Dendrobium Beetles

The best method to control this pest is to ensure your orchid house is sealed preventing this beetle from getting into your shade house. Depending on the design of your orchid house, this is not always possible and it definitely does not help those orchids growing outside. Although this beetle is quite easy to control with most insect sprays, eg. carbaryl, the larvae is very difficult to control as they are usually inside a cane and thus not reachable by non-systemic sprays. Most poisons that are not totally toxic to yourself, your orchids and the environment will not control this pest particularly well. Fortunately, this beetle is fairly easy to see and quite easy to catch and squash (if you are not too squeamish).

The Dendrobium beetle can fly, although adult beetles seldem seem to fly. If threatened, they merely curl up and drop to the ground where they are virtually impossible to locate unless you happen to have a concrete floor. Thus, to catch this beetle, the simplest method is to place a large mouth jar under the beetle and give the beetle a gentle tap. The beetle will curl up and drop off the leaf into the jar.  Be warned however, that even though the adult beetles seldom seem to fly, the younger beetles with pale colouring seem much happier to fly and will regularly fly off on your approach.   To ensure you catch the young pale beetles, you must be fast and tap them quickly before they get the urge to fly.

Once you have your beetle safely in the jar, you can then squash the beetle, or the squeamish can keep a small amount of water in the bottom of the jar. (As well as not seemingly being able to fly, these beetles don’t seem to be able to swim.)   Again, the mature dark adult beetles will not attempt to fly from the bottle, but the younger pale beetles will often attempt to fly from the bottle if it does not contain water, so squash quickly if you are using the squash technique.

If you use the drowning method to kill these pests, it has been pointed out to me that the addition of a little cooking oil to the water in the jar (or using all cooking oil) will result in the beetles drowning almost immediately instead of drowning slowly.   After trying this method, it is indeed a much quicker method, so I would recommend it over straight water.

In summary, always keep a glass jar in your orchid house. (Always keep a lid on the jar, as it prevents mosquitos breeding in the jar.) Always keep an eye out for these destructive pests and use the glass jar when you find them. It will save you a lot of chewed flowers and leaves.