Int 256 – Tree Pests and Disease Laboratory #2: Page 1
INT 256 - Laboratory #2
Insect Morphology and Development
(Edmonds p. 418-426)
I.
Purpose:
A.
Recognize and understand purpose of primary structures and systems in insects.
B.
Compare and contrast two kinds of metamorphosis in insects
II.
Materials:
Dissecting microscope or hand lens, grasshoppers, insect specimens embedded in
glass, dissecting scissors, glass plates, dissecting probes, forceps, nitrile gloves,
safety glasses.
Safety Note: Grasshoppers are preserved in a solution of propylene glycol, a
relatively non-toxic compound. However, to avoid any possible irritations, please
use the following precautions:
III.
A.
Avoid all contact with skin and cloths.
B.
Use safety glasses (please return) and nitrile gloves (disposable).
C.
Dispose of all insect parts in the plastic bag at the front of the room.
Grasshopper Dissection
A.
B.
Introduction
1.
Put on safety glasses and nitrile gloves
2.
Place a grasshopper into a petri dish using forceps.
3.
Return to your table.
4.
Also refer to pages 418-424 in the textbook and the diagrams.
External structure: Examine, sketch, and label the three regions of the insect
body including all of the following:
1.
2.
Head
a)
Compound eyes
b)
Simple eyes
c)
Antennae
d)
Mouth parts
(i)
2 mandibles
(ii)
2 pairs of maxillae
Thorax: 3 segments, 1 pair of legs/segment
a)
Prothorax
b)
Mesothorax - 1 pair of wings
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3.
C.
D.
c)
Metathorax - 1 pair of wings
d)
Function: locomotion
Abdomen
a)
Sketch if male or female
b)
Find spiracles
Exoskeleton:
1.
The hard covering of the insect is made of chitin.
2.
An epicuticle of wax and oils covers the entire surface to prevent water loss.
3.
Protects internal organs and is where muscles are attached so that movement is
possible.
4.
The exoskeleton is varies based on the thinkness of various exoskeletal layers.
Identify and label a location on the grasshopper that indicates the
following types of exoskeleton
a)
Exocuticle is thick – very hard and strong
b)
Endocuticle is prominent – tough but flexible
c)
Only membranes present – flexible and weak
Internal Structure
1.
Cut open the insect.
a)
Place in glass dish
b)
Use the scissors and forceps to remove the legs
c)
Starting at the head, use the scissors to cut the exoskeleton down each
side of the insect, just above (dorsal side) of the leg joints
d)
Use the forceps and scissors to remove the ventral part of the exoskeleton
e)
Note and sketch a portion of the tracheal tubes running from the
spiracles to the organs
f)
(i)
How gas exchange occurs in insects
(ii)
Used instead of lungs
Carefully remove the any fatty tissue that covers the internal organs
(i)
E.
IV.
Sketch and label parts of the digestive system: Crop, gizzard,
stomach, intestine
When complete, have the instructor check your sketches before disposing of the
insect.
Insect Growth and Development
A.
Molting
1.
Mechanism
a)
Each growth stage larger than previous
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2.
B.
C.
b)
Dissolve endocuticle and some exocuticle - then shell
c)
Epidermal cells secrete new cuticle - must have folds to fit inside old
cuticle
d)
Emerge from old cuticle
e)
Expand new cuticle by taking air
f)
Harden new cuticle by secreting sclerotin
Vulnerability
a)
Without sclerotin, cuticle can be easily penetrated
b)
Predators, cannibalism, fungi
Developmental stages
1.
Egg
2.
Immature stages - instars
3.
Adults
Types of development
1.
2.
Ametabolous insects - no metamorphosis
a)
Example: Grasshopper
b)
6 instars then adult
c)
Note and sketch development changes
(i)
Early stage (#4)
(ii)
Final stage
(iii)
What are the major differences?
Holometabolous insects a)
Complete metamorphosis
b)
Has pupal stage
c)
Example: Silkworm Moth
d)
Note and sketch each development stage:
(i)
Eggs - embryo development
(ii)
Larvae - feeding and growing
(iii)
Pupae - metamorphosis into different life form (adult)
Adults - reproduction and dispersal
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V.
Terminology.
FTY 100 - Lecture : page
A.
Terms
abdomen
adults
ametabolous
chitin
crop
cuticle
digestive system
egg
endocuticle
epicuticle
exocuticle
exoskeleton
gizzard
head
holometabolous
instars
intestine
larval
membranes
mesothorax
metamorphosis
metthorax
molting
nymphal
prothorax
pupal
sclerotin
spiracles
stomach
thorax
tracheal system
2