Announcements Insect reproduction • Lab quiz next Monday • Types of offspring produced • Will cover same last two labs and two • Parthenogenesis field trips. • Paedogenesis • Know • Hermaphroditism in insects – insect internal anatomy • Effects of vertically transmitted – features of groups covered bacteria on reproduction – Information about aquatic insects covered in lecture and lab Example aphid life cycle Paedogenesis • Larval • Production of young by larvae • Loss of adult stage – Gall midges- eggs develop inside mother and consume her before emerging • Loss of pupal stage • Embryo formed in hemocoel of paedogenic mother-pupa • Adults emerge only when conditions are adverse to larvae Effects of vertically transmitted Hermaphroditism bacteria on reproduction-Wolbachia • Infects insect ovaries of • Rare, but occurs in Cottony cushion scale many orders • Females posess ovotestes • Passed onto next • Self fertilization generation through egg • Causes – Reproductive incompatibility between populations – Sex ratio distortion • Meiosis disturbed and females formed • Feminizes males into females 1 Insect growth Insect development • Kinds of growth Instar = stadium – Indeterminate – Determinate Imago = adult • Growth through molting – Membranes expand within instar – Growth when exoskeleton is soft just after molting Insect development Overall life history patterns • Ametabolous • Molt increment- increase in size between instars – primitive wingless groups • Factors influencing molt increments, intermolt – indefinite number of molts period, and number of instars • Hemimetabolous – Food supply – gradual change towards adult form – wings develop externally. – Temperature • Holometabolous – Sex – Non-feeding pupal stage present – Interaction between genes and environment – Develop wings and other adult structures internally during immature stages Overall life history patterns 2 Indeterminate growth Determinate growth • Continue to molt until death • Most insects • Collembola, Diplura • Distinctive instar marks end of growth • Apterygote Hemimetabolous Hemimetabolous • Stages • Egg, nymph, adult (no pupa) • In aquatic insects, immature called naiad • Nymph resembles adult but without wings • Exopterygote- wings develop on dorsal surface of thorax • Terrestrial • Adults and immatures often use similar habitats and food • Crickets, true bugs, cockroaches • Aquatic- dragonflies, mayflies, stoneflies 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 3 Larval types Holometabolous Thoracic legs Thoracic legs No legs Abdominal prolegs forwards head Flies, wasps, beetles Lepidoptera/sawflies Many orders, Predators, soil, dung, predatory beetles carrion Pupal types Pupae • Resting stage • Rearrangement of body into adult form • Sometimes enclosed in cocoon • At end, pupa encloses adult Most pupae Sclerotized cuticle Appendages loosely pressed to Appendages body cemented to body Ecdysis 4.