Nest Site Selection Influences Mortality and Stress Responses in Developmental Stages of Megachile apicalis Spinola (Hymenoptera: Megachilidae)

• Published in: Environmental entomology 2009-04, Vol.38 (2), p.484-492
• Main Authors: Hranitz, John M, Barthell, John F, Thorp, Robbin W, Overall, Lisa M, Griffith, Justin L
• Format: Article
• Language: English
• Subjects: abiotic stress; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Bees - growth & development; Bees - metabolism; Bees - parasitology; Bees - physiology; Biological and medical sciences; biological invasion; Demecology; developmental stages; ecological invasion; Female; Fundamental and applied biological sciences. Psychology; heat shock proteins; heat stress; heat tolerance; Hot Temperature; HSP70 Heat-Shock Proteins - metabolism; humidity; Hymenoptera; invasive species; Larva - growth & development; Larva - metabolism; Megachile; Megachile apicalis; Megachilidae; Mortality; nest site selection; Nesting Behavior; nesting sites; parasitoids; PHYSIOLOGICAL ECOLOGY; Protozoa. Invertebrata; shade; solitary bees; stress; Stress, Physiological; temperature
• ISSN: 0046-225X; 1938-2936
• DOI: 10.1603/022.038.0223

We examined stress responses and survival in developmental stages of the invasive solitary bee Megachile apicalis Spinola during two nesting seasons in the Central Valley of California to consider whether abiotic stress tolerance of its offspring contributes to this species' successful colonization of the western United States. In 2001 and 2003, artificial nesting cavities were affixed to vertical plywood boards oriented to maximize nest cavity temperature and humidity differences: one side faced south (exposed to direct sun) and the other one faced north (shaded). After several weeks of nesting activity, we measured heat shock protein 70 (HSP70) concentrations in adults and offspring on 1 d in both years and offspring survival and mortality sources in 2003. In 2001, M. apicalis showed higher HSP70 concentrations in exposed nests than in shaded nests during all developmental stages, adults and their offspring. In 2003, overall survivorship was not significantly different between treatments because exposed nests experienced high offspring mortality caused by heat stress, whereas shaded nests suffered similarly high offspring mortality because of parasitoids. In both years of our study, females preferred shaded nests over exposed nests. M. apicalis successfully reproduces in grasslands of the Central Valley of California where offspring survive hot, dry nest sites and parasitoids in sufficient numbers to inoculate new grassland habitats, unpopulated by tolerance-limited native solitary bees, with incipient populations of this bee, M. apicalis.