Tegeticula is one of the two genera of true yucca moths, moths that have evolved into mutual dependency with the yucca plant. It's a textbook example of coevolved obligate mutualism, one that's relatively easy to study because both species remain in one place rather than dispersing over successive generations. The yucca/moth system holds great potential for education and discovery in the field of evolutionary biology.
Why Tegeticula Needs the Yucca Plant
The female yucca moth has a sword-shaped ovipositor that allows it to cut into yucca's floral ovaries so she can deposit her eggs within. Upon hatching, the larvae feed on the developing seeds.
Why the Yucca Needs the Tegeticula
The female yucca moth plays an active, deliberate role in the fertilization of the yucca plant. She collects yucca pollen and brings it to the stigmas, fertilizing the yucca flower in whose ovary she oviposited and ensuring it will produce seeds for her children to eat. But they don't eat all of the seeds; some always survive to plant the next generation of yucca. So the yucca moth's fertilization role benefits the plant more than its feeding habits are a detriment.
The yucca moth and the yucca plant can be said to have "coevolved." They each acted upon the other as a force of natural selection, forcing genetic change upon each other over successive generations.
Because the interaction between moth and plant are of reciprocal benefit to the growth and stability of each other's populations, their relationship is said to be one of mutualism.
If over time two species in a mutualistic relationship develop to the point that they depend on each other for survival, the relationship is said to be one of "obligate mutualism." Today, the yucca moths and the yucca plant are completely dependent on one another. No other insect pollinates the yucca flower other than the yucca moth, and it cannot self-pollinate. And the yucca is the only host plant the yucca moth can live on. Without the yucca, the larval moths starve.