Scaling up individual behavior to predict population spread: experiments with microscopic insects

Vincent Calcagno
Université Côte d'Azur, CNRS, INRA, Institut Sophia Agrobiotech, 400 route des Chappes 06903 Sophia Antipolis, France

Understanding how behavioral processes, inter-individual variability and interactions shape the spatial spread and dispersal of animal populations is a major challenge in ecology. Trichogramma parasitic waps are among the smallest insects in the world (less than 500 micrmeters long). They are grown and released by millions in the field to protect crops from insect pests, so that understanding their spatial propagation dynamics is critical to predict performance. I’ll present how a novel experimental system coupled with high-throughput tracking of individual movements by computer vision can give insight into the spatial spread of groups of parasitoid individuals over large temporal (one entire day) and spatial (six meters, ca. 12,000 body lengths) scales in the lab. In particular I’ll show how population spread is well described by heterogeneous diffusion, whereby individuals switch between two states dynamically (active versus sedentary) depending on their encounter with other individuals or with resource items. I’ll also show how these rather complex movement strategies ultimately generate a fairly simple Gaussian spatial distribution of host parasitism around the release point.