ISBN: 9022005909 9789022005903

Category: Technology & Engineering / Agriculture / General

Page count: 228

The predator-prey interaction (between predacious mite and fruit-tree red spider mite) in these models, which closely approximates the field situation, is based on a detailed analysis of the predation process. This predator-prey interaction is very complex. Five developmental stages of the prey (larva, protonymph, deutonymph, adult male and female), and four developmental stages of the predator (protonymph, deutonymph, adult male and female) are involved. The attractiveness of the different stages of the prey varies and depends partly on the satiation level of the predator. For example, the adult female predator (the most voracious stage) shows a strong preference for the younger stages of the prey, but 'hungry' predators are much less selective. The rate of ingestion and the utilization of a killed prey also depends on the satiation level of the predator. Fransz's detailed analysis of the predation process in the system two-spotted spider mite and predacious mite and the explanatory models he developed for this process showed that a simple system (one standardized predator and a constant number of preys) reaches an equilibrium within a few hours. Hence the degree of filling of the gut of the predator oscillates with a small amplitude, at a level depending on predator and prey density and on the temperature of the system. This enables the complex predation process to be incorporated in a model for a population of higher order by simply expressing relative predation rate and prey utilization as functions of temperature and state of the predator. The satiation level of the predator can be quantified visually, because well-fed predators are dark, while hungry predators are whitish and transparent. A colour scale has been developed which relates the behaviour of the predator expressed in success ratio (number of successful encounters to the total number of encounters) to the quantity of leaf and animal pigments in the predator, which together constitutes its colour.