Calculations and Monitoring the Progress of the Bees - 18 June 2020

Now that we have significant bee activity at our Gilbert Site1a2h, we will be monitoring the progress as they fill the habitat tubes.

We have updated the Home page, to include an overall status for the two sites in Gilbert and Payson/Flowing Springs.

Now that we have some significant data, we can do some simple calculations.

First, the count for 18 June is 246:

Site1a2h Results as of 18 June 2020

The count by day with a linear trend line is as follows:

Site1a2h Results as of 18 June 2020 - Trend

We first observed the bees on 30 May 2020 and started counting tubes filled on 4 June 2020. If we linearly interpolate backwards using the entire sequence above, we get

count = 13.4285714285714*days + 39.4285714285714

Count equals zero (start point) is then estimated to be on 1 June 2020.

If we do the linear fit using the values from 6 June to 12 June (because we under counted on 4 June due to not counting the "back" side of the large habitat AND the count increase is falling off as we near completion) we get the result:

count = 16.5*days + 21

Count equals zero (start point) on 30 May 2020.

Either of these would support a start date of the activity on 30 May 2020 as observed given a day or two for all the bees to emerge and mate.

Our motivation for seeing if we can propagate and increase a leaf cutter bee population in the 'hot' Arizona environment is the same as this article:

The U.S. imports this bee by the gallon. Why can't we raise our own?

"Every year farmers spend thousands of dollars to purchase larvae from bee brokers in Canada. The bees are sold by the gallon and shipped into the United States. In 2016, more than 70,000 gallons of leafcutter bees were exported from Canada.
But these bees struggle to reproduce. Most of their offspring die in the U.S. — it averages out to a half a bee surviving per female leafcutter imported. However, each mother bee in Canada can produce about two and a half larvae." 

And this graph:

Alfalfa Leafcutter Bees Imported From Canada

Elisabeth S Wilson, Department of Biological Sciences, North Dakota State University who is the focus of the article above estimates about 6 offspring per nest for leaf cutter bees:

Leaf Cutter Offspring Per Nest by Elisableth Wilson

Using the 6 offspring/nest and assuming a 2 to 1 male to female ratio (leads to two females per tube) our 246 tubes filled (although we should subtract the 'mud filled' Blue Orchard Bee tubes) leads to about 400 - 500 female cocoons leaving aside losses due to other factors.

We estimated that we started with 843 female bees so we are still below reaching break even. But some of the females may have gone elsewhere.

So we have the start of some numbers that we can analyze. One interesting number would be how many 'nests' (tubes) does one female typically fill in a life time? Given that we could estimate how many female bees created our nests and how many 'flew' away and nested elsewhere.

Here's a video report for today's activity.