An insidious pest the size of a sesame seed could destroy some of Brisbane's urban oases if it makes its way to the east coast, experts warn. The polyphagous shot-hole borer, just two millimetres long, has already decimated 4,800 trees in Perth. Urban greens like Brisbane's New Farm Park could be a target for the beetle due to its Moreton Bay fig trees which have been identified as having "very high" susceptibility as a host species.