27 August 2008
Life on a southern beech
In a paper published in The Coleopterists Bulletin Marris, Emberson and Johnson describe how they collected sections of beech branches from near Oxford, Canterbury, and placed them into rearing containers. After a week numerous beetle specimens were collected in the trap jar, or by hand as branches were manually searched. Underlining the hidden diversity of New Zealand ecosystems, seven different beetle species were collected from one Oxford branch. The most exciting find was of the beetle Metaxina ornata, the only member of the family Metaxinidae, which is unique to New Zealand. This species is rarely collected but was found to be common in their samples. Collections from Kaikoura and Craigieburn gave similar results.
How can such a small and uniform ecosystem like the branch of a beech tree support so many different species? The beetles probably take advantage of the scale insects, harvesting both the honeydew and the scales themselves. Several of the predatory Metaxina larvae were found inside scale tests (shell-like structures surrounding the scale insect), presumably after eating the former occupant. The pink-tinged gut contents of the larvae matched the pink colouration of the scales - smoking gun evidence of predation. Studies like this are fascinating for how they show just how little we know about the natural history of the hidden world of invertebrates.