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Yucca moth and a plant: a partnership for life

Environmental columnist Frances Lamberts is taking a brief hiatus from writing. She has selected some of her favorite columns to republish. This one ran July 11, 2006.
The yucca plant we see along road sides or in yards has a fine candelabra of bell flowers — white lights that “extinguish” toward June’s end, with the season’s task of reproduction and fruit done.
A few fruits can still be seen pendant from the stalk, green, three-lobed capsules that show small “exit” holes. Some of the developing seeds have fed the larvae of the yucca moth, which is the plant’s only pollinator.
The evergreen, perennial yucca shrub, drought resistant and very hardy, had many uses for the Cherokee Indian people. They made soap and medication from its root, baskets, fishing line and clothing from the fiber of its leaves, used the flower as food.
It also exemplifies in a classic manner the type of partnership between plants and their pollinating insects.
The plant cannot survive except through visits from its one, exclusive and “faithful” pollinator whose own survival, in turn, depends on availability and seasonal flowering of the plant.
The moth doesn’t even get nectar or other food for itself when it visits. It seeks a nursery and a small share of fertile seeds, the exclusive food for its young.
Researchers have described the transaction in the journal, Nature.
The moth, upon visiting, cuts into the flower’s ovary and exposits her eggs within. Then “she walks up to the stigma” and unloads a ball of pollen she has brought from another flower, actively stuffing the pollen between stigmas. She is the only insect known to engage in forcible, deliberate pollen delivery and the transactions are governed by a strict “contract.”
The moth must not lay too many eggs, as few germinable seeds would otherwise survive to ensure reproduction for the plant. She must be diligent in tending the flower and bringing pollen. Yuccas tend to shed flowers with many eggs, especially if the flower has received few visits.
In the researchers words, moths that “produce just enough eggs to get by but repeatedly and dependably pollinate the same flower are favored by natural selection. [Those] that overburden a developing fruit with too many eggs, and are slackers when it comes to providing pollination services, are disadvantaged: the flower aborts, the seeds fail to develop, the moth larvae are left without food, and they die.”
By adhering to their contract, moth and plant can both do well and be stable over millions of years.
We could learn a lot from this particular plant-and-pollinator pair, the yucca shrub and yucca moth, about diligence and forswearing greed, foresight and allegiance to those who are to come after us.