Motion level in Graphosoma lineatum coincides with ontogenetic change in defensive colouration

Crypsis and aposematism are two different approaches to predation avoidance. Theoretically, the chosen strategy depends on the prevailing possibilities and constraints to the animal. Consequently, insects often change strategy between life stages, but a switch in strategy within a life stage is quite uncommon. In the Swedish shieldbug, Graphosoma lineatum L. (Heteroptera: Pentatomidae), there is a colour change from the pre-hibernating to the post-hibernating adults that alters their protective strategy from effective crypsis to aposematism, although both stages are distasteful to predators. The change in colour occurs as there is a shift of seasons, which alters the environmental background. Here, we investigate whether there is a change in behaviour in G. lineatum connected to the change in colouration and protective strategy. We therefore measured the motion levels in the two different colour forms of G. lineatum, both in the field and in a more controlled laboratory set up. Our result clearly shows that there is a change in behaviour connected to the change in colour. Thus, we found that the cryptic pre-hibernation form has a significantly lower motion level than the aposematic post-hibernation form, which is in line with the fact that motion disrupts crypsis, but not aposematism.