FLOWER PRODUCTION AND HONEY-BEE DENSITY EFFECTS ON MEADOWFOAM SEED YIELD

Meadowfoam (Limnanthes alba Hartw. ex Benth. subsp. alba cv. Mermaid) is protandrous and entomophilous. Flower number and phenology, stigma receptivity, and timely honey bee pollination are highly weather dependent and were hypothesized to cause seed yield variation. The objective of this field experiment was to use a synchrony index, which is an estimate of flower receptivity and pollination timing synchrony, to relate variation in seed yield to number of open flowers and foraging honey bee (Apis mellifera L.) density. Transparent floating crop-cover and shade cloth were used to alter flower number and flower phenology. The soil type was Amity silt loam (fine-silty, mixed, mesic Argiaquic Xeric Argialboll). Cumulated open flowers and cumulated foraging bee density were derived from daily counts of flowers and foraging honey bees, respectively. Flower receptivity for each day was estimated using maximum air temperature for that day. Number of receptive flowers for each day was multiplied by the number of foraging bees for that day and summed for the bloom period to form cumulated synchrony index. A multiple regression model (R2 = 0.47, P < 0.001) indicated a linear positive association of seeds per flower with cumulated foraging bee density, and a quadratic negative (within the experiment range) association with cumulated open flowers. A simple linear regression explained 87% (P < 0.001) of the variation in seed number per area by difference in cumulated synchrony index. This confirms the importance of pollination timing, foraging honey bee activity, and total number of flowers for achieving high seed and oil yields and emphasizes the need for careful management and monitoring of these variables.