The Disadvantage of Having a Big Mouth: The Relationship between Insect Body Size and Microplastic Ingestion

Plastic pollution is ubiquitous. When plastics enter
natural environments,
they break down into microplastics (MPs; <5 mm), becoming more
accessible to smaller animals. Insects ingesting plastics in the wild
can physically degrade larger MPs into smaller MPs and nanoplastics.
While particle size and body size undoubtedly impact plastic ingestion
and degradation, we have no predictive understanding of how these
factors interact. We studied how a model cricket species (Gryllodes sigillatus) interacts with plastics of differing
sizes throughout a 20-fold change in body mass during growth and development.
We fed crickets differently sized polyethylene MPs to first investigate
whether crickets would avoid MPs when given a choice. We found that
they do not. Instead, they gradually began to consume more of the
plastic diet over time. Crickets would only consume beads when their
mouth size was larger than the MP. While small MPs (e.g., 38 μm)
were more likely to be excreted whole, larger MPs (e.g., 425 μm)
were more extensively biofragmented if ingested. These effects of
insect behavior and body size on the likelihood of plastic ingestion
and the degree to which MPs are degraded have important implications
for how and when we should regulate size classes of plastic particles
entering natural environments.