Abstract
Strong effects of predator chemical cues on prey are common in aquatic and marine ecosystems, but are thought to be rare in terrestrial systems and specifically for arthropods. For ants, herbivores are hypothesized to eavesdrop on ant chemical communication and thereby avoid predation or confrontation. Here I tested the effect of ant chemical cues on herbivore choice and herbivory. Using Margaridisa sp. flea beetles and leaves from the host tree (Conostegia xalapensis), I performed paired-leaf choice feeding experiments. Coating leaves with crushed ant liquids (Azteca instabilis), exposing leaves to ant patrolling prior to choice tests (A. instabilis and Camponotus textor) and comparing leaves from trees with and without A. instabilis nests resulted in more herbivores and herbivory on control (no ant-treatment) relative to ant-treatment leaves. In contrast to A. instabilis and C. textor, leaves previously patrolled by Solenopsis geminata had no difference in beetle number and damage compared to control leaves. Altering the time A. instabilis patrolled treatment leaves prior to choice tests (0-, 5-, 30-, 90-, 180-min.) revealed treatment effects were only statistically significant after 90- and 180-min. of prior leaf exposure. This study suggests, for two ecologically important and taxonomically diverse genera (Azteca and Camponotus), ant chemical cues have important effects on herbivores and that these effects may be widespread across the ant family. It suggests that the effect of chemical cues on herbivores may only appear after substantial previous ant activity has occurred on plant tissues. Furthermore, it supports the hypothesis that herbivores use ant chemical communication to avoid predation or confrontation with ants.
Highlights
The role of predators limiting herbivores and indirectly benefiting plants has formed an important foundation of ecology [1,2]
Chemical compounds from crushed A. instabilis individuals (Exp. 1), chemicals given off freely by A. instabilis and C. textor (Exp. 2, 4), and leaves collected from trees with active A. instabilis nests all had fewer beetles and less damage than control leaves without chemicals or leaves from trees without ants (Exp. 3)
In contrast to the above results, S. geminata treatment leaves did not differ from control leaves (Fig. 1C,D), which could imply that the herbivorous beetle did not recognize S. geminata semiochemicals as potential threats
Summary
The role of predators limiting herbivores and indirectly benefiting plants has formed an important foundation of ecology [1,2]. Researchers are interested in understanding how predators indirectly benefit plants, whether it is through densitymediated (lethal effects) or trait-mediated (non-lethal) effects on prey (herbivores) [3]. Few studies focus on how ants deter herbivores and it is often assumed that direct density-mediated interactions or aggressive removal of herbivores is enough to explain the effectiveness of ant defenses. Trait-mediated effects may contribute to the success of ant defenses [11,12,13,14], but have received much less attention
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