Jasmine flowers trap insects
THE New Zealand jasmine Parsonsia heterophylla (family Apocynaceae) is endemic to New Zealand.
It is a climbing, branching liana vine growing to 10m tall. It occurs in wet lowland forests throughout New Zealand’s three main islands, in open habitats including forest margins.
The small creamywhite flowers are 620mm long, and appear profusely in spring and then intermittently in summer and autumn. They have a strong fragrant perfume that attracts moths, flies and Hymenoptera, which assist in pollination.
In his 2016 book Biogeography and evolution in New Zealand,
Dr Michael Heads notes that native flies including Dilophus sp. (family Bibionidae) frequently become trapped in the flowers. While visiting the flowers, the flies catch their legs in the Vshaped gap formed by the anther tails and cannot escape.
The flowers also contain snappedoff legs of flies that have broken away. He cites an example of a small moth and a small lycaenid butterfly (trapped by its proboscis) by
P. heterophylla in Wellington, and also small Taiwanese lycaenid butterflies trapped similarly in Taiwan in
P. alboflavescens, native to Taiwan. Various other
Parsonsia species outside New Zealand also trap insects in this way.
Heads concludes that while the phenomenon may have consequences or implications, including reduced pollination, those are not the cause of the relationship. That is because the relationship is an epiphenomenon, resulting from prior trends in stamen structure on the one hand, and insect leg structure on the other.
Plate tectonics and the present natural distribution of Parsonsia species, which all trap insects, indicate that this secondary effect of insectivorous pollination has happened for millions of years, from the midCretaceous period at least.
The photographs show an example of the epiphenomenon between Parsonsia heterophylla flowers and a trapped native acalypterate fly photographed recently in Dunedin Botanic Garden.