Manzanita

Pollinators and Nectar Robbers on Manzanita (Arctostaphylos sp.) – results from a second field trip

In a previous post I wrote about finding a Manzanita in bloom in early February. One of the questions I asked was: Who is making the holes I see on the sides of the Manzanita flowers? I did some research and some email queries and got the suggestion that these may be made by thrips.

Last Sunday, Feb 17, I went out to find and photograph more manzanita. I didn’t have much time so I needed to go to the nearest area possible. I went to Molino Basin Campground in the Santa Catalina Mts. at 4500 ft. About an hours drive. I only had a little time but the trip was very successful.

  • None of the plants that I looked at had open buds.
  • On some, the budding had just begun.
  • On others all the buds were dead.
  • On still others there were flowers ready to open but untouched as far as holes or visitors.
  • On one I found extensive holes and three species of bees and one unknown fly.

I took pictures of two species of bee and spotted one other, Apis melifloris. I also spotted one unknown fly. I picked one of the damaged flowers and while inspecting it noticed that there was a thrip on my hand. It got away but I put 6 flowers in a specimen jar and by the time I got home it had about 9 thrips in it. They had to of come from the damaged flowers. The thrip in the image is taken through the jar and so it is the underside. All these images are full size so one can view them quite close. The thrip has banded wings so it is probably (Orothrips sp.). I also took two small branches, one from a damaged plant and one from a pristine one. The base where I cut each twig was about 2 mm in diameter. On the damaged stem there were 19 clusters with an average of 8 flowers per cluster. On the undamaged stem there were 29 clusters with an average of 9 flowers per cluster. I looked at and counted most of the flowers on the damaged plant and all of flowers on the undamaged plant. The damaged plant had about 30% undamaged flowers while the undamaged plant had 100% undamaged flowers. I put them in water in my house and the next day (Monday Feb 18) the flowers on both plants opened. Also, many of the damaged flowers fell off. On Wednesday (Feb 20) I looked at the plants again:

  • Some of the damaged flowers that fell off seem to be setting fruit
  • I noticed holes now in some of the undamaged flowers

I picked some of the newly damaged flowers and examined the holes under a 16x glass. The hole was plainly visible and I also saw a small dark dot on the surface of the flower next to the hole. I don’t have any higher magnification available so I took a macro at an angle to see if the dot had a thickness. It very much does. I found a second flower with the same hole and dot combination.

Conclusions:

  1. The flowers on this stem looked pristine when I examined them. The dots are very tiny so I might of missed them. Or they could have appeared after the flowers opened. My hypothesis is that they are thrip eggs and that when they hatch a hole is somehow made. Perhaps the egg itself pierces the petal. The elasticity of the petal might be pulling the hole apart. This doesn’t mean that bees might be enlarging the hole and perhaps some bees are cutting their own holes, just that I now believe thrips are involved.
  2. Not sure, but it looks like some of the damaged unopened flowers may have been pollinated. Whether by self pollination or by thrips or by bees I don’t know.

These are full images, they can be zoomed-in to get more detail.

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