Chrysomela aeneicollis (willow leaf beetle) enclosure experiment to determine preferred overwintering sites

The "High Stream Crossing" site that is fairly accessible, yet has sustained excellent populations of willow leaf beetles. I covered a small Salix orestera bush with 2.5 x 2.5m mosquito net, and pinned down the edges with sticks, rocks and soil so that nothing could enter or escape.

Inside I placed a small pile of rocks (about 15-25 cm diam each) near the bottom of the enclosure away from the base of the plant.

I also put in a hard clump of dry pine leaf litter, as a possible microhabitat where beetles could overwinter safe and dry

I also added a rotting log about 10 cm in diameter, with many cracks where beetles could hide.

This sketch shows the layout of the experiment. Note that the willow stems form a band across the upper part of the plot and that the experimental habitats are placed away from the bases of the willows.

Here is the experiment 2 days before taking it down (10-31-11)

Note the dried aerial leaves visible through the netting.

A view from the east showing the location and placement of the experiment.

Pine litter ball (center) viewed prior to take down.

Base of the willow plant viewed through the netting prior to take down.

Another view of the habitat before takedown.

Another view of the base of the plants before take down.

The rock pile before removal.

Field notes showing order of takedown.

Rolling up the edges of the enclosure. Note the white frost/ice on the rock and netting adjacent to the rock. It was fairly difficult to peel the netting away from the frozen ground.

Rolling up the netting. The rolled ball was put in bag "A" and searched for beetles in the lab. One was found!

After removing the netting the aerial dried willow leaves were removed by hand, falling onto the tarp below.

Then the ground (mainly non-willow) leaves were removed and stuffed into a bag.

I then removed the "habitats" including the soil under the rock pile, under the rotten log, and the pine litter ball.

I broke apart the rotten log. I found no beetles hiding inthe cracks.

After collecting the superficial leaf litter near the plant base, I collected the litter away from the plant base. Then I started removing the soil from around the plant base, pulling up the stems as I worked.

More digging and stem removal. There were still roots remaining after this process and I expect the willow to resprout next spring.

I then dug up soil from above the plant stems, from below the stems (between .5 and 1 m away), and from the ground away from the plant base (>1m). Here is a veiw of the completed takedown showing what was left behind.

Bags to be transported to the laboratory.

The backpack and more bags. I had to make two trips to carry it all down. 17 bags.

Back in the lab the next day, I spread the soil sample out on a stainless steel table. I began sifting through the soil looking for beetles. As long as they remained dormant they were very hard to find, but eventually then began crawling. Then they were easy to spot.

I put the live adult beetles in a solo cup cooresponding to the bag they were from. I found a few dormant beetles while sifting, but after being put in the cup they all became slowly active. I added some fresh willow to the cup but feeding was minimal.

Before spreading the samples I weighed them to get an idea of how much soil was to be sifted. Here are the lab notes, including the number of beetles collected from each bag. A total of 51 beetles were found.

The results can be summarized in the sketch above. Bottom line: the beetles are by far the most common near the base of the plant, in the decomposing leaf litter/soil layer.

This schematic shows the distribution a little more clearly, as well as beetle density estimates in the soil:

They are hard to see!

The soil samples had a lot of other critters crawling around. Here is a beautiful pattern-winged fly.

Note the orange coloration of the spots. Newly eclosed adults have green spots that turn orange as they prepare for daipause.

Below are photos of the soil samples...