Relative importance of weather and density dependence on the dispersal and on-plant activity of the predator Orius minutus

The present study evaluated the relative effects of abiotic (weather: temperature, wind speed, and rain) and biotic (intra- and intertrophic density dependence: densities of conspecifics, prey per predator individual and leaves on plants) factors on the dispersal and on-plant activity (foraging and oviposition) of the predatory bug, Orius minutus, under seminatural field conditions. Experiments were conducted at plots, each comprising 25 potted azuki bean plants, placed symmetrically in concentric circles, in 1998 and 1999. At the central pot within each plot, 5 marked females of O, minutus (with a male in 1998) were released, and their location and activity were recorded hourly up to 24 h. A total of 78 individuals were released. Stepwise multiple logistic regression was used to select among weather, density dependence, and time variables. Hourly dispersal probability of individuals was positively correlated with temperature and negatively with time since release and with prey density per individual O. minutus. Hourly probability of individuals being active was positively correlated with temperature and negatively with number of leaves of visited plants and conspecific density per leaf. Between-year difference was observed in the probability of individuals being active, which was higher in 1998 than in 1999, probably generated by hunger and higher age. By contrast, diffusion rate was estimated to be lower in 1998, suggesting a trade-off between foraging/oviposition and dispersal by flight. The results indicate that dispersal is affected by temperature and intra-/intertrophic-level density dependence within and between trophic levels, as are foraging/oviposition. The importance of incorporating both abiotic and biotic factors should be stressed when modeling predator-prey metapopulation dynamics on a greenhouse scale.