Impact of Bee Species and Plant Density on Alfalfa Pollination and Potential for Gene Flow

Abstract

In outcrossing crops like alfalfa, various bee species can contribute to pollination and gene flow in seed production fields. With the increasing use of transgenic crops, it becomes important to determine the role of these distinct pollinators on alfalfa pollination and gene flow. The current study examines the relative contribution of honeybees, three bumble bee species, and three solitary bee species to pollination and gene flow in alfalfa. Two wild solitary bee species and one wild bumble bee species were best at tripping flowers, while the two managed pollinators commonly used in alfalfa seed production, honeybees and leaf cutting bees, had the lowest tripping rate. Honeybees had the greatest potential for gene flow and risk of transgene escape relative to the other pollinators. For honeybees, gene flow and risk of transgene escape were not affected by plant density although for the three bumble bee species gene flow and risk of transgene escape were the greatest in high-density fields.

The effects of time, temperature and plant variety on pollen viability and its implications for gene flow risk

“…Several native insects, including bumblebees ( Bombus ) and some solitary bees, can pollinate alfalfa (Cecen et al . ; Brunet & Stewart ). In seed‐production fields, honeybees ( Apis mellifera ) and alfalfa leafcutting bees ( Megachile rotundata ) are the most commonly used managed pollinators, while alkali bees ( Nomia melanderi ) are utilised in parts of the Pacific Northwest.…”

Floral traits influencing plant attractiveness to three bee species: Consequences for plant reproductive success

“…This hypothesis is supported by a previous study in which seed set per tripped flower was similar for honey bees and leafcutting bees (Cane, 2002); therefore, the increase in seed set with more visits must result from more flowers being tripped and setting seeds. Female Megachile rotundata can trip 80% of the visited flowers (Pitts‐Singer and Cane, 2011), while tripping is much lower for the males (Cane, 2002), and the tripping rate is lower when external temperatures are cooler (Brunet and Stewart, 2010). Bumble bees are good trippers of Medicago sativa , with B. impatiens averaging a tripping rate of 45–55% (Holm, 1966; Brunet and Stewart, 2010).…”

“…Female Megachile rotundata can trip 80% of the visited flowers (Pitts‐Singer and Cane, 2011), while tripping is much lower for the males (Cane, 2002), and the tripping rate is lower when external temperatures are cooler (Brunet and Stewart, 2010). Bumble bees are good trippers of Medicago sativa , with B. impatiens averaging a tripping rate of 45–55% (Holm, 1966; Brunet and Stewart, 2010). Honey bees tend to exhibit low tripping rates unless temperatures are very high (Bohart, 1957; Cane, 2002), and they are known to avoid the tripping mechanism by stealing nectar from the sides of M. sativa flowers, which limits contact with the plant's sexual structures (Bohart, 1957).…”

Practices that Support Coexistence: A Survey of Alfalfa Growers

“…Research focused on how foraging interactions between multiple species of commercial pollinators influence the movement of transgenic pollen would be beneficial. Also, research focused on pollen movement by native pollinators would be beneficial since previous research has indicated that they can be effective pollinators (Brunet and Stewart, 2010; Van Deynze et al, 2008). Producers of AP‐sensitive alfalfa seed have expressed concern that the movement of honey bee hives and leafcutting domiciles may contribute to the dispersal of genetically engineered pollen.…”