Cesar Rodriguez-Saona, Ph.D.
Research with Dr. Thaler: My research focused on multitrophic interactions involving plants, herbivores, and the natural enemies of herbivores. In general, I investigated the “Ecological Determinants in the Success of Natural Enemies of Herbivores”. Specifically, I studied plant traits that mediate interactions between herbivores and their natural enemies.
My experiments at Dr. Thaler’s lab and at the Field Station (Joker’s Hill) addressed the following questions:
1. Are induced responses in plants affected by multiple species of herbivores? Induced responses are a common phenomenon in plants. However, typically these studies have been conducted with single species of herbivores. I investigated how induced responses to one species of herbivore are influenced by the presence of a second species of herbivore on plants. These responses to multiple species of herbivores may affect the foraging behavior of herbivores, as well as the natural enemies of the herbivores.
The system I selected for my studies consisted of tomato plants, because of their well-documented specificity in response to feeding by different species of herbivores. Two herbivores with different feeding habits: a phloem-sucking insect, the potato aphid Macrosiphum euphorbiae (Fig. 1) and a chewing caterpillar, the beet armyworm Spodoptera exigua (Fig. 2). These two species were chosen because of the potential interactions in plant responses when herbivores with different feeding habits share a common plant. I tested the responses in plants to feeding by single and multiple species of herbivores on the performance and preference of a parasitic wasp, Cotesia marginiventris (Fig. 3), and its host S. exigua.
Potato Aphid (Fig. 1) Beet Armyworm (Fig. 2)
Cotesia marginiventris (Fig. 3)
2. How levels of damage among patches of plants affect the distribution of herbivores and their natural enemies? I conducted field experiments where I manipulated the amount of damaged plants among patches and determined insect colonization on the different patches. Herbivore damage causes plants to induce volatiles that can affect the distribution of herbivores and natural enemies on these plants (Fig. 4). I predicted that plant volatiles in patches with higher number of damaged plants might be more concentrated, which may influence the use of these patches by herbivores and the natural enemies of the herbivores.
At Joker’s Hill, I randomly divided patches of tomato plants (3 plants per patch) into three groups: HIGH damage, where all plants within a patch had been damaged by S. exigua; MEDIUM damage, where 1 plant per patch was damaged; And LOW, where none of the plants within the patch received damage (Fig. 5). I then monitored the colonization of herbivores and natural enemies of herbivores for 2 consecutive weeks.
Volatiles from Damaged Plants Attract Natural Enemies of Herbivores (Fig. 4)
Experiments Conducted at Joker’s Hill Field Station (Fig. 5)