Effects of sublethal attack by a sucking insect, Hyalymenus tarsatus, on Sesbania drummondii seeds:: Impact on some seed traits related to fitness

Developing seeds of Sesbania drummondii are attacked by nymphs and adults of the bug Hyalymenus tarsatus (Heteroptera: Alydidae), which kill some seeds and weaken others. Parasitism by this piercing-sucking insect reduced the resources for the future seedling and affected seed physiology, including dormancy and exudation of allelochemicals of imbibing weds. Seeds attacked by H. tarsatus had reduced mass (20-80% reduction. depending on intensity of attack). Heavy attack led to irregular shape, changes in seed coat color. and disruption of dormancy. While intact seeds did not imbibe during a 48-hour test in water. a high proportion of bug-attacked seeds germinated. from 51 to 94%, depending on intensity of attack. Attack by H. tarsatus also affected accumulation of allelochemicals and their exudation by imbibing seeds, There were no quantitative differences in proanthocyanidin content between exudate, of attacked and unattacked seeds. In contrast. concentrations of total condensed tannins were higher in exudates of attacked seeds on the third day of imbibition. This change may reflect induction of chemical defenses by herbivore attack and/or a mechanism to restore seed coat impermeability. Although difficult to quantify, effects of sublethal attack by this sucking insect on the seed bank are likely to have important consequences for the demography of S. drummondii, a short-lived perennial in habitats where conditions for recruitment are variable and unpredictable among years.