Exploring behavioural plasticity in the nesting biology of Megachile sculpturalis (Hymenoptera: Megachilidae) and its role in invasion success

The success of animal species is shaped by a combination of ecological conditions and behavioural plasticity, with the latter being particularly crucial for the spread of invasive species. Megachile sculpturalis (Apoidea: Megachilidae), an East-Asian solitary bee introduced to France and subsequently spreading across Europe and North America, provides a case study. While its distribution is well-documented, the behavioural traits driving its success remain poorly understood. Our study aimed to explore behavioural patterns associated with its nesting cycle and potential expansion. In 2020, we conducted focal observations of individually marked females nesting in an artificial bee hotel. Daily recordings, based on ethograms, tracked females' activity at the site. We identified key behavioural units related to nesting goals and analysed the frequency and abundance of actions associated with each marked nest. Our results highlighted the significant effort females devote to nest-related actions, with 50-68% of all behaviours focused on nest building, suggesting any strategy of dispersion should be investigated in this context. While a typical nesting sequence was identified, individual variability indicated plastic nesting responses. Notably, females demonstrated a strong tendency to quickly shift their efforts to new nests following closure or abandonment, even provisioning multiple nests simultaneously. This ability to manage several nests at once may be crucial for establishing populations in invaded areas by rapidly expanding nesting efforts across multiple new sites during a single reproductive season. Our findings emphasize the contribution of behavioural studies in understanding reproductive strategies that influence a species' ability to settle in new environments and expand its range.