Saddleback Journal of Biology - Saddleback College

Fall 2009 Biology 3B Paper
provide an optimal environment to begin ecdysis to an
adult stage than a temperature slightly lower.
Metamorphosis should progress at a faster rate at a
higher temperature if the hypothesis is supported.
Materials and Methods
To collect data for this experiment,
investigators recorded the amount of days it took for
each V. cardui caterpillar to begin its pupa stage from
the day it began its larval stage, or the day it hatched.
There were many variables that needed to be accounted
for to ensure the least variability in the subjects such as
age, type and amount of food source provided, living
habitats, and daily photoperiods. Thus, all larva
hatched on the same day, all were provided with an
equal amount of artificial diet that filled the bottom of
their habitat to ensure they could each eat as much as
they need, all resided in plastic rearing cups provided
by Mulberry Farms, and both variable groups had a
photoperiod imitated by a lamp providing 12 hours of
light and 12 hours of darkness in each incubator. This
light pattern mocks a typical day during the summer
season, when V. cardui are most abundant. The
variable being tested was temperature: one group of
larva was placed in an incubator at 72F, or 22.2C,
and another at 82F, or 27.7C. Both incubators used
were in the Saddleback Student Research Laboratory.
Sixty-one larvae were obtained for this study;
however, only the larvae that survived to progress into
the pupa stage were included in the sample size. In the
test group incubated at a higher temperature, out of the
original 33 larvae, 20 were included in the sample size.
Likewise, for the other test group, out of the original 28
larvae, 24 were included. Overall, 72% of the
originally obtained larva survived to become a
chrysalis. The larva were 3 days old when individually
transferred and separated from a single large Petri dish
into 5 rearing containers, each with approximately 10-
15 larva. Three of the containers were placed in an
incubator set at 27.7C with a lamp on a 12-hour on
and 12-hour off timer, while the other two were placed
in an incubator set at 22.2C with a similar lamp setup.
The caterpillars were observed daily and the
investigators recorded the day each larva began
pupation. From the raw data, the number of days it
took each caterpillar to reach the pupa stage from
hatching was calculated.
All data were transferred to MS Excel
(Microsoft Corporation, Redmond, Washington) where
further analysis took place. To analyze the data
collected, investigators calculated the mean number of
days it took each caterpillar to proceed from larva to
pupa stages for each of the two temperature groups.
Using an unpaired, one-tailed t-test, statistical analysis
was performed, which provided the p-value needed to
either reject or support the null hypothesis. In addition,
a chi-squared test was performed to justify the validity
of our results.
Results
Upon viewing the specimens, the chrysalis
size of the groups placed in the higher temperature of
27.7°C were significantly larger than those placed in
the lower temperature. The specimens in sample
groups of the V. cardui incubated at 27.7 °C cocooned
after a mean time of 11.45 days, while the mean time
for subjects incubated at 22.2°C was 15.57 days. To
determine if differing temperatures affected the rate of
metamorphosis, a one-tailed t-test assuming unequal
variances was completed. The null hypothesis that the
temperature of incubation provides no significant input
in the rate of metamorphosis can be rejected (p