Mechanism of the switchover from extensive to area-concentrated search behaviour of the ladybird beetle, Coccinella septempunctata bruckii

Area-concentrated search of predatory coccinellid adults, Coccinella septempunctata bruckii, is considered to be controlled by internal locomotory information, since the area-concentrated search is generated even if aphids are no longer present in the environment. To investigate what kind of cue elicits the switchover from extensive to area-concentrated search behaviour, the duration of area-concentrated search (giving-up time) was measured after each of the following five kinds of feeding stimuli was supplied: (a) contact with an aphid (Myzus persicae), (b) biting an aphid, (c) consumption of an aphid, (d) contact with an agar block of ca 2 × 2 × 2 mm, (e) consumption of an agar-block coated with a droplet of aphid body fluid. Switchover from extensive to area-concentrated search was observed as a response to all feeding stimuli. The cue to elicit the switchover is the contact with a prey rather than the consumption of it. The giving-up time is dependent on the intensity of feeding stimulus since giving-up time varied according to the type of feeding stimulus (d = a < b < e < c). The giving-up time was positively correlated with the duration of feeding on an aphid which represented the size of prey consumed. To test whether giving-up time is determined by the amount or by the size of prey consumed, it was measured after the ladybird beetle had fed first on a large then on a small aphid (Sequence A) and after it had fed first on a small then on a large aphid (Sequence B). Although the beetle consumed the same total amount of aphids in both sequences, the beetle showed the longer giving-up time in Sequence B than in Sequence A. Therefore, it can be concluded that giving-up time is determined by the size of prey most recently consumed rather than hunger level or prey capture rate.