THE EFFECTS OF TEMPERATURE ON GROWTH IN VANESSA CARDUI
LARVAE
Lorena Cordova and Michael McLaughlin
Department of Biological Sciences
Saddleback College
Mission Viejo, CA, 92692
The experiment was conducted to determine if there was an increase or decrease in
growth length at difference temperatures in the Painted Lady larva, Vanessa cardui.
Larvae were exposed to low, medium (room temperature) and high temperatures.
The larvae were separated into three groups of ten and placed into three separate
incubators at 16ºC, 22ºC, and 28ºC. The length of each caterpillar was measured
every other day for a total of seven days. It was hypothesized that larvae in the
warmest incubator would have greater growth than larvae in the coolest incubator.
No significant difference was found for the growth length of larvae between the
16ºC and 22ºC incubators (p>0.05, one-tailed ANOVA). There was also no statistical
difference between the control (22ºC) and higher (28º) incubation temperatures
(p>0.05, one-tailed ANOVA). Using a Post Hoc test, a significant difference was
found between the growth of larvae at the low temperature of 16ºC and the high
temperature of 28ºC (p<0.05, one-tailed). The null hypothesis was rejected from this
study. The difference in growth may have been due to the altered metabolic rates of
the larvae, which may have been affected by the varying environmental
temperatures.
Introduction
There are certain species of butterflies that live in the northern regions of America.
When temperatures decrease and winter approaches, the butterflies migrate south towards
Florida and Mexico (Bryant, 1977). There is a general trend between butterflies and the
ambient temperature. As climate temperature increases, butterfly populations likewise
increases (Pollard, 1998). A change of climate temperature by an order of 3°C can result
in an increase of butterfly populations as soon as two to three weeks. The trend suggests
an overall preference towards warm temperatures.
Although, many factors affect larval growth, temperature and food quality are
among the greatest to impact growth rates, consumption rates, utilization efficiencies, and
developmental time in many herbivorous insects (Levesque et al., 2002). Not surprisingly,
the growth rate and diet in larval state strongly depend upon daytime temperature (Stamp
and Bowers, 1990). Larvae living in environments with a temperature of 18°C or lower
have shown stunted growth rates compared to larvae in warmer temperatures such as
24°C and 30°C. The duration of the instar stage of metamorphosis can decrease
significantly with increasing temperatures (Levesque et al., 2002). As data would suggest,
rates of metamorphosis should increase as the environmental temperature increases.
However, there is a limiting relationship between maximum temperature and
maximum growth rate. As temperatures increase towards 37°C, larvae are observed to
have suppressed mass accumulation rates and poor survivability (Scriber and Lederhouse,
1983). Growth and consumption rates of caterpillars increase between 14°C and 26°C,
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reach a maximum at 34°C, and quickly decline above 38°C (Kingsolver and Woods,
1997).
This study will look into the effects of temperature on the growth of Painted
Lady, Vanessa cardui, larvae. Previous research indicates a preference towards warmer
temperature in larvae which results in an increased growth rate, and consequently, a
reduced metamorphosis time span. It is hypothesized that larvae placed in a warm 30°C
environment will yield significantly larger growth lengths than larvae living in a cool
16°C environment.
Materials and Methods
In order to observe the differences in growth of larvae, data was recorded over the
span of seven days. Thirty Painted Lady larvae were purchased from Chase'N
Butterflies© and used in this study. The study took place at Saddleback College in
Mission Viejo, CA. Ten larvae were placed in three separate plastic containers of equal
size with equal amounts of food. Initial lengths were recorded, in millimeters, of each
larva using a caliper. The three containers, each containing ten larvae, were then placed
in separate incubators with settings of 16ºC, 22ºC and 28ºC. The incubator set at 22ºC
served as the control group.
The lengths of each larva was measured every other day (day 1, day 3, day 5 and
day 7) up until the first cocoon was observed (day 10), which was in the 28ºC incubator.
All raw data was transferred to MS Excel (Microsoft Corporation, Redmond, Washington)
and analyzed. Growth difference was calculated by subtracting the final lengths of each
larva on day seven by the initial lengths of each larva on day one. A one-tailed ANOVA
was used to analyze growth differences in the three incubation temperatures. Further Post
Hoc testing was used to determine where the statistical difference lied within the groups.
