Cricket Dissection

Charlotte St. Romain
1991 Woodrow Wilson Biology Institute

Objective:

To provide an easy animal dissection. To provide a simple system to test the effects of various chemicals on breathing and heartbeat rate.

Background:

There is much controversy about vertebrate animal dissection fueled by animal rights groups but many students learn a great deal by dissecting and look forward to the activity. Some students need the 3 dimensional model to distinguish the morphological features and to understand how the systems are integrated and work. We selected house crickets because they are readily available, easy to rear and maintain, inexpensive, reproduce in large number, and they are not generally distasteful to most people.

Materials:

for group of 2 students:

2 house crickets
dissection pan (or wax-filled Petri dish)
source of CO2
forceps
scissors
pins
dissecting microscope
Insect Ringer's solution (see appendix for recipe)
solutions for neurotransmitters

Procedure:

Note the 3 body regions: the head - 5 segments, the thorax - 3 segments, and the abdomen - 10 segments. The wings and legs are located on the thorax. Remove the wings and legs and put the insect abdomen (ventral) side up in the dish.

Pin the insect to the wax by placing 1 pin through the head and another through the base of the abdomen. Caution! Be sure the pin in the base is placed way off the midline. The heart is in the midline lying just beneath the cuticle on the dorsal side of the insect. Although the tube heart is quite sturdy, pinning may cause damage to the structure.

With sharp-pointed scissors, make two longitudinal incisions along the side of the cricket's cuticle. Make the incisions from the base of the abdomen to the top of the abdomen. Once the abdomen is open be sure to cover it with insect saline so that the heart does not dry out. Carefully, cut across the cuticle between these two cuts at the top of the abdomen and cut the flap off. You will now be able to see yellow malphigian tubules which will be actively moving about the body cavity. Observe their movement, then carefully lift them and cut them out.

The female is distinguished from the male by the ovipositor or egg layer. The male has different shaped wings. If it is a female, remove the ovaries/oviducts before you try to see anything else. Sometimes the ovary is broken and many eggs are released into the body cavity. The eggs are whitish capsules which can obscure and compress all the other organs. The eggs can be removed by simply washing the body cavity with saline solution.

The force necessary for moving blood through the organism is provided by musculature associated with the major tube of the circulatory system. In open systems, muscle provides the force to move blood or fluid back into the major tube, which is referred to as the heart, for redistribution to the body. Such hearts in insects contain ostia which are opened by alary muscles creating the force for fluid movement into the heart. Sequential alary muscles beat such that a wave-like contraction is observed along the heart. The movement of this "peristaltic" wave is from the tail of the insect toward the head. Determine the respiratory rate which generally ranges from about 10 to 20 abdominal contractions per minute, and the heart rate which generally ranges from about 90 to 120 beats per minute. The heart is a thin, almost transparent tube visible through the intersegmental membranes along the mid-dorsal region.

With the alimentary tract in place note the peristaltic movements, the coiling of the hind gut, and the connections of the tracheae. Grasp the esophagus with a forceps and cut just anterior to that point. Slowly lift the anterior end of the alimentary canal, carefully cutting the tracheal connections until only the rectum is connected.

Analysis:

At which end of the heart does the contraction appear to begin?
Is the strength of the beat uniform along the length of the heart?
What is the respiratory rate?
What is the heart beat rate?

Optional experiment:

It is now possible to test the effects of neurotransmitters in insects. The 3 chemicals we will test are octopamine, serotonin, and glutamate. Start with a small concentration of the test solution to determine when a physiological response occurs. Some responses to look for include increases in heartbeat and respiration. Which of these chemicals has the greatest effect? Does the chemical increase or decrease the heart rate? Are there other substances that would be of interest for testing purposes? Give some reasons for your choice.

References

Dini, M. and Harris, J. (1991). "Cricket Heart Activity - Response to Neurotransmitters." Aninal Physiology Update Workshop Manual. LSU, Baton Rouge.

Wodring, Joseph, "Internal-external morphology of the house cricket." LSU, Baton Rouge.

Appendix

Insect saline:: NaCl 9.1 g/L, KCl 0.52 g/L, CaCl2 . 2 H 2O, 1.2 g/L MgCl2 . 6 H2O .8 g/L
Neurotransmitters:: Octopamine Cl: 1.89 mg/100 ml saline; Glutamate Na 1.87 mg/100 ml saline; Serotonin HCl: .213 mg/ml saline

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