Download Development & Reproduction

Development
larva or nymph passes through several
instars
L1, L2, L3, L4, L5, etc. or N1, N2
Development
Two principal types of metamorphosis in
insects:
Incomplete or Hemimetabolis
&
Complete or Holometabolis
Hemimetabolis
• Wings develop externally
• No prolonged resting stage (pupa)
before last molt
• Typical of more primitive insects
Hemimetabolis
• Immature similar in appearance to adults
Called nymphs
Hemimetabolis
• Compound eyes are present in nymph
if
• They are present in the adult.
Hemimetabolis
• If adult forms are wingless,
• Nymphs will differ in size and sexual
development
Hemimetabolis
• If adults are winged, wings on
immatures appear as budlike
outgrowths
• Increase in size slightly until last molt
• After last molt, wings expand to full
adult size
Egg
Hemimetabolis
Nymph
Adult
Holometabolis
• Early instars are caterpillars or wormlike called larvae
• Different larval instars usually similar in
form but differ in size
• Resting stage precedes last molt
• Characteristic of more recent insects
Holometabolis
• Immature and adult stages of insects
with complete metamorphosis usually
quite different in form
Holometabolis
• Often live in very different habitats
and
• Have different feeding preferences
Holometabolis
• Larvae do not have compound eyes
• May or may not have thoracic legs
• Wing development arrested
Holometabolis
• How do these structures develop in
adults?
• Discs of undifferentiated cells
• Discs grow, but remain undifferentiated
Holometabolis
• After molt of last larval instar, insect
changes into form called pupa
–
–
–
–
–
nonfeeding stage
very active metabolically
inactive physically
covered by cocoon or other protective
material
Diapause
•
•
•
•
State of arrested development
Widespread phenomenon
Unstable environment
Common in biomes with extremes for
long periods
Diapause
• Examples exist across all stages
• Requires stimulus to initiate and end
• Usually preceded by accumulation of
resources
Diapause
• Univoltine = one generation per year
• Bivoltine = two generations per year
• Multivoltine = more then two
Diapause
• Univoltine = obligate diapause
• Bi- or multi-voltine = facultative (reared
continuously)