On the role of direct sunlight for egg‐laying behaviour: lessons and ideas from the Speckled wood

Braem, Simon [UCL] Van Dyck, Hans [UCL]

1. Butterflies rely on suitable weather conditions for thermoregulation during active behaviour. While non-sunny conditions are known to reduce time spent in active flight, detailed behavioural data on how variable microclimatic conditions affect decision making in specific behavioural contexts (e.g. habitat exploration, dispersal, mating, basking, oviposition) is often lacking. 2. We addressed the influence of direct sunlight on females of the Speckled wood butterfly (Pararge aegeria) that were motivated to oviposit. To test this, we observed gravid butterflies one by one in (1) a cage within a greenhouse, where temperature was kept high all the time, and (2) an outdoor cage under uncontrolled weather conditions. 3. Our results show that butterflies almost exclusively oviposit under direct sunlight. Surprisingly, results were similar in the warm within-greenhouse cage, where activity remained high but oviposition never occurred during fully clouded conditions. 4. These results suggest that ovipositing butterflies require sunlight not only for thermoregulation. We hypothesise that direct sunlight benefits the ovipositing female by exposing more clearly the microclimatic variation of potential oviposition sites in the herbaceous layer of the vegetation. Heliophily during oviposition and pre-oviposition exploration may apply to a range of microclimate-sensitive species, particularly those living in microclimatically heterogeneous habitats. This warrants novel sensory ecological research, which will further improve our understanding of insect functional habitats.