Tent caterpillars are robust to variation in leaf phenology and quality in two thermal environments Rana M. Sarfraz*, Heather M. Kharouba and Judith H. Myers Department of Zoology, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 Abstract The synchrony between emergence of spring-active, insect herbivores and the budburst of their host plants could be affected by warming temperatures with influences on the availability and quality of foliage as it undergoes physical and chemical changes. This can affect the growth and survival of insects. Here, we used sun-exposed and shaded trees to determine whether the synchrony between egg hatch of western tent caterpillar, Malacosoma californicum pluviale Dyar (Lepidoptera: Lasiocampidae) and budburst of its host red alder, Alnus rubra Bongard (Betulaceae) changes with different thermal environments (temperature and light together). To explore the potential outcome of a shift in phenological synchrony, we used laboratory assays of larval growth and survival to determine the effect of variation in young, youthful and mature leaves from sun-exposed and shaded trees. While the average higher temperature of sun-exposed trees advanced the timing of budburst and egg hatch, synchrony was not disrupted. Leaf quality had no significant influence on growth or survival in the laboratory for early instars reared as family groups. Later instar larvae, however, performed best on mature leaves from sun- exposed trees. The robust relationship between leaf and larval development of western tent caterpillars suggests that warming climates may not have a strong negative impact on their success through shifts in phenological synchrony, but might influence other aspects of leaf quality and larval condition. Keywords: phenology, synchrony, insect fitness, leaf quality, climate warming, forest Lepidoptera, western tent caterpillars (Accepted 13 December 2012; First published online 7 March 2013) Introduction Warming climates have the potential to modify the inter- actions among species with uncertain outcomes on popu- lations and communities (Donnelly et al., 2011). In particular, the synchrony between the emergence of spring-active defoliators and the budburst of their host plants could be affected by increasing temperatures (Parmesan, 2007; Both et al., 2009; Singer & Parmesan, 2010; Donnelly et al., 2011). Synchrony between these two events is thought to enable these insects to feed on newly flushed young leaves that are generally nutritionally superior to older foliage (Feeny, 1970; Larsson & Ohmart, 1988; Hunter & Elkinton, 2000; van Asch & Visser, 2007). Typically, as leaves mature, leaf toughness increases, water content decreases, foliar sugar/protein ratio shifts from protein-dominated to sugar-dominated com- pounds (Ayres & MacLean, 1987; Haukioja et al., 2002) and tannins tend to increase in older foliage (Feeny, 1970). *Author for correspondence Phone: (604) 822-2131 Fax: (604) 822-2416 E-mail: rsarfraz@zoology.ubc.ca Bulletin of Entomological Research (2013) 103, 522–529 doi:10.1017/S0007485312000892 © Cambridge University Press 2013