There are many reasons why insects are the most diverse group of animals on the planet One of them is herbivory. Feeding on plants opens a huge number of opportunities for insects to diversify. There are new food sources to exploit, new evolutionary ways of dealing with the complex mix of chemical compounds that plants use to defend themselves, and new ways to divide up an individual host plant in ways that reduce competition.
One of the most diverse families of plant-feeding flies is the Agromyzidae, or leafminer flies, so-called because the larvae live and feed sheltered in the nutrient-rich layers inside a leaf, leaving a distinctive mine that is visible from the outside. Lyman Museum member Stéphanie Boucher and her colleague Kenji Nishida in Costa Rica have recently published a new paper in the journal ZooKeys that illustrates how finely these little flies can divide up the world.
Stéphanie and Kenji have described two new species in the enormous genus Liriomyza, an ecologically interesting, and sometimes economically important, genus of agromyzid flies. Many agromyzids are host-specific — their larvae will feed only on a single, or a few closely related species of host plant. These two new species were described from the same host plant, Tree Poppy (Bocconia frutescens), a small tropical tree in the poppy family.
Even though both species feed on the same host plant, they have evolved a convenient way of avoiding competition with one another. Liriomyza mystica larvae mine right along the large midvein and the petiole of the leaf, particularly larger and older leaves.
In contrast, the larvae of Liriomyza prompta mine anywhere on the blade of the leaf, usually avoiding the midvein itself. They also seem less picky about the size of the leaf, and will feed on small to large leaves.
Leafminer flies are notoriously difficult to identify to the species level. The differences between adult specimens are very slight. These two new species can be distinguished from one another only by minor size differences in the adult flies, small differences in the male genitalia, and some small distinctions in the larvae. Not easy. On the other hand, the shape and location of the larval mines makes for a much more obvious difference between the two.
These two new species live and feed in the same neighborhood, but it’s very unlikely that they meet up and compete for food or living space. A single leaf may seem small to us, but to these little leafminers, it’s a world that’s big enough for everybody to get along just fine.