Turn alternation and the influence of environmental factors on search routes through branched structures by ladybirds (Coccinella septempunctata and Adalia bipunctata).

Turn alternation is a locomotory behaviour wherein an animal makes consecutive turns in opposite directions (left-then-right or right-then-left). It has been suggested that its adaptive function is to maintain locomotion in a relatively constant general direction while negotiating obstacles. Previous work has focussed on the use of turn alternation in prey species in artificial horizontal mazes. In the first study presented here, we tested whether predatory seven-spot ladybirds (Coccinella septempunctata) exhibit turn alternation when repeatedly presented with consecutive choice turning decisions on vertically oriented twigs. Our findings suggest that turn alternation occurs vertically as well as horizontally, on plant structures as well as terrestrially, and in a type of animal (predatory insect) in which turn alternation has received little attention. In the second study presented here, we tested whether characteristics of branched structures explored by two-spot ladybirds (Adalia bipunctata) influence turning decisions. Our findings suggest that ladybirds exhibit preferences for thicker over thinner, straighter over more deviating headings, and higher over lower turning choice options at bifurcations. These exploratory studies indicate that while turn alternation is an observable phenomenon in ladybirds, it is not the only predictor of searching behaviour on branched structures.