The shapes of plant leaves are very diverse, yet their ecological function is largely unknown. Reports of the effects of leaf shapes on biological interactions such as herbivores are particularly sparse, in part because herbivores rarely rely on leaf shapes for host selection.
On September 2, 2019, Nature Plants published a research paper online titled Leaf Shape Deters Plant Processing by An Herbivorous Weevil. The study shows for the first time that leaf shapes have a physical deterrent to herbivores, so leaf shapes may be an important but overlooked influence on the interaction between plants and herbivores.
A special species of leaf-curling weevil (apoderus praecellens) inhabits plants of the genus Coriander in the family Lipaceae, whose females process the entire leaves into curled leaves for larval food and habitat when laying eggs (see image below). However, in the genus I. umbrosus var. The hakusanensis plant can disrupt its processes because it has deeply lobed leaves of different traits. But is it the difference in leaf shape that causes the leaf-curling weevil to not inhabit and lay eggs on its plants?
The study shows that under natural and laboratory conditions, female weevils are relative to i. umbrosus will give preference to i. Trichocarpus, the morphology of the plant without deep fissures in the leaves. In addition, the study showed that the nutritional properties of the leaves did not explain this preference, as weevil larvae developed well on both host plants.
Comparison of leaf morphology of i. umbrosus (left) and i. trichocarpus (right).
Select experiments test female weevil preferences for both plants
The study further modified the i. Trichocarpus leaves to mimic i. The shape of the umbrosus leaves also prevents the weevil from curling the leaves. Therefore, the study shows that leaf shape can prevent herbivorous insects from handling the leaves. In addition, some non-leaf processing insects also use leaf shapes for host identification after landing. Given the ubiquity of insects that manipulate leaves or identify leaf shapes by palpation, different leaf shapes can function in a variety of ways in the context of biological interactions.
Effect of lobes on female preference