MCMILLAN, D.M.; TROLL, J.V.; RANK, N.E.; DAHLHOFF, E.P.: Survival, growth and effects of environmental stress in larvae of the Sierra willow beetle Chrysomela aeneicollis
The Sierra willow beetle Chrysomela aeneicollis lives in heterogeneous thermal habitats in the Eastern Sierra Nevada. Habitat temperature appears to be a critical factor affecting beetle physiology and genetic variation among populations. To date, most of the research examining temperature adaptation in this beetle has focused on adults. In the summer of 1999, we measured larval survival in three isolated drainages where beetles are commonly found, Bishop Creek (BC), Rock Creek (RC), and Big Pine Creek (BPC). To quantify growth and survival, we collected second-instar larvae from BC, RC and BPC and placed them on willows at a single elevation in each drainage. Larval survival and developmental stage was monitored every 2 d for 3 weeks. Larval survival was independent of source drainage but was lowest in RC, the coldest drainage (mixed-model ANOVA, P<0.005). Minimum air temperature was lower in RC than BC or BPC (P<0.0001) and nighttime temperatures fell below freezing most often in RC (14 of 24 nights). Larvae are exposed to potentially stressful elevated temperatures as well. In summer, larval body temperature routinely exceeds 30oC on warm afternoons. Expression of heat shock proteins (Hsp70) for beetle larvae in nature varied diurnally with air temperature and between sites. Hsp70 expression also depended on phosphoglucose isomerase genotype, a glycolytic enzyme that may be under temperature selection in these beetles. These data suggest that temperture selection may be operating on multiple life history stages in this beetle.
