PARENT SESSION
Contributed Oral Session 3: Herbivory: Plant - Herbivore Interaction
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 513 E, Level 5, Palais des congrès de Montréal
Translating behavior into population dynamics in an insect-plant interaction revealed by biological weed control.
McEvoy, Peter*,1, Fitzpatrick, Greg1, 1 Oregon State University, Corvallis, OR, USA
ABSTRACT- We ask how the colonizing and foraging behavior of a phytophagous insect influences the spatial and temporal distribution of the attack rate among heterogeneously distributed host plants, and how this attack distribution in turn affects the equilibrium levels and stability of insect-plant population interactions. We studied a system of interactions revealed by classical biological control involving a flea beetle (Longitarsus jacobaeae ) and its host plant ragwort (Senecio jacobaea ). We experimentally varied the distribution of hosts in the field and measured both the colonizing behavior of the herbivore and the rate of change in host and herbivore populations. The experiment was carried out at multiple temporal scales (within and between years), spatial scales (within and between aggregations of resource patches), and biological scales (from individuals to populations). We found that beetles rapidly redistributed themselves among patches within aggregations so that the number of colonizing beetles increased with the number of hosts per patch (1, 4, 8, 16 hosts per 0.25 m-2 patch) (the area effect); the number of beetles colonizing aggregations of patches decreased with distance from the source of colonists (the distance effect). The redistribution of beetles among patches tended to stabilize the rates of increase in the herbivore population (consistent with the ideal free distribution) and stabilize the rate of decrease in the plant population. These results show for multiple scales of observation that the ragwort flea beetle is an extremely efficient regulator of host abundance, and this in turn may account for its remarkable success as a weed biological control agent. Our study helps fill the gap between studies of behavior and studies of population dynamics in plant-herbivore systems.
Key words: foraging behavior, population dynamics, plant-herbivore interactions