Practical No 5- Observation of Phototaxis in Insect Larvae

 Practical No 5- Observation of Phototaxis in Insect Larvae

Phototaxis refers to the movement of organisms in response to light. Organisms can exhibit positive phototaxis (movement towards light) or negative phototaxis (movement away from light).

 Aim: To observe and document the phototaxis behavior of insect larvae in response to light.

Equipment Needed

1. Insect Larvae: Commonly used species like fruit fly larvae or mealworm larvae.
2. Light Source: A lamp or flashlight to provide a consistent light source.
3. Dark Chamber or Box: To create a controlled environment with a gradient of light intensity.
4. Petri Dishes or Transparent Containers: To house the larvae during the experiment.
5. Graph Paper: To document movements.
6. Timer or Stopwatch: To record the duration of observations.
7. Notebook and Pen: To record observations and results.

Procedure

1. Preparation:
• Choose healthy insect larvae for the experiment.
• Prepare a dark chamber or box with a light source at one end to create a gradient of light intensity.
• Place the larvae in the center of the Petri dishes or transparent containers within the dark chamber.
• Turn on the light source at one end of the chamber to create a light gradient.
2. Observation:
• Mark the initial position of each larva.
• Note the direction and distance moved by each larva towards or away from the light source over a fixed period (e.g., 10 minutes).
• Observe any specific behaviors or patterns, such as rapid movement, turning, or pausing.
• Repeat the observations multiple times to ensure consistent results.
• Introduce variations, such as changing the intensity of the light source or using different wavelengths (colors) of light, to see how the larvae respond.
• Calculate the average distance moved and the percentage of larvae exhibiting positive or negative phototaxis.

• Direction of Movement:
• Positive Phototaxis: (Move toward the source of light)
• Negative Phototaxis: (away from the light source)
• Distance Moved: Note the distance and time  
• Behavioral Patterns: Example: Larvae exhibited rapid, straight-line movements towards the light source or away from the source)

 

Results:                1. ------ % of the larvae showed positive phototaxis moving towards the sight source.

2. ------ % of the larvae showed negative phototaxis moving towards the sight source.

3.  The average distance moved towards the light source was -------  cm, while the average distance moved away from the light source was -- ---- cm.

Conclusion:  The experiment showed that most insect larvae move towards light, indicating positive phototaxis, likely to find better living conditions or food sources.

 

(Note: Ensure that the larvae are handled carefully and returned to their habitat after the experiment. Avoid exposing the larvae to prolonged stressful conditions.)