Page Banner

United States Department of Agriculture

Agricultural Research Service

Pollen Balls
headline bar

“Pollen Balls:”
A Big Problem in Alfalfa Leafcutting Bee Production

In the early years of alfalfa leafcutting bee production, U.S. farmers had been able to produce enough bees for pollinating their own alfalfa, and then have some bees left over to sell to other farmers.

Today, many U.S. farmers have poor bee production and purchase a large proportion or all of their bees annually from commercial suppliers, who are usually from Canada.

Chalkbrood is a major problem in some alfalfa seed-growing regions where farmers try to manage their own bees, but in almost all areas, a moderate to high proportion loss of commercial bees is the unexplained death of the egg or young larvae, oftentimes referred to as “pollen balls”.

Pollen balls might also refer to cells in which a provision was made, but apparently no egg was ever laid.

There is much speculation about the causes of early immature mortality, but only some of these potential causes have been thoroughly investigated.

One reason for the difficulty in studying this problem is that it represents many types of non-productive cells with no brood or dead, young brood.

Complicating this matter is the assessment of the quality of bees as overwintering prepupae using x-rays.

With x-rays, one can clearly distinguish live prepupae, larvae infected with chalkbrood, and cells with parasites and pests.

The other cells that show a pollen mass, but none of the other contents just mentioned, are most often lumped as “pollen balls.”

Therefore, “pollen balls” is a mixed-bag of cells that are "duds".

Only by knowing the true contents of “pollen ball” cells will we be able to address true mortality factors.

We have been opening cells identified as “pollen balls” on x-ray to see what is inside and re-categorizing them.

We are finding out the actual contents and moisture condition of so-called “pollen ball” cells.

Then we determine if the moisture condition and contents of pollen ball cells are equivalent among bee populations from different bee producers.

With more information, we are posing new research questions for discovering the reasons for these non-productive cells according to location or grower with the objective of finding appropriate solutions for better bee yields.


Last Modified: 4/8/2009