ReadMe for: Spear, Dakota M., Silverman, Sarah, Forrest, Jessica R.K.. Asteraceae pollen provisions protect Osmia mason bees (Hymenoptera: Megachilidae) from brood parasitism. This ReadMe file describes one of the data files that accompanies the above publication, called “sapygid_pollen_experiment.csv”. This file contains data collected for and used within this publication for the sapygid larvae rearing experiment. For details on the collection of this data, and the analyses used, please see the publication. If you have questions or suggestions regarding the data file, please contact Jessica Forrest at jforrest@uottawa.ca VARIABLE NAMES AND DESCRIPTIONS in “sapygid_pollen_experiment.csv”: 1. Year of experiment – experiment conducted in either 2014 or 2015 2. Capsule number – number assigned to the gelatin capsule in which the sapygid larva was raised. The letter A or B next to the capsule indicates the capsule was reused. In 2015, capsules were reused only if a sapygid egg died after transfer and was successfully removed. Note that numbering is specific to each year (i.e., no capsule was reused in multiple years) 3. Date sapygid transferred – the date on which the sapygid egg was transferred into the gelatin capsule 4. Pollen type – type of pollen sample in the gelatin capsule. For information about the flower sources of each pollen type, see appendix table A2. 5. Pollen source species – for Asteraceae pollen, the species of Osmia from which the pollen was collected 6. Pollen type numeric – 1 = Asteraceae pollen, 2 = “generalist” pollen, 3 = Fabeae pollen 7. Sapygid source nest – code identifying the Osmia spp. nest and nest cell from which the sapygid egg was collected. The first part of the code (2-4 characters before the hyphen) is an abbreviation for the site name. The second part of the code identifies the individual nest, by nest block (letter) and nest number within each block. The last part of the code (#X) identifies the cell number within the nest, with the innermost cell = #1 8. Sapygid source pollen – type of pollen found in the sapygid source nest, determined from slides of pollen samples from the inner and outer cells of the original nest, not necessarily the cell the sapygid came from. Blank cells indicate unknown 9. Transfer type binary – for sapygid eggs not transferred to Asteraceae pollen, whether the egg was placed into a gelatin capsule containing the same type of pollen as its original host nest, or a different type of pollen 10. Sapygid egg code – a letter indicates the sapygid egg was taken from an Osmia spp. host nest cell from which more than one sapygid egg was taken 11. Pollen date – the year the pollen sample was collected (2013, 2014, or 2015) 12. Pollen age – the age of the pollen in years when used in a gelatin capsule (either 0 years if the pollen was collected the same year, or 1 year old) 13. Estimated date sapygid egg laid – estimated date the sapygid egg was laid 14. Date sapygid hatched – the date the sapygid egg hatched 15. Date first defecation – the date the larva first defecated. Blank cells indicate the larva died before reaching first defecation stage 16. Date of death – the date the larva died. Blank cells indicate the larva did not die before the end of the study 17. Cocoon start date – the date the larva first started to spin a cocoon. Blank cells indicate the larva died before beginning to spin a cocoon. 18. Cocoon end date – the date the larva finished spinning a cocoon, as indicated by a darkening of the cocoon colour 19. Days – the total number of days the larva lived; that is, the days from the date hatched to the date of death. If the larva completed a cocoon, this is the number of days from the date hatched to the date the cocoon was finished 20. Status – the status of the larva at the end of the experiment. 1 = larva died, 2 = larva was still living