June Phenology Report: Ecological Traps
By Jocelyn LaClair, Seasonal Horticulture & Sales Assistant
In the modern horticultural world, native species often take a backseat to non-native species selected for aesthetics and fast growth. But these choices can have devastating impacts on wildlife that often go unnoticed. Insects rely on specific host plants to develop due to the specific chemicals and nutrients found in the foliage. One might think that closely related but non-native species could support these same insects—but this may not be the case. Instead, these non-native plants may function as “ecological traps.”
In source-sink theory, animals choose high-quality habitats and avoid low-quality habitats. Animals fill up the chosen high-quality habitat, and the leftovers are forced to settle in the low-quality habitat. High-quality habitats that are chosen will increase populations (source), and low-quality habitats that are avoided will decrease populations (sink). This keeps the population relatively stable when high quality habitats are present, because if there is any overflow, they will move to the sink habitat where populations decrease. However, ecological traps occur when there are low-quality habitats that are chosen instead of avoided. Animals use environmental cues to identify what makes a high-quality habitat, and if low-quality habitats demonstrate these same cues, animals may confuse the two. This can lead to extinction. Animals that would have chosen the stable, high-quality habitat, are instead choosing the low-quality habitat where populations decrease. (Battin 2004. Conservation Biology 18(6):1449-1717)
A recent study explored this phenomenon in Promethea moth caterpillars and their host plant, trees in the genus Prunus (Narango & Straley 2025. Ecosphere 16(5):e70274). The genus Prunus is home to hundreds of species, with native ranges scattered across the globe. This study tests 14 of those species, some native to New England and some not, to see if non-native but closely related species can raise caterpillars as well as true natives can. The authors found that Prunus serotina, native Black Cherry, performed the best in terms of survival, fastest growth, and most biomass. Only 8 of 14 species were able to successfully support caterpillars to pupation. Some species with nearby native ranges performed well, but species originating from other continents could not support caterpillars all the way to pupation. On non-native species, caterpillars seemed to be doing fine until they reached their fifth and final instar, or stage of development. Then, survival dropped off drastically, and any caterpillars that did survive were small and weak.
Because Promethea butterflies still choose to lay their eggs on non-native Prunus species, these trees may function as an ecological trap. Some caterpillars may survive, but ultimately these non-native trees contribute to population decline. There are so many things we don’t know about interactions between insects and non-native plants. In the meantime, let’s do something guaranteed to help wildlife—plant native!
Photo: Promethea silkmoth cocoon from a Black Cherry tree in the nursery.
