Golden rain tree, Koelreuteria paniculata, is a beautiful ornamental tree widely planted in landscapes throughout North America. It withstands a variety of growing conditions and soil types. Its ornamental value comes from large clusters of bright yellow flowers displayed from summer into fall. In autumn the flowers produce interesting bunches of showy, papery seedpods. Seedpods are reddish-purple when developing and turn brown as they mature. Several dark brown seeds are produced within each pod. Legions of seeds rain to earth beneath the golden rain tree in autumn. Our southern and gulf-coast states are home to several native plants belonging to the golden rain tree family of plants, the Sapindaceae, commonly called soapberries.
A striking insect called the red-shouldered bug or golden rain tree bug has evolved to use the seeds of soapberries as food. Golden rain tree bug is a "true" bug identified by its sucking mouthparts, young that are called nymphs, and half-leathery, half-membranous front wings. Jadera belongs to the clan of true bugs known as scentless plant bugs or Rhopalidae. We met other rhopalids in previous episodes including boxelder bugs and curious Niesthrea lousianica, the eater of mallows. The introduction of golden rain tree to our country provided an excellent opportunity for the red-shouldered bug to try Asian cuisine. Golden rain tree is now one of the favored foods of this bug throughout our country. This summer was one of record warmth throughout the region and rain trees including those on the campus of the University of Maryland produced seeds by the bazillions.
As I passed a golden rain tree last week, I observed dozens of red and black bugs milling about on the ground, scrambling up trees, and basking on sidewalks. While hordes of bugs were a source of delight for me, so many bugs in one place unnerved some students who quickly moved away. While the weather remains warm, these beautiful red and black insects will mate, lay eggs, and feed on the bounty of the rain tree. Using their beak nymphs and adults pierce the tough seed coat and probe the nutritious meat of the seed. Digestive enzymes pumped into the seed break down proteins, fats, and carbohydrates. Once liquefied, these nutrients are sucked up the beak and into the gut of the bug where they are converted to proteins used for growth and reproduction or broken down to supply the energy for all the running about and mating that occupies the time of these bugs. Adult golden rain tree bugs use this rich source of food to fatten-up in preparation for winter. The rain tree surprise begins when the weather finally turns cold and the bugs seek shelter. In the wild, shelter might be a fallen log, pile of branches and leaves, or rocky outcropping. In their new urban home, winter shelter for the golden rain tree bug might be an instructional building, a nearby dormitory, or maybe a home. After dealing with stink bugs for the past month, if you have a golden rain tree in your yard, this exotic plant may hold one more surprise.
We thank Dr. Shrewsbury for providing the inspiration for this Bug of the Week. To learn more about the golden rain tree bug, please visit the following web site.