the formation of collective silk balls in the spider mite tetranychus urticae koch集体的形成在蜘蛛丝球螨科赫测定.pdf

The Formation of Collective Silk Balls in the Spider Mite Tetranychus urticae Koch 1 1 ´ 2 2 Gwendoline Clotuche *, Anne-Catherine Mailleux , Aina Astudillo Fernandez , Jean-Louis Deneubourg , Claire Detrain2, Thierry Hance1 ´ ´ 1 Earth and Life Institute, Biodiversity Research Centre, Universite catholique de Louvain, Louvain-la-Neuve, Belgium, 2 Unit of Social Ecology, Universite Libre de Bruxelles, Bruxelles, Belgium Abstract Tetranychus urticae is a phytophagous mite that forms colonies of several thousand individuals. These mites construct a common web to protect the colony. When plants become overcrowded and food resources become scarce, individuals gather at the plant apex to form a ball composed of mites and their silk threads. This ball is a structure facilitating group dispersal by wind or animal transport. Until now, no quantitative study had been done on this collective form of migration. This is the first attempt to understand the mechanisms that underlie the emergence and growth of the ball. We studied this collective behaviour under laboratory conditions on standardized infested plants. Our results show that the collective displacement and the formation of balls result from a recruitment process: by depositing silk threads on their way up to the plant apex, mites favour and amplify the recruitment toward the balls. A critical threshold (quorum response) in the cumulative flow of mites must be reached to observe the emergence of a ball. At the beginning of the balls formation, mites form an aggregate. After 24 hou