Insect life-cycles

Question 1

The egg structure

Answer 1

• contains a micropyle - egg has an outer casing so sperm cannot easily penetrate - it is allowed in via this structure
• elements mean water cannot leave the egg and parts allow gaseous exchange

Question 2

Egg development examples

Answer 2

•maggots and flies need quick development - so lay advanced eggs
•botflies lay eggs in intermediate host, so need fast forming larvae from egg to burrow in skin
-larvae have backward facing hairs to stop falling out of a host

Question 3

Viviparity in insects

Answer 3

Giving birth to live young
•aphids - asexual reproduction
•can utilise ephemeral resources when they are abundance

Question 4

Post embryonic development terms

Answer 4

• instar = each phase of an insects growth
• Imago (or Imagine) - adult/final stage of insect development
• ecdysis occurs between each instar
• exuvia is the outer skin of the developing nymphs or pupae that will be shed

Question 5

Metamorphosis

Answer 5

Transition from 1 form to another
•most common - pupa to an Imago (complete transformation of its body plan)
•describes change from penultimate instar to Imago
•greatest change is the development of the wings

Question 6

Number of instars

Answer 6

•earlier insects have lots of instars
-mayflies have 30+ instars
•more recently evolved have less instars
•F tend to be bigger than M, cos they have ovaries etc.
-need more resources to produce this
-often F has more instars bc of this (in some spp)

Question 7

Ametabolism

Answer 7

Simplest form of development
•young are simply miniature adults, no body plan change
•adults continue to moult
•only Apterygotes
•adults and young live in same environment = competition
•adults distinguished by functional gonads and are sexually mature

Question 8

Hemimetabolism

Answer 8

Exopterygota
•nymphs are different to Imago
•wings form at end of transformation (have vestigial buds throughout)
•nymphs have wing pads
•1st instar recognisable as mini Imago though
•specious group
•stoneflies, dragonflies, cockroaches, crickets, grasshoppers and true flies

Question 9

Holometabolism

Answer 9

Endopteryogotes
•larvae to adult via pupa stage
•instars completely different to Imago
•go through different larval instars till pupal instar
•then metamorphoses into adult
•no wing buds - wings develop internally
•accounts for great success 
-larval forms and adults have completely different ecological needs, so no competition

Question 10

Larval phenotypes

Answer 10

Have different lifestyles

• differentiated by having legs and head definition in each individual type
  1. Oligopods - many legs, most underived and look nothing like larvae
  2. Polypods - many legs, more than 6 (not as much as before), caterpillars e.g.
  3. Apodous larvae - no legs

Question 11

Disadvantages of holometabolism

Answer 11

• requires lots of energy, lots of food and can cause mortality
• due to big change, pupa stage is longer and larvae are vulnerable to being killed
• delays reproduction

Question 12

Why don’t adults moult?

Answer 12

• wings form which cannot be shed during moulting - they don’t have a cuticle
• large energy expenditure for little benefit