State variables, such as body condition, are important predictors of behavioural traits. Depending on the state of an individual, the costs and benefits associated with different behavioural decisions can vary. An individual's state could affect its average behavioural response and also the behavioural repeatability. Moreover, even for the same state, different behavioural strategies may be adaptive depending on the individual's life-stage. Here, we manipulated the body condition in larvae and adults of a holometabolous insect species, Athalia rosae, using starvation. We assessed the effects of starvation on the behavioural traits of post-contact immobility (PCI) and activity levels and tested their repeatability. Our results show state-dependency of behaviour, although the effect varied with life-stage. Starved larvae exhibited shorter PCI duration and higher activity levels, whereas starved adults were less active than non-starved individuals. Moreover, although most behavioural repeatability estimates were significant in both life-stages, we did not find any significant effect of starvation on the estimates. Next, we calculated standardised effect sizes to compare starvation effects across life stages. We found that starvation had a larger and opposite effect in the larval stage than during the adult stage for all behavioural traits. Finally, we conducted microcosm and no-choice bioassay experiments to examine the benefits and costs, respectively, of the behaviour elicited by starvation in the larval stage. We observed that starved larvae located food faster than non-starved larvae but were also attacked sooner by a predator, possibly due to their higher activity levels. Together, our results demonstrate that behavioural state-dependence is a function of the life-stage of an individual. Moreover, the behavioural strategy exhibited can be adaptive for a specific life-stage with respect to certain functions, like foraging, but also carry costs, like risk of predation.

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