Pollinating fig trees

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In a previous column it was reported that the banyan tree is an East Indian fig tree native to India and Pakistan.

In India, the banyan tree is considered by some to be sacred, and people are reluctant to chop them down due to their religious significance. The banyan tree is one of the more than 800 species of fig trees.

In many parts of the world where fig trees grow, the fig is one of the most popular food items in the forest for wildlife. Most species of fig trees are pollinated by its own special species of fig wasp that can breed only inside a fig of that species of tree.

The fig wasp is no bigger than a sesame seed, but the huge banyan tree would not exist without this tiny wasp. This type of relationship, where two species specifically need each other in order to survive, is termed obligate mutualism.

The fig emits an aroma that attracts the female wasp of the correct species. The female wasp, usually ladden with pollen, will crawl through a tiny opening in the unripe fig, lay its eggs, and then die. In the process, the female wasp can fertilize some of the fig female flower parts that are enclosed within the fig.

The wasp's reproductive cycle involves the formation of a gall that destroys part of the fig. However, viable seeds, resulting from the fertilization process, can develop in the rest of the fig. The eggs hatch and the larvae feed on fig tissue before maturing into adult wasps that mate while still inside the fig.

The inseminated females then start a journey to leave the fig through a tunnel chewed in the fig by the males. During this journey out of the fig, the female wasp will usually brush up against male floral parts inside the fig and pick up banyan tree pollen. The female can then carry this pollen to another fig plant of the correct species and the cycle starts all over again.



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