Caterpillars lack a resident gut microbiome.

Area of Science:

• Microbial ecology
• Insect biology
• Evolutionary biology

Background:

• Microbial symbionts significantly impact host animals.
• Larval Lepidoptera (caterpillars) are diverse and ecologically important herbivores.
• Evidence for resident gut microbiomes in caterpillars is scarce.

Purpose of the Study:

• To characterize the gut microbiomes of wild caterpillars.
• To determine the functional importance of gut microbes for caterpillar development.
• To investigate factors influencing microbial colonization in caterpillar guts.

Main Methods:

• 16S rRNA gene sequencing and quantitative PCR were used to analyze caterpillar gut microbiomes.
• Gut microbial communities of 124 caterpillar species were assessed.
• Antibiotic treatment was applied to Manduca sexta caterpillars to assess microbial function.

Main Results:

• Caterpillar guts harbored unusually low-density and variable microbial communities.
• Microbial composition in caterpillar guts reflected ingested leaf-associated microbes, indicating transient colonization.
• Antibiotic suppression of gut bacteria did not affect caterpillar weight gain, development, or survival.

Conclusions:

• Caterpillars primarily host transient microbes rather than specific resident symbionts.
• Caterpillar digestive physiology (high pH, simple gut, fast transit) may inhibit microbial colonization.
• Host-encoded digestive and detoxification mechanisms likely make symbionts unnecessary for caterpillar herbivory, suggesting benefits of symbiont independence.