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Article History

Received: 17 June 2024

Revised: 18 October 2024

Accepted: 23 October 2024

First Online: 8 November 2024

Declarations

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: The authors declare that they have no known competing interests that could influence the work reported in this paper.

: In species where inbreeding occurs, mothers may bias sex allocation towards females to reduce competition among sons for mates (Local Mate Competition/ LMC). Species with female helpers may also favour female bias due to cooperative interactions (Local Resource Enhancement/ LRE). This study uses genetic analysis to explore the causes and consequences of female bias in the silk wasp, <i>Microstigmus rosae.</i> We find that <i>M. rosae</i> exhibits a unique mating system characterised by frequent sibling mating. These results closely align with predictions of partial LMC theory and provide a rare example of LMC in a social Hymenopteran. Such unexpectedly high inbreeding coefficients parallel those found in other eusocial lineages such as gall-forming thrips and ambrosia beetles, prompting discussion of the potentially significant role of inbreeding in the evolution of social group formation.