The nature and effectiveness of antipredatory defences can be evaluated by measuring the efficiency with which predators detect, pursue and subdue prey. The most effective defences of the prey is that used during the phase of predation in which efficiency of the predator is lowest.
The present study was confined to soil protection in an area of pasture. Initially, it was important to survey the area, establish which predators formed the dominant elements in the community and compare the efficiency of the proposed methods of observation. It was also necessary to decide upon suitable prey stages to utilise as baits in this study.
Prey defences have long interested biologists due to the extraordinary diversity of ways in which animals reduce the impact of predation. Endler (1988) categorised defences by their effectiveness in interrupting the behavioural sequence of a foraging predator through at least five stages - prey detection, identification, approach, subjugation and consumption.
Insects are potentially very vurnerable when in one of the immobile stages in the life cycle, i.e. eggs. Diapausing (overwintering) larvae and adults and pupae. These stages are found in a wide variety of species and it may be postulated that one reason for so many of these occurring in the soil is defence against predation. The assumption is that underground predation is more difficult and less common. Eggs can be laid in the soil at different depths, slugs for example, are able to lay eggs at 25 cm or more below ground and insect larvae may also pupate at different depths. The placement of resting stages in the soil requires the expenditure of energy, which may be presumed to increase with increasing depth. This expenditure would only be justified if depth was an important parameter in the protection of prey.
The effects on predator - prey interaction on prey buried at different depths is a major part of the present studies. Laboratory and field work have been carried out to determine : (1) how quickly predators find prey at different depths, (2) how rapidly the prey disappear (survival time of the prey at each depth), (3) which predators are active at each depth, (4) and the rate of predation at each depth. Superimposed upon these studies are the influences of seasonal and diurnal changes on predator activity.
Finally, a very important practical factor influencing predation in the soil is the impact of using insecticides. Without such data, there is no possibility of developing integrated pest management systems, and the effect of soil insecticides was incorporated into this study.
The research programme centred around four techniques: the use of pitfall traps, the rhizotron, laboratory experiments and time lapse cinematography to record predator - prey interaction. These were employed in parallel to observe how predator use a given environment most efficiently and how predatory success is influenced by time (seasonal changes) and place (different depth).
Table 1. The Proportion of invertebrate pests with resting stagaes in the soil (Gratwick, 1992)
Pest No. of % Below ground
Groups species cited Eggs Pupae Overwintering
