Pollination biology and pollinator alternatives in Mermaid meadowfoam (Limnanthes alba Hartw. ex Benth.)

Meadowfoam (cultivar Mermaid) is an entomophilous winter annual oilseed crop that has historically produced an average of only two of five seeds per flower. Reference to inadequate meadowfoam pollination exists in the literature, but quantitative evidence is lacking. Studies were undertaken to: (1) quantify meadowfoam pollination requirements and (2) evaluate the potential of an alternative pollinator. In vivo pollination biology studies tested pollen age, stigma age, stylar restriction, and pollen deposition rate effects on seed set. Yield efficacy of Osmia lignaria propinqua Cresson, a native wild bee pollinator, was compared in cages to a honey bee standard and a non-caged honey bee control. Osmia reproductive potential was also tested. Pollen 0-5 days old (postanthesis), stored at 3, 18, or 37{dollar}spcirc{dollar}C, did not appear to limit seed set. Stigma age was critical for seed set maximization. Seed set was not influenced by the number of stigmas pollinated per flower, but was limited by less than 25 pollen grains deposited per flower. Seed set and pollen deposition increased with increasing honey bee visits per flower. It was concluded that at least three honey bee colonies per acre should be used for commercial meadowfoam production. Osmia produced comparable individual plant yields to honey bees. Sixty Osmia produced similar solid stand yields to 4000 honey bees. Significantly greater solid stand yields per bee were obtained from Osmia when compared to the honey bee. Osmia survival and female production were negatively correlated with female density, while nest/male/total cell production was positively correlated with female density. Osmia demonstrated yield improvement potential as a meadowfoam pollinator.