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ingi agnarsson

on 27 November 2017

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Transcript of Holometabola

All insects that go through complete metamorphosis
Complete metamorphosis
Incomplete metamorphosis
COMPLETE metamorphosis thus a synapomorphy of the group
85% of all insects!
Where did the larvae come from?
Order: Neuropterida

Order: Mecoptera
Order: Diptera
Order: Strepsiptera

Order: Coleoptera

Order: Trichoptera
Order: Lepidoptera

Order: Hymenoptera
Order: Siphonoptera

Ancestrally, there were nymphs, but no larvae - as seen now in insects undergoing incomplete metamorphosis
Imaginal discs
Characteristics of larvae:
Soft bodied, slender
*Usually* 3 pairs of legs
No external wing buds
Sclerotized head capsule
Often reduced eyes
Where did the pupae come from?
During pupation larval cuticle is replaced by adult cuticle derived from 'IMAGINAL DISCS'

= ectodermal tissue of immature insects that develops into appendages and other parts of the adult cuticle

These are specialized cells under the cuticle that proliferate and differentiate during late larval and pupal stages
Imaginal discs have a predetermined develompental path - during metamorphosis they become whatever they are predetermined to be!
How do we know? How would you test that?
Nature, September 1999
Pronymph hypothesis
The pronymph hypothesis
Hemimetabolous insects:
The hypothesis that holo-metabolan larvae are an extended version of hemimetabolous pronymph
Pronymph a short lasting stage in hemimetabolous insect.
Larvae=pronymph, Pupae=nymph
Support for the pronymph hypothesis
Sclerotization similar in pronymph and larvae
IF (and it is an if) that is how, the next question is Why?
Niche partitioning of adult and young
Larvae are specialized feeding stages - some live inside plants, or in water. Adults specialized mating stages
Holometobolous insects have more control over develompent:
Can pupate quickly
Can enter a 'dormant' stage = diapause - e.g. many insects in VT overwinter as pupae (in diapause)
Major events in Insect Evolution
Full metamorphosis
WHEN did complete metamorphosis evolve?
This is the same as asking, how long ago was this node on the phylogeny
290-320 mya - maybe.....
Kukalova-Peck described a fossil 'larvae' but, maybe its a myriapod...
Yeates et al. 2012
300-350 myo
Holometabola major groups
1. Neuropterida - lacewings, dobsonflies, snakeflies
2. Coleoptera - beetles
3. Strepsiptera - twisted-wing parasites
4. Trichoptera - caddisflies
5. Lepidoptera - butterflies and moths
6. Diptera - flies
7. Siphonaptera - fleas
8. Macoptera - scorpion flies
9. Hymenoptera -
ants and bees
Raphidioptera - Snake flies

The only holometabola with active pupae
lacewings, ANTLIONS, and relatives (video)

Coleoptera - beetles!
Holometabolous Develompent
Morphological support is unclear,
some modifications of wings and
Eumetabola =
Holometabola + Paraneoptera
Synapomorphy: Folding of wings
All flying insects
Synapomorphy: wings!
4 ~equal sized wings with lots of veins
Elytra - heavily sclerotized forewings
for protection, not flight
Hindwings folded length+crosswise under Elytra
Abdominal sclerites heavily sclerotized
Protection, protection, protection!
Sucesss, success, success! 400.000 species
Coleoptera - beetles!
Four groups:

Small, not our focus:
Archosternata = wood borers
Myxophaga = Aquatic beetles
Two MAJOR groups:
Adephaga - predaceous ground and water beetles
Polyphaga - 90% of all beetles

45000 species
Aquatic = Hydradephaga
Ground = Geadephaga
Gluttonous feeders
Coxa fused, divides 1st sternite, trochanter extended

Also - pygidial glands in abdomen secrete defensive compounds
9 families - most diverse is Carabidae - common name Ground Beetles
Carabidae - ground beetles
Carabidae will be the most common Adephaga family you collect in VT
Antennae arise laterally - from side of the head

Sophisticated pygidial glands (e.g. Bombardier beetle)
The 'many-things eaters'
Very diverse with very diverse biologies

~320,000 species

Coxa not fused to thorax
Polyphaga vs Adephaga
Move them around, they still become what they were 'meant' to be
Both lack wing buds (nymphs and pupae have)
Both have reduced nervous system
Both have very high levels of Juvenile Hormone
she will not let anyone else see it...
However, in between egg and nymph there is a brief 'pronymph' stage, typically a soft bodied, 'helpless' stage subsisting on yolk...
3 Arthropod Diversity and Classification: Holometabola……………………... EI-9
5 Arthropod Diversity and Classification: Coleoptera/Strepsiptera................... EI-10
8 Arthropod Diversity and Classification: Panorpida ….................................... EI-12
10 Arthropod Diversity and Classification: Amphiesmenoptera ........................ EI-13
12 Arthropod Diversity and Classification: Hymenoptera I..…………………... EI-11
15 Arthropod Diversity and Classification: Hymenoptera II.……………………EI-11
17 Good vibrations: Arthropod communication: (guest lecturer L. May-Collado) .BB
19 Review for Exam II
22 Exam II
24 Arthropod Diversity and Classification: Arachnida I..................................BS-1+10
26 Arthropod Diversity and Classification: Arachnida II…............................BS-1+10
A couple others...
Carrion feederd - used in forensic entomology
Note clubbed antennae, often large, ~190 species
Rove beetles, very common, 46,000 species
Very easy to identify - SHORT ELYTRA
and elongate bodies
Soldier beetles
Very effective predators of aphids, grasshoppers, caterpillars and other things that eat crop. Excellent biological control agents
Very elaborate photic system
Species specific communitation between the sexes (males fly, females wait)
'Femme fatale fireflies'
Females of some species use aggressive mimicry to lure males of OTHER species and EAT THEM
Jewel beetles - many have elytra that are shiny and used in jewelry. Bullet-shaped.
Scarab beeltes and relatives, ~35,000 species
Typically robust with clubbed or lamillate antennae
Includes very large species (Hercules beetles) with sexual dimorphism (rhinoceros beetles), the dung beetles. White grub are larvae of these beetles
Blister beetles, produce defensive secretions -cantharidin- that cause blisters - used in medicine to remove warts
Elytra relatively soft and often short
Darkling beetles, 20,000 species of mostly black beetles
Larvae include 'mealworm' used as food for captive insectivores, Tribolium castaneum is a model organisms in ecology, several species are pests in cereal and flour storages
Weevils - over 40,000 species of 'snout beetles'
Long snouts - modified head, NOT a rostrum
Elbowed antennae. Relatively easy to identify

Include beetles that are social and can be pests on trees - bark beetles and ambrosia beetles
Leaf beetles - over 35,000 species, some of the most commonly encountered beetles
Many are pests, such as Colorado potato beetle, often very colorful
Longhorn beetles - 20,000 species with very long antennae
Many are pests in wood, damage wood and houses
The Titan Beetle is one of the largest insects (video)
Order: Strepsiptera
What is Strepsiptera related to?

Twisted wing parasites ~600 species
Very strange group - modification of first pair of wings into halters
Females look like larvae and live as parasites inside hosts
Very difficult to place phylogenetically - very unusual males, females lack adult characteristics, and their genomes are very unusual as well!
18S rDNA
modified elytra?
genomic data
the strepsiptera halters are forewings, the Diptera halters are hindwings
There are a lot of beetles...
Calopteron discrepans
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