So many longhorns, and still counting…
Pest or supreme art, longhorn beetles (Cerambycidae) impress with their shapes, colours and patterns. With the Dokmai Garden monsoon woodland growing older, and with the Opkhan national park only six km away, new species of longhorn beetles move in.
Unlike the log-eating larvae of staghorn beetles (Lucanidae), the larvae of longhorn beetles feed on living wood. That means a conflict for a monsoon gardener. He wants to see his saplings grow, and fears the sawdust at the bases of his beloved trees, but at the same time he can not but admire the majestic beetles. Some trees are more susceptible than others. ‘Ton pradu’ (Pterocarpus spp, Fabaceae) seem prone to insect attacks, but in reality we have not yet lost a single tree. I had the opportunity of visiting a garden by the Ping river, planted 25 years ago. There were huge Pterocarpus macrocarpus. Somehow, in spite of the larval attacks of longhorns and moths, and subsequent fungal attacks in the galleries, many saplings manage to grow big. For forestry, although the trees stay alive the quality of wood decreases if there are many holes due to the activity of borers. Mild deterrents such as permethrin (originally from Chrysanthemum or Tanacetum plants) can be used.
The Thai entomologist Pisuth Ek-Amnuay states there are nearly 1200 species of this beetle family (Cerambycidae) in Thailand, Laos and adjacent countries. His own collection of 200 species have been illustrated in his eminent book ‘Beetles of Thailand (2008)’.
Below are some pictures of recently recorded longhorn beetles from Dokmai Garden. If you wish to document your own insect fauna, but realize that your photo model is eager to fly away or can not stand still, cool her down in the fridge a couple of minutes. Set your tripod and camera equipment meanwhile, because back under the camera lens you do not have many seconds before she is fit to run around again.
Xylorhiza adusta is reported to feed on Wrightia (Apocynaceae). Its woolly body and superb patterns should intrigue any artist. When disturbed it can make a sound resembling the sound from polishing a glass window. It is native to India, China, Thailand and Indonesia. After this photo session I released this darling.
Aristobia horridula is a feared pest in tropical Asian gardens and forest plantations. The adults are currently seen in Chiang Mai and mechanical killing on sight may reduce tree damage. Coating the bark with permethrin every six weeks during the rainy season is another way to deter the beetles without killing them. They do fly around at daytime, easily recognized by their tufted and long antennae. Another beautiful beetle with tufted antennae is Aristobia approximator.
This beautiful red beetle (Euryphagus lundii) feeds on dipterocarps (Dipterocarpaceae) and is native to India and Southeast Asia. The red dress and long sinful black gloves make me give her the informal English name ‘woman in red’. The black tips of the elytra show that this specimen actually is a female. Like the other two species this beetle is diurnal. I released this specimen too.
The presence of these beetles in healthy forest ecosystems prevents domination of certain tree species, and provides a steady flow of wood falling to the ground, creating a moister and more porous organic-rich soil which in fact benefits the surviving trees. The branches and logs that fall to the ground become reservoirs for a myriad of other life forms. However, I have not seen any natural forest anywhere in Thailand where the logs are allowed to remain on the ground. Man-made fires and firewood hunters are even faster than the termites. At the very summit of Doi Inthanon mountain there is an attempt to leave logs on the ground of biodiversity and educational reasons.
Text & Photo: Eric Danell
(Precipitation report: 35 mm during the early morning on September 14)