Bugged by bacteria: Factors influencing Schistocerca locust and grasshopper microbiome composition

Microorganisms are the most diverse and abundant life forms on Earth, vastly outnumbering all other organisms. Among them, the microbiome, a complex community of microorganisms residing within a host, plays a crucial role in shaping physiology, immunity, and behavior. Insects, like microorganisms, are exceptionally diverse, offering a unique perspective on microbiome research distinct from well-studied human and mammalian models. Even though nearly half of all insect species are herbivores, the microbiomes of generalist plant-feeding insects remain underexplored. Grasshoppers and locusts (Orthoptera: Acrididae) represent a dominant group of herbivorous insects thriving in grassland habitats, which cover approximately 40% of terrestrial ecosystems. However, their gut microbiomes are poorly characterized. Locusts species are grasshoppers that exhibit remarkable behavioral plasticity, shifting between two distinct phenotypic phases mediated by changes in rearing density: the gregarious phase, where they form large swarms at high density, and the solitarious phase, where individuals live in isolation. This behavioral transition raises questions about potential microbiome differences and their role in plasticity. Environmental factors such as diet and habitat may also influence microbial diversity. To examine these effects, microbial DNA was sequenced from Schistocerca americana, comparing individuals collected from the field and those reared in a colony. Additionally, microbial DNA from five Schistocerca species was analyzed, revealing diverse microbial communities with distinct species-level differences. Comparisons between isolation-reared and gregarious Schistocerca gregaria highlighted possible microbiome variations linked to phase transitions. These findings shed light on the interplay between microbial diversity, locust behavior, and environmental influences, suggesting microbial contributions to behavioral plasticity.