Insect Dissection Lab (III)

Name:______________________
Insect Dissection Lab (Part 3)
Insect Physiology (Ento 306)
Introduction: Like the two previous labs, this handout provides you with the basic instructions
for dissection and an outline of the tissues, organs, and structures that you will need to be
familiar with and draw. All questions you need to ask or things you need to draw are
underlined. Attached is a sheet of circles in which you will make all your drawings which must
include a short description and magnification used. Draw the structures as accurately as
possible but don’t worry; you’re being graded on accuracy and participation, not artistic ability.
Make use of the appendix which is a collection of diagrams from the textbook and literature
that will be helpful in finding the correct structures and organs.
Supplies:
-­‐ Saline Solution
-­‐ Dissection probes
-­‐ Forceps
-­‐ Scissors
-­‐ Razor blade
-­‐ Insect/dissection pins
-­‐ Dissection pan
-­‐ Stereoscopic dissecting microscope
-­‐ Compound microscope
-­‐ Microscope slide and coverslip
-­‐ Freshly sacrificed organism:
-­‐ South American cockroach (Blaberus sp.)
-­‐ Tobacco/Tomato hornworm (Manduca sexta)
-­‐ Tobacco budworm (Heliothis virescens)

Dissection of cockroach nervous system
Ventral nerve cord and ganglia
Insect Physiology (Ento 306)
Remove the wings by cutting their attachments with a pair of scissors. The dissection is
facilitated if the legs are removed by cutting across their trochanters. Insert the blade of a pair
of fine scissors in the lateral margin of the body between the tergite and sternite. Insert the
blade only as deep as is necessary to penetrate the exoskeleton and be careful you do not
damage internal organs with deep cuts. Cut anteriorly along the right side of the tergites all the
way to the anterior end of the pronotum. Cut transversely across the anterior margin of the
pronotum, just posterior to the head, and upon reaching the left side, change directions and cut
posteriorly along the left side all the way back to the last tergite. Make a transverse cut through
the exoskeleton across the posterior border of the last tergite. You have now cut all of the way
around the dorsum.
Remove the dorsal diaphragm along with the tergal muscles, tracheae, and heart from the
abdomen. Accomplish this by cutting with fine scissors around the periphery of the abdomen.
Remove the gut, fat body, reproductive organs from the thorax and abdomen. Remove the
longitudinal body wall muscles (sternal muscles) and connective tissue as necessary from the
floor of the abdominal cavity to reveal the ventral nerve cord.
Identify and draw one of the three thoracic ganglia. From each extend several pairs of nerves to
the abundant muscles of these segments.
Cockroach brain
Using your scissors and forceps or a razor blade carefully remove the epicranium (top of the
head) from the region between the compound eyes and antennae. Remove muscles as
necessary to reveal the bright white, dorsal brain between the compound eyes.
Draw the cockroach brain in as much detail as possible. Label at least two of the following
features:
-­‐ Optic lobe
-­‐ Protocerebrum
-­‐ Deutocerebrum
-­‐ Tritocerebrum
-­‐ Corpora cardiac
-­‐ Corpora allata
-­‐ Circumesophogeal connective

Dissection of Tobacco hornworm caterpillar
External features
Insect Physiology (Ento 306)
Manipulate the caterpillar so you are able to draw it in an en face position. Draw what you see
and label the following features using the stereo dissecting microscope:
-­‐ Labrum
-­‐ Mandibles
-­‐ Maxilla/maxillary palp
-­‐ Spinneret (for producing silk)
-­‐ Antennae
-­‐ Ommatidia
-­‐ Legs
Identify the following structures involved in walking on the caterpillar
-­‐ Proleg
-­‐ Anal proleg/Anal clasper
Identify and draw a spiracle
Caterpillar hemocoel dissection
Cut off the caudal horn at its base. Insert scissors into the hole from the cut-­‐off horn and cut
through skin and body muscle along a line down the center of the caterpillar’s dorsal side. Cut
from caudal to rostral (head) end. Pull open the exoskeleton and use dissection pins to hold the
exoskeleton and body muscles open by pinning through the body wall at an outward angle.
Bathe the caterpillar in saline solution.
Identify the gastrointestinal tract, fat body, and trachea.
Gastro-­‐intestinal tract
Use forceps to tear the esophagus and lift out the digestive track carefully.
Identify the following features
-­‐ Crop/midgut
-­‐ Malphigian tubules
-­‐ Proctodeal valve
-­‐ Intestine
-­‐ Rectum

