Monday, December 12, 2011

Cleaning Bees, Nov. 20, 2011

We visited the Sturm Farms on November 20, 2011 to remove the bees from their nests and prepare them for the winter. This year we expected to clean lots of nests, so Jerry brought three cleaning machines. Jerry (far left), and John (far right) spent most of the day cleaning nests. In the morning, Rosie (center) also helped on the middle machine. Eric Mader from the Xerces Society joined us to see how it's done. In the afternoon, Mike, the project engineer, visited, and Glen (center) manned the machine.

In the 2011 season we were interested in increasing Osmia lignaria populations as well as O. aglaia, and that created a problem for cleaning out the bees. Although the two bees typically use different diameter nesting holes, apparently many of the O. lignaria were small enough to nest in the O. aglaia Binderboard. That presented a problem cleaning the bees, because we wash the O. lignaria cocoons to remove dirt and other debris and to wash off mites, whereas we don't wash O. aglaia cocoons. There was also a risk that if the bees nest together, mites will transfer to O. aglaia cocoons. We haven't seen mites on O. aglaia before.

We saw few if any mites on the O. lignaria nests, and didn't see any on O. aglaia. There were only a few Binderboard that had nests of both species. However, there were quite a few O. lignaria cocoons infected with Monodontomerus parasitic wasps. I removed as many as I could identify from the washed cocoons. Our final yield of O. lignaria was only 1.25 cups of cocoons with about 236 females per cup. Females were 35% of the cocoons. That means our total yield of females was about 300, enough to pollinate an acre of fruit trees, in theory. Compare that with a yield of 420 females from Sturm farms in 2010 that were released in spring 2011. To that we added about 90 additional females from other sources in Portland. That means our yield was about 58% of last year's yield. Not good.

The O. aglaia did not fare much better. Last season we removed about 31 cups of cocoons from the nests, with and estimated 21,700 bees. We did not try to estimate sex ratio. This year our total yield was about 10.3 cups, with about 650 cocoons per cup. That's only 6,700 cocoons total, 31% of last year's yield. Many of those cocoons had larvae in them that had not fully developed into adults. That suggests that the summer was not warm enough for the bees to complete development. We had the Sturms leave the cocoons in their garage for a month or so, in hopes that the temperatures would be warmer than on the porch where the cocoons have overwintered in the past. Hopefully more of the cocoons will complete development.
Why such a poor bee yield in the 2011 season. Certainly the cold, wet, late season must have had an impact. But perhaps the high numbers of honey bees also had an impact. There may not have been enough pollen for everyone.

Don says that the berry yields suffered from disease this past season, but the black raspberry had good pollination. Perhaps the presence of our managed native bees had a positive impact on the pollination, even if they did not reproduce as well as we would like.