Multi-camera field monitoring reveals costs of learning for parasitoid foraging behaviour.

Dynamic conditions in nature have led to the evolution of behavioural traits that allow animals to use information on local circumstances and adjust their behaviour accordingly, for example through learning. Although learning can improve foraging efficiency, the learned information can become unreliable as the environment continues to change. This could lead to potential fitness costs when memories holding such unreliable information persist. Indeed, persistent unreliable memory was found to reduce the foraging efficiency of the parasitoid Cotesia glomerata under laboratory conditions. Here, we evaluated the effect of such persistent unreliable memory on the foraging behaviour of C. glomerata in the field. This is a critical step in studies of foraging theory, since animal behaviour evolved under the complex conditions present in nature. Existing methods provide little detail on how parasitoids interact with their environment in the field, therefore we developed a novel multi-camera system that allowed us to trace parasitoid foraging behaviour in detail. With this multi-camera system, we studied how persistent unreliable memory affected the foraging behaviour of C. glomerata when these memories led parasitoids to plants infested with non-host caterpillars in a semi-field set-up. Our results demonstrate that persistent unreliable memory can lead to maladaptive foraging behaviour in C. glomerata under field conditions and increased the likelihood of oviposition in the non-host caterpillar Mamestra brassica. Furthermore, these time- and egg-related costs can be context dependent, since they rely on the plant species used. These results provide us with new insight on how animals use previously obtained information in naturally complex and dynamic foraging situations and confirm that costs and benefits of learning depend on the environment animals forage in. Although behavioural studies of small animals in natural habitats remain challenging, novel methods such as our multi-camera system contribute to understanding the nuances of animal foraging behaviour.