism Degrees
of hyperparasitism secondary attacks
primary tertiary attacks secondary
quaternary attacks tertiary (rare) Designating
the hosts quaternary parasite
tertiary parasite (primary host)
secondary parasite (secondary host)
primary parasite (tertiary host)
herbivore/predator (quaternary host)
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Parasitoids and Parasitoidism (Pages 113 114)
Hyperparasites may be obligatory or facultative.
Obligatory develop only as hyperparasites
Facultative develop as primary parasites or
hyperparasites Facultative parasites vary in
their tendency to function asprimary or
hyperparasites. Obligatory hyperparasites have
been sytematically excluded from introduction in
classical biological control programs. Some
facultative hyperparasites with a strong tendency
to develop as primary parasites have been
released when goodobligatory primary parasites
were not available. Need to know tendencies
within a family how to test the species of
interest
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Parasitoids and Parasitoidism (Pages 113 114)
Variations on the theme Hyperparasitism Hyperpar
asites are also often flexible in terms of
developingas secondary or tertiary parasites and
their host ranges are often broader than those
of strictly primary parasites. This likely
relates to the fact that the primary parasite
has debilitated the hosts immune system and
many hyperparasites are ectoparasitic on
the primary, both reducing the need for
closely co-evolved host specificity. Flexibility
in both regards is beneficial to the
hyperparasitoid because the number of
parasitized hosts is smaller than thethe total
number of hosts. The resulting food webs can be
complex.
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Parasitoids and Parasitoidism (Pages 113 114)
Variations on the theme Hyperparasitism The
following summarizes relationships between an
aphid, two species of primary parasitoids and
three species ofhyperparasitoids.
Aphidencyrtus sp.
Hyperparasites(secondary ortertiary)
Pachyneuron sp.
Charips sp.
Aphelinus sp.
Diaeretiella rapae
Primary parasites
Herbivore
Cabbage aphid
Cabbage aphid
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Parasitoids and Parasitoidism (Pages 113 114)
Hyperparasites vary in how they attack their
host Direct hyperparasites oviposit only
if the primary parasite is already
present. Indirect hyperparasites oviposit
in any secondary host, but the resulting
larva will only develop if/when the primary
parasite also attacks the host. Direct
hyperparasitism Indirect Hyperparasitism
Primary parasite
Primary parasite
Secondary parasite
No secondary parasite egg deposited
moth
secondary parasite egg
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Parasitoids and Parasitoidism (Pages 113 114)
Hyperparasites vary in how they attack their
host Indirect hyperparasites waste many
eggs. They compensate by producing more
eggs But, host finding requires less time and
energy Thus, a cost/benefit balance is
achieved