Nectar quality affects ant aggressiveness and biotic defense provided to plants

Abstract

Ant–plant mutualisms are useful models for investigating how plant traits mediate interspecific interactions. As plant‐derived resources are essential components of ant diets, plants that offer more nutritious food to ants should be better defended in return, as a result of more aggressive behavior toward natural enemies. We tested this hypothesis in a field experiment by adding artificial nectaries to individuals of the species Vochysia elliptica (Vochysiaceae). Ants were offered one of four liquid foods of different nutritional quality: amino acids, sugar, sugar + amino acids, and water (control). We used live termites (Nasutitermes coxipoensis) as herbivore competitors and observed ant behavior toward them. In 88 hr of observations, we recorded 1,009 interactions with artificial nectaries involving 1,923 individual ants of 26 species. We recorded 381 encounters between ants and termites, of which 38% led to attack. Sixty‐one percent of these attacks led to termite exclusion from the plants. Recruitment and patrolling were highest when ants fed upon nectaries providing sugar + amino acids, the most nutritious food. This increase in recruitment and patrolling led to higher encounter rates between ants and termites, more frequent attacks, and faster and more complete termite removal. Our results are consistent with the hypothesis that plant biotic defense is mediated by resource quality. We highlight the importance of qualitative differences in nectar composition for the outcome of ant–plant interactions. Abstract in Portuguese is available with online material.

Optimal Defense Theory in an ant–plant mutualism: Extrafloral nectar as an induced defence is maximized in the most valuable plant structures

“…We can also predict that the extrafloral nectar produced on reproductive structures will be more attractive than that produced on vegetative structures, resulting in greater attraction of ants. Studies have shown that variation in extrafloral nectar production directly influences the ant community and ant foraging patterns (Bixenmann, Coley, & Kursar, 2011; Lange, Calixto, & Del‐Claro, 2017; Pacelhe, Costa, Bronstein, Mello, & Neves, 2019). Higher volumes of extrafloral nectar production attract more ants and can increase ant aggressiveness, resulting in improved plant defence (Falcão, Dáttilo, & Izzo, 2014; Pacelhe et al., 2019).…”

“…For instance, Pacelhe et al. (2019) showed that the predatory activity of ants was higher on plants augmented with artifical extrafloral nectar composed of sugar and amino acids than in plants augmented with only sugar or amino acids or water. Thus, these studies show that more concentrated and nutritive extrafloral nectar influences ant foraging patterns.…”

“…Higher volumes of extrafloral nectar production attract more ants and can increase ant aggressiveness, resulting in improved plant defence (Falcão, Dáttilo, & Izzo, 2014;Pacelhe et al, 2019). For instance, Pacelhe et al (2019) showed that the predatory activity of ants was higher on plants augmented with artifical extrafloral nectar composed of sugar and amino acids than in plants augmented with only sugar or amino acids or water. Thus, these studies show that more concentrated and nutritive extrafloral nectar influences ant foraging patterns.…”

New Tools for Conservation Biological Control: Testing Ant-Attracting Artificial Nectaries to Employ Ants as Plant Defenders

“…Inspired by EFNs, ANs are manipulative tools designed to increase ant activity on trees by dispensing a liquid made of water and sugar to attract ants. Although a few studies have already tested the use of ANs or other food sources to attain agroecological benefits (e.g., [20,21,[97][98][99][100]), none of them have studied ant effectiveness in defending plants, focusing instead on distracting ants from mutualistic sap feeders. Thus, the aim of our study was to evaluate both the functionality of ANs and the impact of different levels of ant activity on arboreal arthropodofauna, plant health and fruit production.…”

Ongoing ecological and evolutionary consequences by the presence of transgenes in a wild cotton population

“…We identified eight species of ants harvesting EFN (Table 2 ), but with distinctive communities as a function of the plant genotype. This result suggests that the change in quantity, and possibly the composition and quality of EFN, can influence the ant community associated with G. hirsutum 39 – 41 .…”