The effect of light on the Vanessa cardui By Michael Muransky The subject of this experiment is painted ladies caterpillars. Their eggs are pale green and are placed on the upper- side of the leaves. They have a yellow stripe down their back and many spines along each side. This species is extremely common and the only place they don t is Antarctica and some remote islands. They can live almost anywhere, but they prefer brightly lit and covered environments. Females lay eggs on the plants their babies will eat. The caterpillars that hatch out feed continuously and molt several times. After a few weeks they transform into a pupa, go through a complete metamorphosis, and emerge as an adult butterfly. The timing of this depends on the climate, the warmer the climate the faster they grow. They rarely live for more than one winter, and reproduce in the summer, but it may go on year- round in warmer climates. The problem in this experiment is whether caterpillars grow better in complete darkness or in complete light. We would want to study this problem because if caterpillars grow better in complete light, then we know that maybe humans grow better in complete light. We now may assume that humans grow healthier in places like Florida where it is light almost year round. What I knew about this subject before I studied it was that caterpillars form cocoons before they develop into a butterfly. I also knew that they feed on leaves. My hypothesis was that these painted lady caterpillars will grow better in total lightness. I believe in my hypothesis because they can observe more nutrients from the light such as Vitamin C. Also, in previous experiments scientist state those painted lady caterpillars grow better in brightly lit environments. We will test this experiment by placing 2 containers in a fume hood and placing a lamp covering the control group. We set up a divider separating the control group and the treatment group and keeping the control group in total darkness. However, this divider allows heat to pass through so temperature remains constant. Every morning, we will observe the caterpillars and record whether they are alive or not.
Photo Credits to butterflyireland.com Photo credits to entomology.edu
Materials and Methods Materials: 1) 30 small cups. We will use this to hold the caterpillars and their food. We are using cups because this will allow us to manipulate the cups to record whether the caterpillars are alive or not. We will place 1 caterpillar per cup. 2) 300 grams of painted lady caterpillar food. We will put about 10 grams of food per cup. We will use this to feed the caterpillars. 3) 1 Divider. This will allow heat to pass through, yet will prevent light from passing through to the control group. 4) 1 Thermometer. This will help us record the temperature. 5) 1 fume hood to hold the caterpillars and let them grow in peace. 6) We need 30 painted lady caterpillars. We used 15 for control, and 15 for treatment. Methods: 1) First we placed 1 caterpillar per cup with 10 grams of food. 2) Next we placed 15 caterpillars under light at 20 C, and another 15 in total darkness at 20 C. 3) Every day we measured whether or not the caterpillars are alive, and the temperature. 4) When the caterpillars remaining have all pupated we will release them.
Results: This bar graph shows the days it took the caterpillars to pupate. C represents the control group, and the number next to it represents the caterpillar number. E represents the experimental group, and the number next to it represents the caterpillar number. As you can see the control group pupated faster than the experimental. The mean for the number of days to pupate for the control group is 21 days. The mean number of days to pupate for the experimental group is 22 days. The variance for the control group is 1.4, and the variance for the experimental is 0.5. These numbers are very small so this shows the numbers aren t very far from the mean Discussion: Given the results we are pretty surprised because we thought the treatment group would live longer and pupate faster than the control group. However, the contrary occurred. The control group lived longer and pupated faster. The T-Test value was 0.017314 and that was less than 0.05 so we will reject the null hypothesis, and fail to reject the alternative hypothesis. The potential sources for mistakes are when we were checking on the caterpillars we opened the fume hood and maybe they were exposed to just the right amounts of light. We think the next step in the experiment would be to present our results and maybe investigate further. We would
investigate further by replicating the experiment and if they grow better in darkness still, then we would view whether humans grow better in dark or light. However, if this does not work we could observe which amounts of light caterpillars grow best in. Bibliography: http://www.biokids.umich.edu/critters/vanessa_cardui/ University of Michigan Painted lady butterfly Vanessa cardui July 16, 2013