**Background:** Sociability—the tendency to associate with conspecifics—influences access to resources, mating opportunities, and predation risk, and is often linked to fitness. Predicting its evolution requires understanding both direct genetic effects (DGEs) and indirect genetic effects (IGEs), where genes in interaction partners affect the focal individual's phenotype. IGEs can accelerate, retard, or reverse evolutionary change. Despite their importance, estimates of IGEs on sociability are absent. This study uses phenotypic proxies—repeatability (R), repeatable influence (RI), and the interaction coefficient (Ψ)—to gauge the likely importance of DGEs and IGEs for sociability in the gregarious cockroach *Blaptica dubia*.
**Methods:** 48 male and 48 female unmated adult *B. dubia* were tested in two blocks. Each individual was assayed up to three times as a focal and three times as a partner in dyadic trials over 3 weeks. In each trial, a focal individual was placed in a large compartment separated from a same-sex partner by a fine mesh, preventing the partner from imposing proximity. Sociability was scored as the sum of distances from the mesh recorded every 10 min over 80 min (maximum 8 measures per trial). Smaller values indicate higher sociability. Partner body mass was recorded to the nearest 0.01 g. After the third trial, individuals were aggregated into four groups of 21–24 (same sex, same block) with four shelters each. Shelter co-occurrence was recorded 5 times over 21 days to construct social networks. Simple ratio association indices were calculated, and each individual's summed association scores gave its network 'strength'. Repeatability (R) and repeatable influence (RI) were estimated from a generalized linear mixed model (Poisson error, log link) with random effects of focal ID, partner ID, and date, using the QGglmm package to obtain estimates on the original scale. The interaction coefficient Ψ was estimated as the regression coefficient of focal sociability on partner body mass. A bivariate mixed model in MCMCglmm estimated the among-individual correlation between dyadic sociability and network strength.
**Key Results:** 193 observations from 92 individuals were collected. Sociability in dyadic trials correlated strongly with network strength (among-individual correlation mode = −0.878, 95% CI: −0.978 to −0.311), validating the assay. Repeatability of sociability was low: R = 0.080 (ΔAIC with vs. without focal ID = 774). Repeatable influence of partners was also low: RI = 0.053 (ΔAIC with vs. without partner ID = 775). Partner body mass significantly influenced focal sociability, but in opposite directions for the sexes (interaction β = −2.914, SE = 0.686, χ² = 18.053, p < 0.001). Males were more sociable with larger partners (Ψ_male = −0.129, SE = 0.107), while females were more sociable with smaller partners (Ψ_female = 0.071, SE = 0.102). Heavier focal individuals of both sexes were more sociable (β = −1.012, SE = 0.449, χ² = 5.077, p = 0.024). Temperature had no clear effect (β = 0.177, SE = 0.180, χ² = 0.971, p = 0.324).
**Clinical Implications:** This study does not have direct clinical implications. However, cockroach species are sources of zoonoses, and understanding the evolution of aggregation behavior could inform how disease risk to humans may change under selection pressures such as climate change and management strategies. The findings highlight that sociability has limited evolutionary potential via direct genetic effects, but indirect effects through body size could drive sex-specific evolutionary trajectories, potentially influencing population dynamics and disease transmission patterns.