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Results:

As seen in Figure 12, the average of black color on the larvae was 65% in the cold treatment (6°C to 16°C). As seen in Figure 13, the average of black color on the larvae was 29% in the warm treatment (22°C to 32°C). As seen in Figure 14, the control treatment (17°C to 27°C) showed an average color of 49.5% black and 50.5% light (white and yellow). The significant difference between the three treatments is seen on Figure 15, which shows the difference in the percents of color. The range of yellow coloration was 32.9% (in the warm treatment) to 19.5% (in the cold treatment). The range of white coloration was 38.2% (in the warm treatment) to 15.5% (in the cold treatment). The percent of black coloration ranged from 65% (in the cold treatment) to 28.8% (in the cold treatment).

As seen on Figure 16, the population declined in all of the treatments, but the cold and warm treatments showed a more severe drop in population, and the control treatment had a less extreme decline in larval population. Figure 17 and 18 show that the average masses and lengths of the larvae increased gradually and showed a slight decrease in mass and length near the end of the measuring period. The period in which measurements could be taken lasted from the time at which the larvae are large enough to handle (about second instar level) to the time at which they pupate (directly following the fifth instar level). There was a 423.2 mg drop in average mass and a 4.85 mm drop in average length in the cold treatment. There was a 0.70 mm drop in average length and no drop in average mass in the control treatment. The larvae in the warm treatment had no drop in average mass or average length. As seen in Figure 19, the average instars increased in the warm and control treatments, but in the cold treatment, the second instars were too small to handle, so the measurements were taken at the beginning of the fourth instar level and lasted until pupation.

As seen in Table 1, the larvae in the warm treatment consumed 12 milkweed plants, the larvae in the cold treatment consumed 17 milkweed plants, and the larvae in the control treatment consumed 16 milkweed plants. As seen in Table 2, the average mass of the adult monarch butterflies was 417 mg in the warm treatment, 571 mg in the cold treatment, and 477 mg in the control treatment.

As seen in Figure 20, the three data points fall on the line of best fit with the equation f(x) = A + Bx + Cx2. When A = 45.3, B = 3.72, and C = -0.160, the mean square error in 6.82x10-35, which means that the average deviation from the line of best fit is insignificant.

Conclusions:

The larvae in the warm treatment developed at a greater rate with increased temperature, because increased temperature increases metabolic rate. This increased rate of development from the egg stage to the adult stage was the sole result of temperature and not of the amount of milkweed consumed, because the larvae in the warm treatment consumed the same amount of milkweed per day as the control group. Because the larvae in the warm treatment ate the same amount as the control group per day but developed significantly faster, they emerged as smaller butterflies than the larvae in the control group. As a result of the high temperature, the percent of dark color present on the larvae in the warm treatment was significantly lower than the percent of dark color on the larvae in the control treatment. This indicates that difference in coloration is an adaptation that helps larvae maintain an appropriate body temperature. The high temperature also increased death rate due to high humidity, the brown death (a bacteria found in lab situations that grows inside a larva and eventually kills it), and difficulties molting or pupating, all of which were seen in the experiment.

The larvae in the cold treatment developed at a slow rate with decreased temperature, because lowered temperature slows metabolic rate. Again, decreased rate of development was the sole result of temperature and not of the amount of milkweed consumed, because the larvae in the cold treatment consumed more milkweed than the larvae in the control group. Because the larvae in the cold group ate more than the control group per day but developed more slowly, they emerged as larger butterflies than the larvae in the control group. As a result of the low temperature, the percent of dark color present on the larvae in the cold treatment was higher than the percent of dark color on the larvae in the control treatment. Again, this strongly indicates that dark color is an adaptation to enable the larvae to absorb radiation from the light source to maintain an appropriate body temperature. The lower temperature also increased death rate. Another issue was the original temperature of the climate. The temperature was initially set from 6°C to 16°C, however, the eggs did not hatch at that range. After day nineteen, it was decided that the best course of action was to remove the eggs from the cold and see if the eggs could hatch at all. Refusing to completely give up on the eggs, the temperature in the climate was increased to 20°C during the day. The three degree difference was enough for the larvae to hatch. One problem that followed the temperature change was that the larvae hatched at different times. When the majority of larvae were large enough to handle, some of the larvae had already reached the fifth-instar level. As a result of the variance, the instar levels, lengths, and masses were greatly different. This explains why the average lengths, masses, and instars were so small.

All results at the control temperature fell directly between the cold and warm treatments with the exception of population. The population for the control treatment was larger than the normal population of the cold and warm treatments, because there was little death, given ideal conditions of humidity, food, and pupating/molting not present at normal temperatures. The average masses, lengths, and instars increased in a similar way as the warm treatment, but remained a median between the cold and warm treatments. The dark color on the larvae in the control treatment comprised about fifty percent of the larvae’s coloration, a fact which also places it about halfway between the cold and warm treatment. It also proves that at normal temperatures, larvae will most likely not develop extremely dark or extremely light colors.

The percent dark color had an indirect relationship to the temperature. The data collected in this experiment were almost an exact fit to the line of best fit. The mean square error is so insignificant that it may as well not exist.

To further proceed in this study, there are questions that could be address. First how the humidity affected the growth of the larvae, because the humidity was a factor that was not, how the abundance of food affected the growth, how the two different types of milkweed affected the growth, if there was any chance of the larvae hatching at the original temperature in the cold climate, how cold would it have to be before the larvae cannot hatch, how warm would it have to be before the larvae cannot hatch, what an adequate control temperature under ideal conditions would be, would the results have been different if the temperature was not fluctuating during the day, if the sixteen hour day was an appropriate length for the temperatures, if the constant light during the day was too strong for the larvae, and how the absence of shade affected the larvae.

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Bibliography:

Donnelley, Elizabeth. "Journey North." Annenberg & CPB Math and Science Project August 1998. Learner. Online. Netscape. 25 Sept. 1998.
Address: http://www.learner.org/jnorth/

James, David. "Thermoregulation in Danaus Plexippus (L.) (Lepidoptera Nymphalidae): Two Cool Climate Adaption." Diss. Macquarie University, 1986.

Kuda, Kristen and Oberhouser, Karen. A Field Guide to Monarch Caterpillars. St. Paul: National Science Foundation, 1997.

Oberhauser, Karen. Monarchs in the Classroom. St. Paul: National Science Foundation, 1997.

Oberhauser, Karen. Personal interview. a series of interviews beginning 6 June 1998 and ending 25 Sept. 1998.

Prysby, Michelle. Personal interview. a series of interviews beginning 6 June 1998 and ending 25 Sept. 1998.

Prysby, Michelle. "Impact of Natural Enemies on the Survival and Foraging of the Lepidopteran Herbivore, Danaus Plexippus." Diss. University of Minnesota, 1998.

Solensky, Michelle. Personal interview. a series of interviews beginning 6 June 1998 and ending 25 Sept. 1998.