insect biology entomology 2. phylum arthropoda largest phylum on earth –75% of all living species...
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Insect Biology
Entomology 2
Phylum Arthropoda
• Largest phylum on Earth– 75% of all living species
• Class Arachnida (spiders, ticks, scorpions…)
• Class Crustacea (shrimp, crabs, crayfish…)
• Class Insecta
• Class Diplopoda (millipedes)
• Class Chilopoda (centipedes)
Class Insecta
• Largest class of animals on Earth– ~800,000 species
• Over 200 million per person• History includes over 250,000,000 years of Earth
history• Many species still undiscovered• Populate EVERY habitat on Earth• Approximately 90,000 to 125,000 species in
North America alone
Class Insecta
• 3 body parts– Head– Thorax– Abdomen
• 6 jointed legs– 3 pairs on thorax
• Exoskeleton• 2 antennae• Compound eyes
Class Insecta
• Metamorphosis– Describes the way by which insects change, grow,
develop from egg to adult– All insects undergo some type of metamorphosis due to
exoskeleton– Referred to as “moults”– Many adults do not feed…adult phase for mating only
• Incomplete (12%) – Gradual change over time– Young looks similar to adult
• Complete (88%)– 4 distinct stages
Incomplete Metamorphosis
• Egg
• Nymph– Small adult– Lacks wings– Several stages
• Adult
Complete Metamorphosis
• Egg• Larva
– Worm like– Maggot, Caterpillar…– Molt several times
• Pupa– Cocoon
• Adult
Order Diptera
• “Two wings”
• Includes flies of all varieties, mosquitoes, gnats
• Many feed on rotting flesh or other decaying matter– Highly in tuned sense of smell is common
Order Diptera
• Forewings are membranous– Used for flying
• Hindwings are for balancing– “Halteres” – knob like
• Metamorphosis-Complete
• Mouthparts-sucking (most)– All forensically valuable species
Blow/Bottle Flies
Flies usually infest first because larvae (maggots) can survive in the liquid medium of the corpse.
Blow Flies
• Kingdom – Animalia
• Phylum – Arthropoda
• Class – Insecta
• Order – Diptera
• Family – Calliphoridae
• Genus– Cynomyopsis
• Species– cadaverina
Medicinal Uses of Maggots
• Well documented cases in medicine for centuries
• Maggots will selectively eat dead tissue before living tissue
• “Maggot therapy” is an accepted method for fighting infections– Now seeing a resurgence
due to MRSA*, etc.
WARNING – GRAPHIC IMAGES
*Methicillin-resistant Staphylococcus aureus
Maggots in leg amputation
Maggots in Wound
Maggots in small cavity wound
Order Coleoptera
• “Sheathed wing”• Largest group of insects
– 25% of ALL living species
• Includes the beetles and weevils• 350,000 known species• Forewings are hard; cover hindwings• Hindwings are membranous
– Used for flight– Wings meet in straight line down the middle of the back
• Metamorphosis-Complete• Mouth parts-Chewing• Usually eat the fly larvae rather than the corpse
Carrion Beetles• Kingdom
– Animal• Phylum
– Arthropoda• Class
– Insecta• Order
– Coleoptera• Family
– Silphidae• Genus
– Necrophila • Species
– americana
Determining Time of Death
• Known as Post-Mortem Interval (PMI)
• Use insect stage (instar) to determine the time since death– Maggots have 3 instars (or molts) before pupa
• Must consider:– Temperature– Time of day– Exposure of corpse (air, soil, water)
PMI Determination
• ID species– Different species usually arrive in specific
orders based upon senses
• Document larval length • Measure maggot size
• Determine instar– Can be determined by examining body
features
• Calculate PMI
Species Identification
• Look at structural differences– Body Shape– Color– Texture– Mouth hooks (at tapered end)– Spiracles (at blunt end)
Determine Instar
• Look at the Posterior End of maggot
• Breathing “spiracles” are located here
• Count the number of spiracle slits to determine the instar
Spiracle Slits
Spiracles used for breathing by the blow fly larvae.
Mouth Parts
Mouth hooks used by blow fly larvae to attach themselves to a food source. As a reminder, the larvae have no legs.
1st Instar
• 0-36 hours after eggs are laid
• 2 mm to 5 mm• 0 to 1 spiracle
slits
2nd instar
• 36-72 hours• 5 mm to 10 mm• 2 spiracle slits
3rd Instar
• 72 hour +• 15 mm to 20 mm
• 3 spiracle slits
Pupa
• Pupa cases usually found within a few feet of food source
• Cases can last for decades
Establishing Time of Death
Stages of Decomposition Experiment
WARNING – GRAPHIC IMAGES
Living Pig
0 to 3 days
Fly Eggs in EAR
Facts!
• In warm weather, maggots can digest 60% of a human body in less than a week!