FACTORS INFLUENCING THE CHOICE OF PREDATORY TACTICS IN A WATER BUG, DIPLONYCHUS-INDICUS VENK AND RAO (HETEROPTERA, BELOSTOMATIDAE)

The tropical water bug Diplonychus indicus is a highly versatile predator that alternates quickly from active foraging to ambushing. The influence of hunger level, the presence of prey and environmental complexity on swimming, diving resting and foraging by adult males was investigated at the individual level, in a factorial experiment with three main treatments. There were simple relationships between these factors and the water bug's behaviour, and interactions between these three factors also affected foraging. The general distribution of foraging tactics between active search and ambushing was significantly influenced by the presence of perching sites (vegetation), but not by hunger levels although hungry bugs as well as bugs in the absence of perching sites were significantly more active than well-fed subjects or bugs in the presence of perching sites. In the presence of vegatation, predatory attempts included fewer dives and more attempts from ambush including preliminary orientations. Hunger level, however, did influence the distribution of ambush predatory tactics; the attempts by hungry subjects included more preliminary orientations. Capture efficiency was not affected by hunger level, but it was affected by the presence of perching sites. Under these experimental conditions the bugs appeared to be capable of modifying, to a certain extent, their predatory tactics in relation to the environment. Nevertheless, the choice of a predatory tactic did not appear to be taken on an all or none basis. © 1990 The Association for the Study of Animal Behaviour.