Body Size Trade-Offs Underpin Reproductive Success and Thermal Stress Tolerance in an Invasive Pest, the Small Hive...

Body size is an important feature of organisms that correlates strongly with fitness, as it directly or indirectly influences nearly all biological phenomena. The body size of an organism is, in turn, shaped by many biological and physical factors that may not only directly affect the individual but also influence offspring through maternal investment or provisioning and transgenerational mechanisms. Body size differences have widely been observed in adult small hive beetles (Aethina tumida Murray, SHBs), an invasive pest of honey bee colonies; however, little is known about the evolutionary and ecological implications of these variations. We hypothesized that parental body size influences reproductive performance, progeny fitness, and stress tolerance in SHBs. To test this, we paired different adult sizes and sexes of SHBs in rearing containers and compared their reproductive abilities and offspring fitness. We also exposed the progeny beetles to extreme temperatures and measured their thermal tolerance. A clear trade-off emerged: larger beetles generated more offspring with lower fitness, while smaller adults produced fewer but higher-fitness offspring. Additionally, larger SHB females showed greater tolerance to extreme temperatures, while small males were the most vulnerable. This study reveals that parental body size in SHB plays a pivotal role in shaping offspring reproductive traits and thermal stress tolerance. These findings highlight a potential mechanism by which SHB adapts and thrives across diverse and changing environments. Management strategies that exploit these life-history trade-offs could help shift populations toward weaker generations, thereby enhancing long-term control effort.