Insect Physiology (Ento 306)
Note that the malphigian tubule tips are attached to the rectum. This is termed the crypto-­‐
nephridial arrangement.
Estimate what % of the caterpillar body cavity is made up of the caterpillar gut
________% of body cavity
Nervous system
Locate the caterpillar’s ventral nerve cord. Identify the abdominal and thoracic ganglia.
Draw the entire dissected caterpillar under low magnification highlighting the nerve cord and
label the ganglia. Do not include the gastrointestinal tract, trachea, or fatbody.
Tease or cut open the caterpillar’s head capsule and locate the brain.
Dissection of the Tobacco budworm moth
External features
Draw the moth’s head and label the following features:
-­‐ Labial palps
-­‐ Proboscis
-­‐ Compound eyes
-­‐ Antennae
Moth hemocoel cross section
Cut off the moth’s wings and lay it ventral side up in the dissection pan. Using a razor blade cut
through the moth sagitally. Lay the two halves on their side and use a probe or forceps to
spread open the abdomen. Identify the flight muscles, trachea reproductive organs (include the
male ‘hair pencil’ or female ovarioles), and if possible the gastrointestinal tract. Draw the
moth’s internal anatomy in cross section labeling the flight muscle and reproductive organs.
Estimate what percentage of the body cavity these two sets of tissues occupy.
__________%
Think about the generalized anatomy of a grasshopper or cockroach compared to that of
the caterpillar and moth. What does this say about the behavioral ‘priorities’ of these
different organisms?

Dissection illustration sheets
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Insect Physiology (Ento 306)

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Insect Physiology (Ento 306)

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Insect Physiology (Ento 306)

APPENDIX
Anterior view of the head of Periplaneta fuliginosa
Illustrations by Richard Fox http://webs.lander.edu/rsfox/invertebrates/periplaneta.html
Insect Physiology (Ento 306)
Dorsal view of the perivisceral coelom of a male P. americana. The dorsal diaphragm,
heart, and tergal muscles have been removed. Abdominal segments are numbered.
Malpighian tubules have been shortened and reduced in number for clarity.
Illustrations by Richard Fox http://webs.lander.edu/rsfox/invertebrates/periplaneta.html

Insect Physiology (Ento 306)
Dissection of P. americana showing nervous system. T = thoracic ganglion, A =
abdominal ganglion. The abdominal segments are numbered.
Generalized insect brain in lateral view.

Insect Physiology (Ento 306)
Diagrammatic cross section of a generalized insect abdominal segment. Redrawn from
Snodgrass (1935)
Illustrations by Richard Fox (http://webs.lander.edu/rsfox/invertebrates/romalea.html)
External anatomy of a generalized caterpillar. Redrawn and modified from Snodgrass
(1935).
Illustrations by Richard Fox (http://webs.lander.edu/rsfox/invertebrates/papilio.html)

Insect Physiology (Ento 306)
Dorsal view of the head capsule of the larvae of Papilio polyxenes. Anterior is at the top.
Internal anatomy of a generalized caterpillar viewed from the left. Two of the three left
Malpighian tubules have been truncated for clarity. Redrawn and modified from
Snodgrass (1935).

Lepidopteran mouthparts
Internal anatomy of an adult and larval lepidopteran.
Insect Physiology (Ento 306)