Plastic sheets on test plots where alkali bees emerge.

PROSSER, Wash. – Huge, colorful plastic squares decorating a farm field in the Touchet Valley may look like works by environmental artist Christo, but they’re really part of an experiment to help producers of alfalfa seed realize higher profits.

Alfalfa farmers in the area produce seed yields that are twice the national average. The sheets are part of Washington State University research to better synchronize the timing of alfalfa blooming with the emergence of its chief pollinator, the native alkali bee. 
 
alkali bee emerges
An alkali bee breaks through the crusty soil in late spring,
ready to pollinate alfalfa.

The bees typically emerge from their ground nests in late spring as alfalfa blooms and are its primary pollinators. Some years, however, the weather interferes. For example, late spring rains may prompt alfalfa to bloom early while delaying alkali bee emergence.

When the pollinators are not available, farmers see a smaller seed crop and reduced sales. This fate could be avoided if farmers could control the timing of alkali bee emergence.
 
Because previous research shows alkali bee pupation and emergence to be dependent on soil temperature, WSU researcher Amber Vinchesi figured plastic sheeting was worth trying to heat and cool alkali bee habitat.
 
She is working on a master’s degree with Doug Walsh, entomologist at the WSU Irrigated Agriculture Research and Extension Center (IAREC) in Prosser. Doug Cobos, an instructor of environmental biophysics in the WSU Department of Crop and Soil Sciences, assisted with data from soil temperature sensors. 
Not a job for honey bees
 
For plants to create seeds, the blossoms need to be pollinated. This comes easier to some plants than others.
 
With alfalfa, the stamen, or pollen-producing part of the flower, is contained in a chamber that must be opened by an insect. When opening the chamber, the insect gets hit on the head by the stamen, which releases a shower of pollen.
 
While honey bees carry a huge burden of pollinating many commercial crops, they don’t much fancy getting crowned by the dusty stamen of alfalfa. They learn instead to carefully extract nectar without tripping the mechanism that releases pollen.
 
Fortunately for alfalfa growers and buyers, the native alkali bee, Nomia melanderi, shows great affinity for the crop. In late spring, these bees emerge by the millions from patches of highly alkaline soil, seek out alfalfa and welcome the shower of pollen that fertilizes the flowers and guarantees a strong seed crop.

Three years of testing has shown that alkali bee emergence can be either sped up or delayed depending on soil surface treatment. White chalk dust and white plastic both reflect sunlight and warmth, which slowed soil warming and delayed bee emergence by a week.

Clear plastic sheeting promotes soil heat retention, which sped up bee emergence by a week to 10 days. Sheeting of other colors also influences soil temperature, but not to the extent of the clear and white plastic.
 
“Some varieties of alfalfa bloom earlier and some later,” said Vinchesi. “By selectively applying plastic or chalk to the soil, farmers can improve the chances that the alkali bees will be available when the alfalfa blooms.”
 
A scientific paper detailing the study was published in the May 2013 edition of Apidologie and is available at http://link.
springer.com/article/10.1007/s13592-012-0180-7
. For more information on research at the IAREC, see http://bit.ly/wsuprosser.