Student Research

Factors Influencing Rates of Pollen Accumulation in Watermelon

Measurements of pollinator performance (the relative success of an organism at pollinating a given crop) are vital to agriculture, especially for crops like watermelon (Citrullus lanatus) which are dependent on bees to set fruit. Pollinator performance is often estimated by bagging a female (pistillate) flower before it opens to ensure a clean or “virgin” stigma, allowing one single visit from a pollinator, then quantifying the amount of pollen deposited on the stigma. However, pollination models based on these measurements can be problematic, as female flowers can accumulate artificially high volumes of nectar while bagged. There is evidence that honey bees (Apis mellifera) deposit two to three times more pollen on flowers with higher levels of nectar versus flowers depleted of nectar, suggesting that the conventional bagging procedure may induce systematic overestimates of pollen deposition, at least for honey bees. This study aims to examine pollen deposition in watermelon beyond the single-visit estimates used in many other studies. Specifically, it will measure rates of pollen accumulation on virgin flowers (depleted of nectar) per unit time by the collective pollinator assemblage at various farms in Southern California. Preliminary analysis of 14.3 hours of bee activity from 2 different farms indicates that honey bee visitation frequency and time of day are significant predictors of pollen accumulation, which can be modeled linearly. Non-Apis bees accounted for only 6% of total observed visits. This study can help establish a purely observational framework for evaluating the pollination services being received in a field.

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