We examined stress protein levels in egg, larval, prepupal and pupal stages of the invasive, leafcutting bee Megachile apicalis during exposure to high temperatures in the field. Previous studies demonstrate that this species routinely occupies high-temperature habitats in the Central Valley of California and, under both field and laboratory conditions, prepupae withstand temperatures that reach 50 oC. We designed a field experiment to test stress levels of different developmental stages of this bee species in exposed (direct sun) and unexposed (shaded) nesting conditions. Sampling units with nesting cavities were hung from sheets of plywood standing vertically in open areas surrounded by yellow star-thistle (a preferred host-plant of the bee). One side of each board faced S while the other side faced N to maximize temperature differences during the hottest period of each day. After about five weeks, nest contents were removed and immediately frozen during the hottest period of a day in August. Temperatures in nest holes on the exposed sides of boards exceeded 45 oC during several hours of the sampling day while the shaded sides of boards never reached 40 oC during the same time period. Levels of a stress protein, heat-shock protein 70 (hsp70), were then measured using an ELISA method. Hsp70 levels in eggs and larvae exposed to the sun were significantly higher than those in the shade while prepupae and pupae did not show substantial differences between treatments.
Species 1: Hymenoptera Megachilidae Megachile apicalis (leafcutting bee)
Keywords: heat shock proteins, nesting site
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