Average mean length at each temperature for all days recorded was calculated
separately. A general trend line was then produced using this data for the three incubation
temperatures.
Results
On day one, the average length of the caterpillars was 9.7 mm ± 1.2 (± SEM,
n=10) in the 16°C incubator, 10.2 mm ± 1.1 (± SEM, n=10) in the 22°C incubator, and
10.6 mm ± 1.9 (± SEM, n=10) in the 28°C incubator.
Measurements of the average length of the caterpillars on day three was 10.9 mm
± 1.0 (± SEM, n=10) in the 16°C incubator, 10.7 mm ± 1.3 (± SEM, n=10) in the 22°C
incubator and 11.9 mm ± 1.8 (± SEM, n=10) in the 28°C incubator.
Day five results yielded the average length of caterpillars of 11.3 mm ± 1.2 (±
SEM, n=10) in the 16°C incubator, 12.7 mm ± 1.3 (± SEM, n=10) in the 22°C incubator,
and 15.1 mm ± 2.2 (± SEM, n=10) in the 28°C incubator.
The measurements of day seven resulted with an average length of the caterpillars
of 12.6 mm ± 1.1 (± SEM, n=10) in the 16°C incubator, 14.5 mm ± 2.0 (± SEM, n=10) in
the 22°C incubator, and 16.6 mm ± 2.3 (± SEM, n=10) in the 28°C incubator. The means
created a general trend of increase for all three incubation temperatures.
The general trend was graphed between all three incubation temperatures using
the average lengths for each day observed (Figure 1).
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18
16
Average Length (mm)
14
12
10
8
6
4
2
0
Day 1
Day 3
16°C
Day 5
22°C
Day 7
28°C
Figure 1. General trend of V. cardui larvae at 16°C, 22°C and 28°C. Larvae in the
highest temperature of 28ºC have the largest final length measurements.
The ANOVA revealed a statistical difference between caterpillar growth in the
three incubation temperatures (p= 0.014, one-tailed ANOVA). Further Post Hoc testing
showed no statistical difference between growth in the 16°C and 22°C incubators
(p>0.05). There was also no significant difference between growth in the 22°C and 28°C
incubators (p>0.05). However, there was a statistical difference between the 16°C and
28°C incubators (p<0.05) (Figure 2).
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9
Average Growth Difference (mm)
8
7
6
5
4
3
2
1
0
16°C
1
22°C
28°C
Figure 2. There was no statistical difference in growth between caterpillars in the 16°C
and 22°C incubators nor the 22°C and 28°C incubators (p>0.05, one-tailed Post Hoc test).
There was a statistical difference in growth between the caterpillars in the 16°C and 28°C
incubators (p<0.05, one-tailed Post Hoc test). Error bars represent mean ± SEM.
Discussion
The 16°C and 22°C incubation temperatures had no statistical difference between
growth rate of the larvae (p>0.05). The same holds true for larvae between 22°C and
28°C incubation temperatures (p>0.05). This is most likely due to the negligible
differences in the temperatures. While the trend lines show the control group with greater
growth lengths than the 16°C group, the data was not enough to be considered
statistically different. There was, however, a statistical difference found between growth
in the two extreme temperatures, 16°C and 28°C (p<0.05). The hypothesis for this study
was accepted and the null hypothesis was rejected.
The results support that warmer temperatures are more ideal for larval growth
than cooler temperatures. Two cocoons were present in the 28°C incubator on the tenth
day of this study. These cocoons were further observed to have completed
metamorphosis and emerged as butterflies within four days. The average metamorphosis
length of the common butterfly larvae lasts approximately seven to ten days (Pelling et
al., 2008). Based on past research and the findings in this study, metamorphosis rates
appear to increase when larvae are in warmer temperatures.
A possible explanation for the increased growth in warmer temperature may be
found in the metabolic rates of the larvae. Caterpillars in warmer outdoor environments
were found to have increased respiration rates, which also correlated to a direct increase
in food consumption (Bennett et al., 1999). Larvae incubated in warm conditions had
drastically higher oxygen consumption rates along with elevated metabolic states (Kukal
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and Dawson, 2002). The increased temperature and food consumption would elevate
growth rates in the larval stage and would increase the rate of metamorphosis. A further
study could look at measuring metabolic rates in larvae in response to low and high
temperatures.
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