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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