Noisy beasts
VulcanSpirit
Richard & Alison Brunstrom
Wed 1 May 2013 10:00
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This is one of my favourite NZ insects - a Chorus
Cicada, Amphipsalta zealandica, or kihikihi wawa in Maori, sitting on a
manuka tree next to our tent and making a truly enormous din. These are
middle-sized as cicadas go, about 25mm long with an 80mm wingspan. Having spent
several very boring years as a larva underground in a cell with their hypodermic
mouthparts buried in a plant root to extract the sap the adults hatch in their
hundreds of thousands in early summer, and when the temperature is right
the males 'sing' like anything. In fact the males make two entirely different
sounds, a typical cicada whirring chirping noise made by vibrating a drum-like
membrane at the base of the wings, and a surprisingly loud clicking noise made
by tapping the rigid angle of the wing on the substrate, usually a branch, a
method which I think is restricted to NZ cicadas.
 But being New Zealand, things are not
straightforward. NZ's cicadas have clearly undergone adaptive radiation (as per
Darwin's finches) where a generalist ancestor colonises new land and has an
opportunity to fill a series of vacant ecological niches by producing a whole
array of specialised descendants. There are now 42 species of cicada recognised
here (including, in true NZ style, the world's only alpine cicada), but
where did they come from? When did they arrive? How many times did colonisation
happen? Much lengthy scientific investigation has been undertaken into these
fascinating questions upon which I could now (having swatted up) expound upon at
length, but cutting to the quick molecular biology can now show that
cicadas arrived in NZ twice, both times post-Oligocene ie. in the last 20m
years. Amphipsalta's ancestors came direct from Australia and gave
rise to four current NZ species. But the rest, though also originating in
Australia, share a common ancestor with cicadas in New Caledonia. Either
New Caledonia was colonised from NZ, or vice versa; it is not clear yet which.
Considering the vast length of time that NZ has been isolated (80m years) it is
clear that even with a winged insect like a cicada, two colonisations in 80m
years demonstrates successful dispersal and colonisation to be at the
miracle end of the frequency spectrum! But what a wonderful addition to
the NZ summer they make; I'm glad they made it here,
somehow.
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