ENT 305 Life Cycles

Eggs

• Laid in clusters or singly, sometimes in cases

• Tiny but come in many shapes, colors, etc

• Often laid on, in, or near food

Eclosion

Hatching from the egg

Ootheca

Egg case in some insects (ex. cockroaches and mantises)

Chorion

Proteinous “egg shell”

Oviposit

Lay eggs

Larvipositing

• Lay larvae

• “Best parents”

• Includes flesh flies in the family Sarcophagidae and also Tsetse and some bot flies (the sheep bot)

Exoskeleton

• Fixed in size

• Incorporates the changes that are part of metamorphosis 

• Initially soft and is larger than the old exoskeleton

• Change in body form comes about as a series of steps called Metamorphosis

Metamorphosis

• A biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal’s form or structure through cell growth and differentiation

  • Allows growth

  • Allows specialization between stages

Ametabolous

 No change

• Minority of insects

• No metamorphosis, only change in size and genitalia as they age (only obvious difference between nymphs and adults)

• Wingless adults

• Variable numbers of instars and can sometimes even molt as adults

Hemimetabolous

Incomplete metamorphosis (without a pupa)

• Most insect orders

• Wings develop externally from “pads”

• Nymphs (if present in adult) have compound eyes

• Nymphs and adults live in the same habitat and eat the same food

• Major structural differences: Wings and genitalia

Holometabolous

Complete metamorphosis (with a pupa)

• Most insect species (includes most insects of forensic science importance)

• Pupal stage: where the most dramatic metamorphosis takes place

• Wings develop internally

• Larvae often wormlike and never have compound eyes

• Larvae are typically long lived and do the most feeding

• Adults are generally short- lived and will mate and disperse

• Adults and larvae tend to feed on different foods (exception: predators (like mosquitos))

Vermiform (Shape of larvae)

Body elongate, legless, worm-like (ex. maggots)

Scarabaeiform (Shape of larvae)

Curved, well developed head, thoracic legs (ex. beetles)

Elateriform (Shape of larvae)

Body elongate, cylindrical, hard, short legs (ex. Certain beetles)

Campodeiform (Shape of larvae)

Body elongate, flattened, cerci and antennae well developed (ex. caddisflies)

Eruciform (Shape of larvae)

Body cylindrical, head well developed, short antennae, thoracic legs and abdominal prolegs (ex. caterpillars)

Beetle larvae

Have legs and a head capsule

Pupa

The “inactive” stage in all holometabolous insects

• Final immature stage directly preceding adult stage

• Usually immobile and non-feeding and vulnerable

• Insect undergoes dramatic morphological change, gaining compound eyes, wings, and usually entirely new body shape.

• Fly pupal cases are important in forensics because they can help determine the PMI

• Flies pupate in their last larval “skin” called puparium

• Flies break out of their puparium by inflating a structure called a ptilinum on front of their head

Pupate

To become a pupa

Puparium

The exuvium of the third larval instar, within which the pupa is formed

Pupariation

The formation of the puparium

Chrysalis

The pupal stage of butterflies

Cocoon

Casing spun of silk by many moth caterpillars and numerous other holometabolous insect larvae as a protective covering for the pupa

Coarctate

Pupae are contained within the last larval exoskeleton, the puparium (ex. many diptera)

Exarate

Legs and wings are free from body and abdomen is moveable, limited locomotion (ex. many beetles)

Obtect

Wings and appendages are appressed to body and most of abdominal segments are immovable (ex. leps)

Order

Development conserved at this level

Immatures

• Nymphs/naiads: incomplete

• Larva/Larvae: complete

• Almost never have wings or genitalia

• Instar

Instar

A developmental stage of arthropods between each molt, until sexual maturity is reached. The number varies depending on the insect (3-15) and may change in repose to environment. (ex. blowflies have three)

Most Ametabolous and Hemimetabolous Life Cycle

Egg > Nymph 1 > Nymph 2 > Nymph 3 > Nymph 4 > Adult

Most Holometabolous

Egg > Larva 1 > Larva 2 > Larva 3 > Pupa > Adult