Cuckoo wasps (Hymenoptera: Chrysididae) as overlooked hosts of pollinator pathogens: Environmental context of interspecific transmission

Pollinator decline is strongly influenced by the spread of pathogens
across species, yet most research has focused on honey bees and a narrow
range of managed or wild pollinators. Cuckoo wasps (Hymenoptera:
Chrysididae), a diverse family of cleptoparasitic and parasitoid insects,
remain unstudied in this context despite their dual role as floral
visitors and nest parasites of solitary bees and wasps. This study
investigated whether cuckoo wasps could host bee-associated pathogens,
including viruses, microsporidia and trypanosomatids. Specimens were
collected at two Italian sites with contrasting environmental conditions
and analysed individually using quantitative PCR. In total, 343
hymenopterans were screened, including 84 cuckoo wasps representing 21
species. All pathogens except Crithidia mellificae were detected. Pathogen
prevalence and abundance varied significantly between sites, with higher
values of deformed wing virus (DWV) and C. bombi at the montane site, and
greater prevalence of Nosema ceranae and acute bee paralysis virus (ABPV)
at the lowland site, indicating strong environmental influences. Cuckoo
wasps generally showed lower DWV prevalence than wild bees but higher
prevalence of C. bombi and black queen cell virus (BQCV). Strikingly,
host–parasite pairs such as Chrysis rufitarsis and Hoplitis laevifrons
shared nearly the full pathogen set, suggesting direct transmission
through parasitic interactions in addition to environmental and floral
pathways. The obtained findings provide the first evidence that cuckoo
wasps host a broad range of pollinator pathogens. By linking floral and
nest-based transmission routes, cuckoo wasps may play a pivotal ecological
role within pathogen networks. These results highlighted the need to
include parasitic taxa in pathogen surveillance to better understand
pollinator health and ecosystem resilience.