ABSTRACT: In this study the effects of acute heat exposure on the ability of the fall webworm ( Hyphantria cunea) to maintain stable physiological conditions—well-being— was determined. Larvae were exposed, in a growth chamber, to ambient temperatures, 40˚C or 45˚C for 30 or 90 min. Well-being was determined by observing each subject’s body weight, food intake, fecal production, and velocity of movement during the 24 hours before and after exposure to heat. Groups exposed to heat were not able to maintain pre- exposure levels of body weight, food intake, fecal production, and velocity of movement. Mortality rates were higher in groups exposed to 45˚C and, of those groups; the ones exposed for a longer duration experienced 75% more deaths. These data indicate that fall webworms experiencing web temperatures of 40˚C and 45˚C would face serious challenges in thermoregulation in order to maintain their well-being. INTRODUCTION: Fall webworms ( Hyphantria cunea ) are gregarious lepidopteran larvae that produce silk webs that can encompass large portions of trees. In southern Pennsylvania, larvae and their webs grow rapidly during August and September. Solar heating may dramatically increase temperatures within the web and this heat is expected to warm the larva (Rehnberg 2002). Fall webworm larvae do not leave the web to forage. Instead, they continue to expand the web to contain more foliage. Larger webs are better at reducing the air movement that causes convective cooling (Rehnberg 2002). However, because the webs cannot store heat at night, remaining in the web at night doesn’t offer the larvae extended thermal benefits. The web of the fall webworm does not have heat retentive qualities and air movement does cause interior web temperatures to fluctuate (Rehnberg 2002). The eastern tent caterpillar ( Malacosoma americanum ) is also a web-producing caterpillar. Individuals of this species, in their natural environment, experienced temperatures between 40˚- 50˚C over a period of five hours (Joos et. al 1988). They also display heat dissipative behavior such as hanging from a tree branch or web to reduce contact. However, such behaviors have not been observed in the fall webworm larvae indicating that they are more tolerant of high temperatures and could possibly thrive under them. This study investigated the physiological and behavioral effects of heat exposure on the fall webworm. The Effects of Heat Exposure on the Stability of Physiological Conditions of the Fall Webworm (Hyphantria cunea) Emylee C. McFarland Department of Biological Sciences, York College of Pennsylvania Questions 1.Does exposure to heat significantly alter the well- being of the larvae? 2.Is the change in well-being correlated to the length or the temperature of the exposure? Hypothesis  Decreases in aspects of well-being—body weight, food intake, feces production, and velocity of movement—will be greater in groups exposed at higher temperatures for longer periods of time. Literature cited Joos, B., Casey, T.M., Fitzgerald, T.D., and Buttemer, W.A Roles of the tent in behavioral thermoregulation of eastern tent caterpillars. Ecology 69: Rehnberg, B.G Heat retention by the webs of the fall webworm Hyphantria cunea (lepidoptera: arctiidae): infrared warming and forced convective cooling. Journal of Thermal Biology 27: Acknowledgements Thank you Dr. Rehnberg for your insight, patience, and availability throughout the study.. Future research 1.How do differing levels of humidity affect well-being? 2.What temperatures are fall webworms exposed to within the web? 3.Is web behavior influenced by temperature? RESULTS: 1.Changes in body weight after exposure were not significantly different from the control than was expected by chance. A One-way analysis of variance(ANOVA) yielded a P-value of Differences in food intake were significantly different (P<0.001) between the group experiencing 40˚C for 30 min and the group exposed to 40˚C for 90 min (Figure 2). The difference between the 40˚C 30 min group and 45˚C 30 min were also significant (P<0.01). This was determined by the Tukey-Kramer multiple comparisons test (T-KMCT). 3.Changes in fecal production were extremely significant (Kruskal-Wallis test; P<0.001) between the groups exposed for 30 min and 90 min at 40˚C. This was also observed between the groups at 40˚C for 90 min and 45˚C for 30 min (Figure 2). 4.Changes in velocity were only significant (P<0.05) between groups exposed for 30 min (T-KMCT). 5. Exposure at 45˚C for 90 min resulted in death of 60.87% of the group (Table 1). METHODS: Body weight, food intake, fecal production, and velocity of movement were measured 24-hr before and after exposure to heat in a growth chamber. Temperature probes placed in two locations in the growth chamber were used to monitor the temperature. Humidity was maintained at about 24%. Experiment groups A: control, no exposure. B: 40˚C for 30 min. C: 40˚C for 90 min. D: 45˚C for 30 min. E: 45˚C for 90 min. Heat exposure 1.At the start of each run the temperature in the growth chamber was about 20°C. 2.The temperature was gradually increased over a period of 30 min until the desired test temperature was reached. 3.The test temperature was then maintained for either 30 or 90 min. 4.The trial concluded after a 30 min cool-down period that returned the temperature to 20°C. Measurement procedures 1.Body weight was measured for each subject. 2.Food intake was reached by weighing the portion of food at the start and end of the 24-hr period. Differences due to loss of water were accounted for. 3.Fecal matter accumulated after the 24-hr period was weighed. 4. Velocity was determined by measuring the distance traveled in 30 sec (Figure 1). Figure 1. To determine the velocity of movement the subjects were given 30 sec to move at will on a flat surface. The distance was obtained by measuring the length (cm) of the path traveled. CONCLUSIONS: 1.The ability to maintain a constant body weight was not affected by exposure to heat. Change in velocity was variable throughout and also was not a good measure of heat exposure effects. 2.Webworms exposed for longer periods experienced greater decreases in food intake. However the change was less dramatic when higher temperatures were experienced. 3.Changes associated with the production of feces were equally significant between the test temperatures when exposure time was increased. 4. Internal web temperatures of 45˚C and above will have drastic negative effects when endured for 90 min.