Introduction

1. Depression of Growth Rate in Manduca sexta Larvae Exposed to Frost Poster author names would go here Discussion In our experiment, we found that there were significant relationships between the growth rate of the larvae and the highest temperature that the larvae were exposed to. The larvae had the highest growth rate when their environment was at the highest temperature. In addition, there was a noticeable difference, though not statistically significant, between the larval growth rate in the cold groups and the warm groups: the warm groups had a higher growth rate than the cold groups. Although our experiment did not significantly demonstrate that the cold groups of larvae grew slower than the warm group, the fact that the biggest growth rates occurred at the highest temperatures illustrates some effect of temperature on growth rate (Figure 4). In other studies done on worms and caterpillars, scientists have proven that they grow slower under cold temperatures and faster under warm temperatures (Woods et al. 2003). This can be true even to such an extent that the instar periods will elongate or shorten respectively which would correspond with our results (Levesque et al. 2002). The other significant relationship we found was one between the larval growth rate and amount of change in the temperature of the larva’s environment. The growth rates of the larvae exposed to the frost were significantly lower than the growth rates of their control groups for the remainder of the experiment. These results suggest that the larvae that were exposed to the largest temperature change were still reacting to the cold temperature, in which they have slower growth rates, even after they were brought back to a warmer temperature. The diminished growth rates lasted longer than the actual period of frost exposure suggesting that ectothermic organisms have prolonged reactions to extremely low temperatures even when only exposed for a short while. The detrimental effects of a large temperature change on larvae is consistent with studies where it was demonstrated that such conditions can slow growth because the organisms studied exhausted their energy reserves (Renault et al. 2002). Technical difficulties with the temperature chambers probably impacted our data. The actual temperature inside the chambers varied greatly to the point where the chambers were at some times the same temperature, when they were supposed to be significantly colder or warmer from each other. This might have been one cause for the fact that there was no significant difference between the growth rates of the warm and cold larvae in the control or in the frost groups. Introduction Manduca sexta is a common species of moth whose range stretches from the northern United States to Argentina. Because of their wide dispersal, M. Sexta, in both their adult and larval form, are exposed to a wide range of temperatures and climatic conditions during their generational period from May to October. M. Sexta is a poikilothermic organism, an organism whose body temperature changes with environmental temperature, and an ectothermic organism, an organisms whose body heat is absorbed from the environment. As such, it is to be expected that the ambient temperature of the M. Sexta’senvironment will have a significant effect on their metabolic activity and growth rate. Indeed, studies have shown that temperature has had a rather significant effect on the growth rate of M. Sexta larva with higher temperatures corresponding to greater growth rates (Kingsolver and Woods 1997). Cold temperatures were found to prolong the growth, or instar, periods in M. sexta and thereby decrease the relative consumption rates and growth rates (Stamp and Horwath 1992). In these studies, however, the temperature has been kept constant within temperature groups. The present study set out to investigate the effect on the growth rate of M. Sexta larvae when they were exposed to a precipitous loss of temperature such as might occur during an evening frost in the northern part of their range. This might indicate whether an ectothermic and poikilothermic organism’s reaction to cold temperatures is of a longer duration than the initial exposure to that temperature. Results The highest temperature that the larvae were exposed to was found to have a significant effect on growth rate (one-way ANOVA: F=3.815, d.f.=3, p<0.05). This is especially apparent in the groups after the frost with the greatest growth rate corresponding to the groups that reach the highest temperature (Figure 2). Although not significant, there was an appreciable difference between the groups that were frosted and their respective control groups (one-way ANOVA: F=0.451, d.f.=1, p<0.1). The temperature change also had a significant effect on growth rate (one-way ANOVA: F=3.390, d.f.=4, p<0.05). The frost groups experienced the greatest temperature change after they were removed from the frost and had a lesser growth rate than the control groups which did not experience a large temperature change (Figure 3). Materials and Methods ·Twenty-eight first-instar Manduca Sexta were gathered and evenly divided into four groups: warm control, warm frost, cold control and cold frost. ·Each caterpillar was individually weighed and placed in its own plastic cup with a small cube of artificial diet. ·The two cold groups and the two warm groups were placed into separate temperature chambers (Figure 1) wherein all conditions other than temperature were kept constant, including lighting which was kept at a constant 14-hour day and 10-hour night. ·Both temperature chambers were initially set at 15 C. The temperatures of the chambers were increased periodically to simulate seasonal warming with the warm chamber temperature increased at a faster rate than that of the cold chamber ·The M. Sexta continued to be measured every other day. ·After 10 days in the chambers, the warm frost and the cold frost groups were placed in a different temperature chamber set at 10 C for 8 hours in order to simulate a frost while the two control groups remained in the original chambers. ·After the frost, the experimental groups were returned to their original chambers. The experiment then continued as before the frost for 7 days. ·The average growth rate for each larva and each group was calculated for the periods before and after the frost. A one-way ANOVA test was then performed to determine which factors of the experiment significantly affected the growth rate of the larva. Figure 2. This graph shows the relationship between the growth rate of the larvae for each group and period and the highest temperature that the larva were exposed to for that period. CC designates the cold control group, CF the cold frost, WC the warm control and WF the warm frost with a and b referring to the after and before frost periods respectively. Growth rate for each group is an average of the growth rate for the seven larvae in the group. Error bars represent the standard error of the means. Figure 4. Representative caterpillars from each group at the end of the experiment Literature Cited Kingsolver, J. G., and H. A. Woods. 1997. Thermal sensitivity of growth and feeding in Manduca sexta caterpillars. Physiological Zoology 70:631-638. Levesque, K. R., M. Fortin, and Y. Mauffette. 2002. Temperature and food quality effects on growth, consumption and post-ingestive utilization efficiencies of the forest tent caterpillar Malacosoma disstria (Lepidoptera : Lasiocampidae). Bulletin of Entomological Research 92:127-136. Renault, D., C. Salin, G. Vannier, and P. Vernon. 2002. Survival at low temperatures in insects: What is the ecological significance of the supercooling point? Cryoletters 23:217-228. Stamp, N. E., and K. L. Horwath. 1992. Interactive Effects of Temperature and Concentration of the Flavonol Rutin on Growth, Molt and Food Utilization of Manduca- Sexta Caterpillars. Entomologia Experimentalis Et Applicata 64:135-150. Woods, H. A., W. Makino, J. B. Cotner, S. E. Hobbie, J. F. Harrison, K. Acharya, and J. J. Elser. 2003. Temperature and the chemical composition of poikilothermic organisms. Functional Ecology 17:237-245. Figure 1. Manduca sexta growth chamber Figure 3. Graph of the relationship between the average growth rate of the larvae for each group after the frost and the temperature change that the larva were exposed to for that period. Error bars represent the standard error of the means.