A unique relationship: the yucca and its moth

Yucca moth collecting pollen from the anther of a yucca flower (after Tackey and Gray, 2017) Image source:  Doug Backlund, WildPhotosPhotography.com

By Stefania Papa

The relationship between yucca moth and yucca plant is very interesting and has a long history. George Engelmann in St. Louis made some first observations in 1892 (Engelmann, 1872). From this data, information about their association has grown at an accelerating pace along several lines of investigation. The moth and the plant depend wholly on each other. Their relationship is a particularly important one because neither the yucca or the moth can survive without the other. The moth’s larvae depend on the seeds of the yucca plant for food, and the yucca plant can only be pollinated by the yucca moth (Helzer, 2013).

From March to June almost every year, a moth known as Tegeticulla yuccasella, lured by the irresistible smell of yucca flowers (Yucca filamentosa), emerges from the ground. Yucca moths are one of the oldest moth species. They are generally white, though some have black speckles on them, or they can be completely greyish black.

At night-time, when blooms are fully open, the male and female yucca moths mate inside the yucca bloom. After mating and collecting flower pollen, the female yucca moth leaves the flower and sets out in search of a newly-opened yucca bloom. Once she finds a suitable flower, she lays her eggs inside the ovary of the flower and deposits the pollen she collected from the first blossom. Before she leaves the flower, the yucca moth marks it with a pheromone (a chemical other moths can sense) (Hebert, 2009).  

The scent marker will tell later visitors that they are not the first to reach the flower, and they will lay either fewer eggs than the first moth, or none at all, depending on how many moths have left their scent already. This helps moderate the number of larvae that hatch within each flower, and prevents the plant from aborting the flower altogether, which it would do if too many eggs were laid inside it.

When the eggs hatch, the larvae feed on yucca seeds inside the fruit.  Typically, there are more seeds than the larvae in a particular flower can eat (since the plant aborts flowers that are too heavily laden with eggs).  When the larvae finish eating, they burrow out of the fruit – usually when it rains. They burrow down into the ground to make their cocoon and wait until the next spring, when the whole process plays out again (Helzer, 2013).

We can say that Yucca moths are little angels to the yucca plants they happen to feed on.

References

Engelmann, G. (1872). The flower of Yucca and its fertilization. Bull. Torrey Bot. Club 3: 33.

Helzer, C. (2013). The Yucca and its Moth. In http://blog.nature.org/science/2013/03/21/the-yucca-and-its-moth/

Hebert, J. (2009) Chu: Yucca No Longer and Option for Nuclear Waste. In https://www.sandiegouniontribune.com/sdut-chu-nuclear-030509-2009mar05-story.html

Tackey C, Gray, P.M. (2017). Coevolution of Yuccas and Yucca Moths. WURJ: Health and Natural Sciences | Volume 8 | Issue 1| https://doi.org/10.5206/wurjhns.2017-18.6

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