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Amazing Monarch Larvae - Does Heat or Light Affect the Direction of the Pre-Pupal "J"?

Brad Larson and Sopaula Nou
Willow Creek Middle School
Rochester, MN

Brad and Sopaula with their insect fair project display (Photo: Brad Larson and Sopaula Nou)

Abstract

We used 8 copy paper boxes with 8 plastic tubs inside them. Four boxes had 4-inch square holes cut in one end and the other 4 boxes had no openings. We put the boxes 10 inches away from a 40-watt light bulb in a north, south, east, and west orientation. We put seven 5th instar monarch larvae in each of the tubs and then put the tubs into the boxes. In the boxes with openings exposed to the light, the larvae always "J"ed away from the light, regardless of the direction of the opening. The larvae in the closed boxes "J"ed in many different directions. We are uncertain if there are other factors that determine the direction of the "J". We learned that monarchs pupate with their backs to the light. It is probably less annoying...like sleeping with the lights off instead of having them shine in your face!

Observation

We noticed that monarch larva made their chrysalides in many different directions. We wondered why some hang in some directions while others, right next to it, hang in different directions.

Question

Does light or heat affect the direction of the pre-pupal "J"?

Hypotheses

  • The direction of the "J" is random.
  • They will "J" towards the light.
  • Males will "J" one way, while females will "J" another way.

Experiment

Materials

  • 8 identical copy paper boxes, four with identical 3 x 4 openings and four without
  • 8 identical clean plastic tubs
  • light / heat source - 40 watts
  • textbooks to place under boxes so all were level at the same time
  • 5th instar larvae - 7 per box
  • enough food for larvae

Procedure

Step One - Gather all your materials

Step Two - Prepare boxes in the following way:

  • cut a 4-inch hole in the center of the end piece on 4 boxes
  • put 25 milkweed leaves in each tub
  • place larvae in the boxes

Step Three -

  • Position the boxes so that all the boxes are 10 inches from light.
  • Each end with a hole should face in a different direction: 1 north, 1 south, 1 east, and 1 west.
  • Repeat the same thing using the boxes without holes (to assure the effect of heat only).

Daily - Remove tubs keeping N/S/E/W orientation constant. Feed larvae as needed (fresh food daily) until pupated.

Analyze Data / Results

All of the larvae in the light experiment pupated with their backs to the light regardless of the light's direction (from the north, south, east, or west). Some were closer to the light and others were farther away, but in each tub they were all facing the same direction. We thought that might be a response to the heat generated by the light, so we repeated the experiment with boxes that had no light shining through. The larvae in closed boxes pupated in random directions.

Conclusion

The larvae that we raised in the tubs with light shining on them always "J"ed away from the light and the larvae who only had heat "J"ed in all directions. The conclusion of this experiment is that larvae pupate away from light and that heat doesn't affect the direction of their "J".

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