How Does Lighting Affect the Time it Takes for a Caterpillar (Vanessa Cardui)
to Turn Into a Chrysalis?
Matthew Crespo, Marcos Delgado, Cashai Fountain, Bernard Kleiman
Rosana Josepha, Patrick Martin, Megan Morales, Katherine Sanchez
Introduction
The Painted Lady butterfly is a pollinator found in many places in North America. Their larvae
(caterpillars) eat plants in the daisy family and the hibiscus family. The butterflies live in places
where day length is different. We wonder if caterpillars grow at different rates if they have less
daylight, which would mean butterfly populations might grow more slowly in northern parts of their
range.
The purpose of this experiment is to see if Vanessa cardui caterpillars grow faster in complete
darkness or in a normal night/day cycle. Our resuilts could help other people grow the caterpillars
faster. It would also help other scientist grow their caterpillars best for their experiments. They
start off as a caterpillar then they form a chrysalis. After they form a chrysalis they turn into a
butterfly. We predict that by putting the caterpillars in total darkness they would form a chrysalis
slower than if they have a normal day/night cycle. The darkness will cause them to grow slower
because it messes up their circadian rhythm.
H0: The caterpillars in the dark will form a chrysalis at the same rate as the ones in the light.
H1: The caterpillars in the dark will form a chrysalis at a different rate as the ones in the light.
Materials
* 2 lamps
* Scale
* 2 Thermometers
* 20 caterpillars
* 2 boxes (one for control, one for treatment)
* 20 cups
* Caterpillar food (7 ozs)
Methods
Caterpillars were housed in small plastic cups, one per cup. Each caterpillar got 7.5 grams of
commercial caterpillar food. Ten cups were placed in a bin in a dark box (fume hood) with a heat
lamp (covered). Ten cups were placed in the fume hood with a light source on a timer (12 hours of
light, 12 hours of dark), and a heat lamp (covered). We recorded the days to pupation for each
larva.
Results
We started out with 10 caterpillars in the control group but we ended out finishing 8 that did
pupate. One died and one had not pupated by the time we ended our experiment. For our treatment
group we also started out with 10 caterpillars in the treatment and ended with 8 caterpillars. The
other two died. There was no difference in the days to pupation between the treatment and control
groups. Our t-statistic was 1 (degrees of freedom =1), which had a P value of > 0.05. This means
we cannot reject our null hypothesis. There was no difference in the rate of pupation between the
fully dark and light/dark caterpillars. You can see this in Table 1.
Discussion
We observed that most of the caterpillars started to pupate faster in an all dark cycle rather than the
one in the normal night/day cycle. However, this difference was not significant when we did the ttest. We think the caterpillars did not like the dark environment, and tried to pupate faster so they
could fly away and find light. We would have to do this experiment again with more caterpillars to
see if we can get the same results.
Table 1. Days to pupation for caterpillars housed in fully dark (treatment) and light/dark
cycle (control) habitats.