A Pollen Foraging Behavior

A new era in breeding honey bees began in the 1950’s when artificial insemination became a practical option. Managed crop pollination was in its infancy, and for the next fifty years selection was made on honey production, temperament and disease resistance (Oxley and Oldroyd, 2010). Meanwhile, demand for pollination services grew exponentially and soon became a critical component of US agriculture. Commercial beekeeping was no longer all about the honey, leading to new ideas about which traits had the most economic value. Today, it is not all together uncommon for a healthy colony to expand normally and perform well in the springtime yet fail to store enough honey to last the winter. Is this phenomenon the result of strong demand for a more efficient pollinator?

Fifty years ago, researchers from the USDA bee lab in Logan, Utah discovered that certain behaviors of honey bee foragers were hereditary. Artificial selection can produce high pollen-hoarding strains that store six times as much pollen in just three generations. The increase in stores comes at the expense of honey production. High pollen-hoarding bees are particularly sensitive to stimuli that call for gathering more pollen, and when nectar availability declines, nectar is as good as gone. Come early July along the Wasatch Front, honey production abruptly ends in many areas.

High pollen-hoarding strains have been shown to significantly improve cranberry pollination. Bees foraging protein transfer four times as much pollen to the next flower than a nectar forager. The rate of pear pollination is over 50% when blooms are visited for pollen but falls to under 20% when bees gather only nectar. In the almond groves, at least ten visits by a nectar forager are required for pollination to occur, compared to as little as three by a pollen picker upper.

The market for commercial beekeepers was worth $830 million in 2016. 85% of the pollination market comes from almond growers, represented by the Almond Board of California. Their contribution to beekeeping revenue in 2016 was $272 million — one out of every three dollars. Per-hive fees jumped from $55 in 2004 to nearly $140 in 2006 after large-scale colony losses. A multifaceted response by the almond industry included the formation of non-profit Project Apis m (PAm), whose research has included genetic evaluation of honey bee strains for superior pollinator lines.

Queen producers openly advertise bees that build up rapidly in spring, effectively admitting selection for the pollen-hoarding trait. Recall that a negative correlation exists between pollen foraging (colony development) and nectar foraging (honey production). Honey production declined 9% from 2016 to 2017, and has been gradually declining in the twenty years since the first strain of high pollen-hoarding bees was produced.

Nearly 75% of the nation’s commercial beehives are needed to pollinate California’s almond groves. One thing is clear: selection is for pollen bees, not honey bees. Production queens are an end-product — inbreeding causes substantial loss of vigor in the next generation. The beekeeper must re-queen annually to maintain desired traits.

Rather than an independent, selectable trait, pollen hoarding is more accurately defined as a behavioral syndrome — a framework of multiple, overlapping behaviors that intersect across common gene groups. Selection for pollen-hoarding has far reaching effects: the PHS causes bees to make an early transition to forager, reducing lifespan. Premature foraging is also the driving force behind rapid depopulation of a collapsing colony. Bees from high pollen-hoarding strains require more time to pupate, and longer pupation is why mites prefer drone cells. A logical conclusion: selection for pollen hoarding increases mite loads.

The entire landscape of commercial beekeeping was summed up by Dr Jeffrey Pettis at a congressional hearing in 2014: “We have looked at honey bees as something kind of mystical... They are livestock. And they have one mission and that is pollination...” If there is any hope at all, it lies with those who keep bees close to nature, unmotivated by financial gain.