The Ipomoea species, commonly known as morning glories, are fast-growing, twining vines prevalent in gardens and wild spaces across the globe. Belonging to the Convolvulaceae family, these plants often show invasive tendencies and draw significant attention from herbivores due to their rapid spread and abundance. Various animals consume their foliage, stems, and roots in both cultivated areas and natural ecosystems.
Insect Herbivores of Morning Glories
Insects represent the most specialized and numerous group of animals that consume morning glories, with feeding habits categorized by the specific plant part they target. Leaf-eating insects, or defoliators, cause the most visible damage. Species like the various caterpillars of the Sphingidae moth family actively chew through the foliage, and flea beetles also contribute to defoliation, leaving behind characteristic small, shot-hole-like perforations.
Beyond the visible foliage damage, other insects employ different feeding strategies. Sap-sucking insects, such as aphids and whiteflies, use stylets to pierce the plant’s vascular system, drawing out nutrient-rich phloem sap. This feeding process can weaken the vine and potentially transmit plant viruses, causing further stress to the morning glory. Root and stem borers, though less visible, can cause significant structural damage by tunneling into the underground or woody parts of the plant.
These below-ground pests include various nematodes, which are microscopic roundworms that feed on the roots. They cause galls or swellings that impede the plant’s ability to absorb water and nutrients. Certain insects have developed the ability to overcome the plant’s natural defenses, indicating a long history of co-evolution.
Mammalian Browsers and Opportunistic Eaters
Larger animals, primarily mammals, also feed on morning glories, though their consumption is generally less specialized than that of insects. Opportunistic browsers like rabbits, groundhogs, and deer readily consume the foliage and tender stems of the vine. This browsing behavior often results from local food scarcity, where animals resort to eating less palatable plants when preferred forage is unavailable.
Young morning glory plants or new, soft growth are particularly susceptible to mammalian browsing, as these parts contain lower concentrations of defensive compounds compared to mature leaves. Unlike insects that target specific tissues, mammals typically consume the aerial parts of the plant—the leaves and growing tips—for quick energy and hydration. The seeds, which hold the highest concentration of protective substances, and the tougher root systems are generally avoided by these grazers.
Plant Defenses and How Animals Overcome Them
Morning glories possess chemical defenses, primarily ergoline alkaloids, which are bioactive compounds that deter many generalist herbivores. These alkaloids, including lysergic acid amides (LSA), are concentrated in the seeds, acting as a defense for the plant’s reproductive future. The production of these compounds is often due to a symbiotic relationship with the Periglandula fungus, which lives within the plant tissue and produces the alkaloids.
The leaves and stems also contain these compounds, but usually at lower concentrations than the seeds, which allows for some browsing pressure from larger animals. However, the most successful insect herbivores have developed sophisticated mechanisms to overcome these chemical deterrents. Some specialist insects have evolved highly active enzyme systems, such as cytochrome P450 enzymes, which are capable of detoxifying or breaking down the ergoline alkaloids into less harmful metabolites.
Other insects utilize behavioral strategies, such as rapid digestion, which allows them to absorb necessary nutrients quickly while minimizing the time toxins remain in their system. The presence of these alkaloids also benefits the plant by deterring below-ground threats. The transfer of ergot alkaloids to the roots has been shown to decrease gall formation caused by root-knot nematodes.