ASU Research E-Magazine: Bagging an Umbel

During her study of agave plants, ASU botany student Liz Slauson focused on determining the effectiveness of day versus night pollinators. To do so, she had to devise a method to control access to specific plants she was observing. A bit of mesh netting proved to be just the right tool.

Slauson blocked access to certain plants so she could control who visited them. Using the fine netting, she covered the flower clusters, or umbels, from several Agave palmeri and Agave chrysantha plants. The nets prevented creatures larger than 1.5 millimeters from reaching the flowers.

The bags were an elegant solution. However, the steep, thorny agave habitats and size of the plants’ flowering stalks made “bagging” the umbels no easy feat. Agaves range from about seven to 21-feet tall.

Slauson and her volunteers assembled long poles with hooks that carefully dropped the nets over the umbels, then closed them with a drawstring device. It was a time-consuming process. Volunteers dodged tedium by racing against the clock.

“The record was 30 minutes for 15 plants, and that included travel time,” Slauson says.

Umbels were assigned to one of the following treatments:

Bagged at sunset and unbagged at sunrise, making them available only to day visitors.
Bagged at sunrise and unbagged at sunset, allowing access only to night visitors.
A control group, open to day and night visitors.
Bagged for 24 hours, but liberally hand-pollinated during stigma receptivity, to see what optimal fruit set would be.

To hand-pollinate, Slauson dipped a paint brush into pollen collected from other plants, then slathered it onto the experimental plant’s stigma.

When it came to staving off day visitors, the early bird beat the bee. The researchers sometimes had to be on site as early as 3 a.m. to bag the umbels.

“The bees were mostly a pain,” Slauson says. “As soon as there was any light, they were up. And as soon as they’d go to sleep, we’d take off the day nets and put on the night ones.”—Amanda Kingsbury