Dendrobium Beetle Stethopachys formosa The Destroyer!!!
As The Australian Orchid Nursery is located 75 kilometres south east of Melbourne we have no epiphytic orchids or ferns within 300 kilometres of us. As a result, there are no natural orchid pests such as Dendrobium beetles down here!
Our cold winters don't allow them to survive. It seems they start around Lakes Entrance in far east Victoria and then go all the way to Cape York in north Queensland. I have only seen them in the wild three times. Once at Merimbula on an isolated outcrop of Dendrobium speciosums, once at Brogo NSW, and finally on the Atherton Tableland munching on Dendrobium speciosum pedunculatums.
I would try Diazonon for an instant kill of the grubs, followed by Confidor pills to stop re-infection, then a Carbaryl spray over the leaves and blooms to take out the adults eating.
For those that like using the bigs guns for commercial control there is a PDF below on the subject. Its the online Wiley one.
If you have any tips for helping get rid of Dendrobium beetles, please comment below!
Over on our Facebook, Phil has one piece of advice that I'm sure has 100% effectiveness!
Here are some great links though to make you all experts.
All my orchids(not just dendrobiums) are outside and unprotected, either in the ground or in hanging baskets and they were all attacked by the Beetle, to the extent they were bare sticks and hadn’t flowered for several years. For the past two months, I have been spraying them every two weeks with a Carbaryl solution of 3ml to 500ml water. I give them a good drenching, especially on the stems where the new leaves connect. They are all miraculously coming back, new growth and flowers everywhere. I initially tried spraying once a month with 5ml/500ml but the new growth was still being destroyed so weakened the solution and every two weeks is working beautifully.