Friday, January 19, 2018

Could the African tulip tree Spathodea campanulata be insectivorous?

Trees are not known to feed on insects, but some flowers are known to poison and kill the insects that take their pollen. The African tulip tree, Spathodea campanulata is a tree with insect-killing flowers. Their victims are pollen-collecting stingless bees.   

The theory proposed to explain this behaviour is that the African tulip tree has evolved to favour pollination by birds. Birds visit the flowers to take the sweet nectar at the base of the corolla cup. In the process, their backs get dusted with pollen, which they carry to the next flower. To reserve the pollen for the birds, the pollen contains a poison to deter insects.

A neat theory. but unsupported by facts.

The bees get killed, but new bees are born every day and they keep coming and getting killed. The deterrent does not deter.   

Birds peck a hole at the bottom of the flower and taking the nectar without being dusted with pollen.

Other insects, especially ants, visit the flower for the sweet nectar, and die within the flower because the nectar is poisonous.

How does the poison work? It is a nerve poison. Crawling insects that come into contact with the nectar lose control of their limbs and struggle to crawl out. The flower is big, and the poison takes effect in less than 30 seconds. Before a poisoned insect can crawl to the mouth of the flower, it slips and falls  into the pool of nectar at the base of the flower where it is immobilized instantly.  Bees that come into contact with the pollen presumably fall into the flower when they lose control of their wings. 

The bodies of the insects are retained in the fluid at the base of the corolla for up to four days before the corolla is shed.What happens during these four days? Are there  nutrients from the insects that the corolla can absorb and passes on to the tree before it is shed? Is the corolla a temporary digestive organ?

This work is published in the UTAR Agriculture Science Journal Volume 3 (Nov 1917 that readers can access by Google search. 

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