Factors affecting ambulatory dispersal in the predaceous mite Neoseiulus californicus (Acari : Phytoseiidae)

Experiments conducted in the laboratory showed that different biotic and ab iotic factors affected the ambulatory dispersal behaviour of Neoseiulus cal ifornicus. The experimental set-up comprised dwarf alfalfa (Medicago polymo rpha) infested or unifested by Tetranychus urticae. Temperatures were measu red with thermocouples. Trials were performed at three temperatures, three prey densities, three light intensities, two relative humidities (RHs) and two vegetative states of alfalfa plants, turgid and withered. Deutonymphs w ere the most dispersive followed by young ovipositional females. High tempe ratures (35 degrees C), high light intensities (40 000 lux) and drought-str essed alfalfa increased the dispersal of N. californicus. The availability of food in the environment and high moisture (80% RH) slowed down dispersio n. The main factors which seem to elicit dispersal behaviour are the depriv ation of food and high temperatures which result in an increase in the walk ing speed of the mite. In addition, other factors tested either increase or reduce the ambulatory dispersal of N. californicus. According to our resul ts, individuals could move from ground cover into apple trees before spring . Exp Appl Acarol 23: 235-250 (C) 1999 Kluwer Academic Publishers.