Moreton Bay Figs in New Zealand

Further to John Swarbrick’s article in the last newsletter, I thought members would be interested in what we learned about the species in New Zealand early last year.

Older parks in New Zealand have some magnificent specimens of these trees. As John pointed out, pollination of figs is done by tiny wasps, with each fig species having a symbiotic relationship with its own pollinating wasp species. In the absence of their particular wasp (Pleistodontes froggatti), the New Zealand specimens of Moreton Bay fig were sterile. They produced “fruits”, but the fruits contained no seeds.

However, the wasp arrived in New Zealand in 1993, moving the New Zealand Moreton Bay figs into a whole new phase. They are now able to produce viable seed, and little seedlings are turning up as epiphytes on both introduced and native tree species.

How did the insects get there? They may have blown in on the wind. Many insects from Australia arrive in NZ every year. Butterflies, in particular, attract attention when they do. P. froggatti have it tougher, because adult females live for only three days. Winds strong enough to get them to NZ do occur every year, but it has taken more than a hundred years for Australian wasps to colonise the New Zealand Moreton Bay figs, so it can’t have been happening very often. Wasps in suitable readiness for egg-laying may have been turning up, from time to time, for many thousands of years, but like so many displaced insects they would have simply failed to breed because they couldn’t find a suitable host plant. Human introduction of their host tree has now enabled the insect to increase its range to New Zealand.

Moreton Bay figs are very large, vigorous, and fast-growing plants which eventually strangle their hosts. It will be interesting to see what effect they have, in the future, on the native flora. Alas, they may not be good news for New Zealand’s beleaguered remnants of native forest.

(Article by Patricia Gardner)