Katja Poveda

Effects of below- and above-ground herbivores on plant growth, flower visitation and seed set

Separate and combined effects of root and leaf herbivores on plant growth, flower visitation and seed set were tested in a factorial experiment using potted mustard, Sinapis arvensis, at an old fallow field. A 50% leaf removal by cabbageworms (Pieris rapae) when the seedlings had their first four leaves reduced plant height and shoot mass, and delayed the onset of flowering. Root herbivory by two wireworms (Agriotes sp.) over the whole experiment changed flower visitation; the number of flower visitors per plant was higher in plants with root herbivores than in plants without root herbivores. Combined leaf and root herbivory affected flowering period, number of fruits per plant and number of seeds per fruit. Plants attacked by leaf and root herbivores had a shorter flowering period and produced fewer fruits per plant than plants with root herbivores only. Although the experimental plants faced major herbivore-induced growth changes, plant reproduction (seed set and weight per plant) was similar in all treatments, documenting their ability to effectively compensate for leaf and root herbivory.

Herbivory-mediated pollinator limitation: negative impacts of induced volatiles on plant–pollinator interactions

Although induced plant responses to herbivory are well studied as mechanisms of resistance, how induction shapes community interactions and ultimately plant fitness is still relatively unknown. Using a wild tomato, Solanum peruvianum, native to the Peruvian Andes, we evaluated the disruption of pollination as a potential ecological cost of induced responses. More specifically, we tested the hypothesis that metabolic changes in herbivore-attacked plants, such as the herbivore-induced emission of volatile organic compounds (VOCs), alter pollinator behavior and consequentially affect plant fitness. We conducted a series of manipulative field experiments to evaluate the role of herbivore-induced vegetative and floral VOC emissions as mechanisms by which herbivory affects pollinator behavior. In field surveys and bioassays in the plants native habitat, we found that real and simulated herbivory (methyl jasmonate application) reduced attractiveness of S. peruvianum flowers to their native pollinators. We show that reduced pollinator preference, not resource limitation due to leaf tissue removal, resulted in reduced seed set. Solitary bee pollinators use floral plant volatiles, emitted in response to herbivory or methyl jasmonate treatment, as cues to avoid inflorescences on damaged plants. This herbivory-induced pollinator limitation can be viewed as a general cost of induced plant responses as well as a specific cost of herbivory-induced volatile emission.

The enemy as ally: herbivore‐induced increase in crop yield

There is increasing global concern over the risk of food shortage and instability, and a concomitant demand for an increase in food production. However, the continuing expansion of agricultural areas threatens natural habitats as well as human and ecosystem health. One option for increasing food production is to maximize yields from existing farmland. Here we demonstrate that larval feeding by the Guatemalan potato moth (Tecia solanivora), considered one of the most economically important potato pests in Latin America, leads to a dramatic increase in potato tuber production. Field-grown potato plants (Solanum tuberosum) in the Colombian Andes attacked by low numbers of potato moth larvae produce a 2.5-fold higher marketable potato yield than undamaged plants. Greenhouse experiments demonstrate that this effect is induced by larval regurgitant, rather than by mechanical tissue damage. Our results indicate that compounds from the foregut of T. solanivora are necessary and sufficient to induce an increased yield in potato. Our study suggests that using (1) herbivore-derived chemical cues and (2) induced compensatory plant responses to herbivory can provide viable new tools to increase per area crop productivity.

Ecological Communities: Plant-mediated interactions between below- and aboveground processes: decomposition, herbivory, parasitism, and pollination

All terrestrial ecosystems are constituted of a belowground and an aboveground subsystem. These subsystems depend on each other, since above the ground primary producers are the main source of organic carbon for the system, whereas below the ground soil organisms are responsible for the breakdown and recycling of organic matter and the mineralization of the nutrients therein (Scheu and Setälä 2002, Wardle 2002, Porazinska et al. 2003). To understand community and ecosystem-level processes it is necessary to study the interactions within and between these subsystems. However, most ecologists have investigated belowground and aboveground communities separately, leaving the “between subsystems” interactions unstudied (but see Wardle 1999, 2002, Bonkowski et al. 2001, Masters et al. 2001, van der Putten et al. 2001, Brown and Gange 2002). Moreover, studies of different types of plant–animal interactions, such as pollination, herbivory, and seed dispersal, have traditionally progressed separately, focusing on just one kind of interaction and ignoring the possible interference with others (Herrera et al. 2002). This leads to an oversimplification of our understanding of plant–animal interactions, as most plants interact simultaneously with a broad spectrum of animals. Aboveground