Tuesday, November 16, 2010

A Plague of Leaf Cutter Bee

When I saw this little plant, I classified it as a model of an insect plague. Here we have a plant population, a population of one, and a swarm of attacking insects, probably also represented by a single individual. Will this match have a clear winner and loser?

The plant, a Moonseed, Menispermum canadense, is a short sprout produced from a stump left when something bit the vine off at ground level. This makes it a stressed individual and stress in a plant often sends signals to insects that advertises an appetizing meal.

I posted earlier about the abundance of Leaf Cutter Bees at Blue Jay Barrens this year. Leaf Cutters cut circular pieces out of leaves to use as a lining in their underground brood chambers. It looks like about half of the total leaf area was removed by the bee. The plant began with only five leaves, so it only had the equivalent of two and a half leaves to provide energy to what was probably a pretty substantial root system. Looks like the stress is increasing in this plant.

The small veins seem to do a good job of maintaining contact with all parts of the leaf, despite the irregular shapes of the lost areas. Only one remote point has browned and curled because of the cutter activity. Given the types of damage that can be inflicted upon a leaf, it makes sense that there would be several routes available for maintaining contact with all cells in the leaf.

The Moonseed is the only one of its kind in the immediate area. There aren’t even any other deciduous species nearby. A searching bee, having identified this as a desirable plant, would have made many return trips for additional leaf material. Had there been more plants, the loss of leaf area would have been spread among the population without any harm to any of the plants. If there had been more bees, damage to the plant could have been greater. The instinct to cut large circular areas from the leaves may actually help the plant avoid being completely stripped of leaves. The bee stops cutting when the leaf area no longer allows the proper sized piece to be cut and the plant is left with enough leaf area to survive. It may look a mess, but at least it will be around to try again next year.


  1. Hi Steve...at first I thought you was going to say there was an insect that took that big of a bit..whew I glad it is small and only makes that circle shape a little at a time!!
    Hope the little tree survives!!

  2. Hi, grammie g. If something had been taking those chunks out in a single bite, I would have been pretty nervous about getting that close for pictures.