Abstract
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.
Highlights
We found that the effect of persistent unreliable memory can depend on the foraging situation, that is, the plant species containing host and non-host caterpillars, and that persistent unreliable memory can stimulate non-host oviposition on the conditioned plant species
In foraging situation 1, where a single Brassica nigra plant was infested with Pieris brassicae host caterpillars and 14 Sinapis arvensis plants were infested with Mamestra brassicae non-host caterpillars, parasitoids with persistent unreliable memory spent more time foraging on the non-host plants
These parasitoids encountered a foraging situation that conflicted with their memory, which led to a higher number of non-host plants visited and more non-host plant visits compared to parasitoids with persistent reliable memory that encountered a congruent foraging situation
Summary
Insect cultures originated from individuals collected in fields of Brussels sprouts near Wageningen. On one side of the tent a single host-infested plant was placed, on the opposite side, we positioned the parasitoid release plant (always an uninfested B. oleracea plant). Foraging situation 1 consisted of 14 non-host-infested S. arvensis plants, a single host-infested B. nigra plant and an uninfested B. oleracea release plant. Foraging situation 2 consisted of 14 non-host-infested B. nigra plants, a single S. arvensis host- infested plant and a B. oleracea release plant (see Figure 1). To ensure that individual C. glomerata females could be recognized during the field trials, parasitoids were given one of 12 colour markings. The parasitoid was transferred to a small mesh cage (Bugdorm type 41,515, 17 × 17 × 17 cm, Megaview Science) with water and honey and kept in a climate cabinet until conditioning the following day. We did not observe signs of increased mortality of C. glomerata due to application of these colour marks
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