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Announcements• Lab quiz next Monday• Will cover same last two labs and two
field trips.• Know
– insect internal anatomy– features of groups covered
– Information about aquatic insectscovered in lecture and lab
Insect reproduction• Types of offspring produced• Parthenogenesis• Paedogenesis• Hermaphroditism in insects• Effects of vertically transmitted
bacteria on reproduction
Example aphid life cycle Paedogenesis• Larval
• Production of young by larvae• Loss of adult stage
– Gall midges- eggs develop inside mother and consumeher before emerging
• Loss of pupal stage• Embryo formed in hemocoel of paedogenic
mother-pupa• Adults emerge only when conditions
are adverse to larvae
Hermaphroditism• Rare, but occurs in Cottony cushion scale• Females posess ovotestes• Self fertilization
Effects of vertically transmittedbacteria on reproduction-Wolbachia
• Infects insect ovaries ofmany orders
• Passed onto nextgeneration through egg
• Causes– Reproductive incompatibility
between populations– Sex ratio distortion
• Meiosis disturbed and femalesformed
• Feminizes males into females
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Insect growth• Kinds of growth
– Indeterminate– Determinate
• Growth throughmolting– Membranes expand
within instar– Growth when
exoskeleton is softjust after molting
Insect developmentInstar = stadiumImago = adult
Insect development
• Molt increment- increase in size between instars• Factors influencing molt increments, intermolt
period, and number of instars– Food supply– Temperature– Sex– Interaction between genes and environment
Overall life history patterns• Ametabolous
– primitive wingless groups– indefinite number of molts
• Hemimetabolous– gradual change towards adult form– wings develop externally.
• Holometabolous– Non-feeding pupal stage present– Develop wings and other adult structures internally
during immature stages
Overall life history patterns
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Indeterminate growth
• Continue to molt until death•Collembola, Diplura•Apterygote
Determinate growth• Most insects• Distinctive instar marks end of growth
Hemimetabolous• Stages
• Egg, nymph, adult (no pupa)• In aquatic insects, immature called naiad• Nymph resembles adult but without wings
• Exopterygote- wings develop on dorsal surfaceof thorax
• Terrestrial• Adults and immatures often use similarhabitats and food• Crickets, true bugs, cockroaches
• Aquatic- dragonflies, mayflies, stoneflies
Hemimetabolous
Hemimetabolous nymphs Holometabolous• Stages
– Egg, larva, pupa, adult– Larval stages looks very different than adult– Larvae often use different habitats and eat different
food than adults• Adult structures found in larvae as 'imaginal
disks'• Endopterygote- wings develop in invaginated
pockets of integument• Bees, wasps, butterflies, beetles, flies,
caddisflies
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HolometabolousLarval types
Predators, soil, dung,carrion
Many orders,predatory beetles
Lepidoptera/sawfliesFlies, wasps, beetlesforwards headAbdominal prolegs
No legsThoracic legsThoracic legs
Pupae
• Resting stage• Rearrangement of body into adult form• Sometimes enclosed in cocoon• At end, pupa encloses adult
Pupal types
Appendagescemented to body
Appendages loosely pressed tobody
Sclerotized cuticleMost pupae
Ecdysis
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