Abstract
Nutritional studies often require precise control of nutrients via dilution of artificial diets with indigestible material, but such studies in bees are limited. Common diluents like cellulose typically result in total mortality of bee larvae, making quantitative studies difficult. We investigated potential alternative dietary dilution agents, sporopollenin (pollen exines) and agar. We reared Osmia bicornis larvae on pollen diluted with these substances, alongside undiluted controls. Sporopollenin neither prevented nor improved survival, suggesting it is a suitable diluent. Agar appeared marginally to increase survival and its suitability requires further research. Both substances reduced cocoon weight, and sporopollenin also prolonged development, suggesting processing costs. Determining the physiological mechanisms driving these responses requires further work. Our findings should facilitate studies involving nutritional manipulations for solitary bees.
Highlights
Artificial diets are integral to studies of animal nutritional ecology, because they allow hypothesis testing using controlled manipulation of constituent nutrients (Roulston and Cane 2002)
Consistent with this, in pilot trials, we found that substituting the original pollen balls with replacements consisting of 70% honeybee pollen and 30% powdered cellulose resulted in total mortality of Osmia bicornis larvae within a few days
Our findings suggest that sporopollenin is a suitable dilution agent in artificial diets for bee larvae
Summary
Artificial diets are integral to studies of animal nutritional ecology, because they allow hypothesis testing using controlled manipulation of constituent nutrients (Roulston and Cane 2002). Most model bee species are highly social, which is problematic for studying larval nutrition: in the most social species, foragers contribute nutrition to a collective pool that is used to feed larvae, obscuring individual feeding relationships (Schmickl and Karsai 2016). Any such studies must either use intensive in vitro feeding of individual larvae By manipulating or replacing the pollen ball, we can study larval health directly (Levin and Haydak 1957) Despite this opportunity for experimental research, solitary bee nutrition is relatively poorly studied (Roulston and Cane 2002; Filipiak 2019). In a recent study of pollen nutrition, researchers resorted to harvesting natural provisions from bee cells in the field to provide a suitable base for minimal manipulation, adding only protein-rich royal jelly (Fischman et al 2017)
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