Author
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Pitts Singer, Theresa |
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Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/24/2015 Publication Date: 6/13/2015 Publication URL: http://ee.oxfordjournals.org/content/ee/44/4/1125.full.pdf?ijkey=JdpDGiPXevMocK7&keytype=refDOI: 10.1093/ee/nvv088 Citation: Pitts Singer, T. 2015. Resource effects on solitary bee reproduction in a managed crop pollination system. Environmental Entomology. 44(4):1125-1138. Interpretive Summary: The number of alfalfa leafcutting bees released for pollination in a managed alfalfa seed field and the number of flowers available for feeding bee offspring may affect how the mother bee uses floral resources to make more or less offspring, or offspring of the larger sex (females). Overwhelming, limited, or adequate pollination because of different pollinator numbers may affect crop yield depending on plant response to bee visits. Studies of bees on alfalfa provide a way to ask ecological questions about reproduction theories, as well as examine whether relatively high bee densities can affect the sustainability and pollination efficacy of managed pollinator populations. A multiyear study was performed on three alfalfa plots upon which bee densities were varied. The number of adult bees and open (pollinated or unpollinated) flowers during the growing season was recorded; information about bee reproduction was collected in the winter. Results showed that when the number of bees per flower increased, the percentage of pollinated flowers increased, while the pollinated flowers per female bee decreased. Also, if bees per flower increased, then healthy brood production, but not their weights, also increased. Contrary to studies with caged bees, alfalfa leafcutting bee offspring number, sex, and size were not affected by limited floral resources or choices made by mothers on what resources to invest in her offspring. Another consideration is that the number of females released in the fields may have caused them to disperse prior to the need for bees to respond through having to ration food resources for offspring production. Technical Abstract: The number of solitary bees (Megachile rotundata) released for pollination in a managed system (Medicago sativa seed production) and the number of flowers available for brood provisioning may affect reproduction through maternal resource allocation and investment. Overwhelming, limited, or adequate pollination because of different pollinator numbers may affect crop yield depending on plant response to bee visits. Studies of this bee-plant system provide an empirical test of ecological theories concerning reproduction (Fisher’s, Optimal Allocation, and Conditional Allocation) as well as examine whether relatively high bee densities can affect the sustainability and pollination efficacy of managed pollinator populations. A multiyear study was performed on three M. sativa plots upon which bee densities were varied. The number of adult bees and open (pollinated or unpollinated) flowers during the growing season was recorded; bee reproduction variables were collected in the winter. A calculated Density Index (DI) for each field each year described the number of female bees per available flowers over time. Correlation analyses revealed that DI has a positive relationship with the percentage of pollinated flowers, a negative relationship with pollinated flowers per female, a positive relationship with healthy brood production, and no significant relationship with individual adult offspring weight. Contrary to studies with caged bees, M. rotundata offspring number, sex, and size were not affected by resource limitation or maternal resource manipulation. Other density-dependent factors may have induced a dispersal response prior to the need for bees to respond through manipulation of resources for brood production. |
