Yucca Moths

I’m always fascinated by coevolution, and especially by coevolved mutualisms, but in the plant-pollinator world, the tight, specific interactions that have typically characterized coevolution are the exception rather than the rule.  Indeed, most plant-pollinator interactions are generalized to a great extent.

That’s why those few exceptions, the tight specialized interactions, are so interesting.  I’ve written before about Darwin’s moth and the Rediviva bees in Africa; today I thought I’d talk about another classic mutualistic interaction, the Yucca and its moths.

Yucca is a genus of plants in the asparagus family (Asparagaceae) with tough, sharp leaves and distinctive stalks of white flowers. The Yucca is only pollinated by Yucca moths.

Yucca flowers

Yucca flowers

The Yucca moth is a common name for many species in three genera in the family Prodoxidae. Two of the three genera have an obligate mutualism with the Yucca. And to me they are fascinating because they perform what is known as “active pollination”.  Instead of passively distributing pollen grains carried loosely on their bodies, they have specialized mouthparts (I almost wrote “mothparts”, which would not have been so bad in retrospect), to pick up pollen and move it to the stigma.

From left to right: Showing the specialized mouthparts of the moth, the ball of pollinaria (clumps of pollen) carried by the moth to the stigma, and a larva eating developing seeds (source)

From left to right: Showing the specialized mouthparts of the moth, the ball of pollinaria (clumps of pollen) carried by the moth to the stigma, and a larva eating developing seeds (source)

But as usual in nature, the story is a bit more complicated than a simple mutualism. In fact, the interaction between these moths and plants varies from predation to mutualism.

IMG_5961

Yucca moth on a yucca plant in New York

The larvae of the moths feed exclusively on the seeds of the Yucca, but there is a constraint on the number of seeds they can eat because if they eat too many, the Yucca population will decline and, inherently, so will the population of the Yucca moth.  Naturally, there are cheaters on both sides of the game, and it is balanced by selection over time.

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7 thoughts on “Yucca Moths

  1. I love hearing about these specialized interactions. It reminds me a bit of the squash bee. There are a couple of dozen kinds of native yucca whose flowers all look mostly similar to my eye. Do they all need the moth? And I think it is so cool that your photo shows a yucca moth in NY. Were any yuccas native to that area or were they all imported by gardeners? If they were imported, I think it is all kinds of wonderful that the moth got imported, too.

    • I love specialized interactions too! Great questions…I don’t know the answers but I think all Yuccas need moths, and I do think the yuccas were moved north by gardeners. Because the moth larvae hide inside the developing ovaries of the flowers, it seems like it would be easily moved along with the plants, especially if adults were transplanted!

  2. I always thought of the Yucca as a desert plant, there are a lot of them in Texas and New Mexico, but, if asked, I would have said they could not grow as far north as New York! Guess that’s what I get for assuming and my dad always had a comeback for that. He like to say ass-u-me makes an ass out of you and me. And I would have to say it seem it happens that way a lot. If the Yuccas got imported to that area, did they purposefully import the moth too? Do other bees or moths come to the yucca flowers and just not complete the act of pollination but still carry the pollen off with them, or don’t they see those flowers as something that interests them?

    • I was surprised to find them myself! Haha, I like your dad. I think the Yuccas moved north as ornamentals, and I find it likely that the moths moved with them unintentionally. The larvae hang out in the developing ovaries, so if they moved adult plants, they could easily move the moths as well! I don’t know whether other things visit the yucca flowers although I wouldn’t be too surprised if they did, if only for nectar. A great question!

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