Sex-specific survival and absence of Wolbachia-mediated protection during invertebrate iridescent virus 31 infection in Armadillidium vulgare.

Invertebrate Iridescent Virus 31 (IIV-31, or Iridovirus armadillidium1) is a large double-stranded DNA virus that induces iridescence and high mortality in terrestrial isopods. Despite its broad distribution, its pathogenic mechanisms and interactions with host immunity and endosymbionts are poorly understood. We examined the effects of IIV-31 infection on survival, hemocyte concentration and viability, septicemia, and viral load in Armadillidium vulgare, while testing for protective effects of the feminizing endosymbiont Wolbachia (wVulC strain). Virgin adults from asymbiotic (males and females) and Wolbachia-symbiotic (females only) lineages were experimentally infected by needle pricking. Infected individuals exhibited typical iridescence from ~6 days post-infection (dpi), culminating in 100% mortality after 80 days. Wolbachia conferred no significant survival benefit (log-rank test, p = 0.42). However, despite attaining 100% mortality in both sexes by 80 dpi, females exhibited delayed mortality kinetics compared to males (Cox proportional hazards model, p = 0.04). Infected isopods displayed a marked reduction of circulating hemocyte numbers (negative binomial GLMM, p < 0.0001) and elevated septicemia (p = 0.008), with higher septicemia in infected females relative to their controls, but no sex difference in viral load at 30 dpi (p = 0.23). These findings demonstrate that IIV-31 causes reduction of circulating hemocyte counts and opportunistic septicemia, with female-specific tolerance but no Wolbachia-mediated protection, underscoring sexual dimorphism in immune responses as a pivotal factor in isopod-iridovirus dynamics.