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Defecation in preparation for ecdysis drives microplastic clearance in cricket nymphs
Summary
Crickets naturally clear out microplastics from their gut right before they molt (shed their exoskeleton to grow), mainly by stopping eating and pooping out the plastic-laden waste—not by shedding their gut lining as scientists initially suspected. This matters because crickets and similar insects are food for other animals (and increasingly, humans), so understanding how they get rid of microplastics helps us figure out whether these plastics are likely to build up as they move up the food chain and eventually reach our plates.
Abstract Plastic pollution is widespread in both terrestrial and marine environments, creating significant ecological concerns. Animals that occupy lower trophic levels, like many small insects, can ingest and retain plastics for extended periods before eliminating them. Ecdysis, or moulting, occurs in arthropods during development and facilitates growth, but its role in microplastic (MP) clearance and whether it is impacted by MPs are largely unexplored. We used the cricket Gryllodes sigillatus to examine how and when moulting influences MP clearance in a hemimetabolous species known to ingest and tolerate MPs throughout development. We tested two alternative hypotheses of how moulting influences MP clearance: (1) moulting of the gut lining removes MPs, or (2) cessation of feeding and/or purging frass before ecdysis occurs removes MPs. In doing so, we also provide new evidence that cricket nymphs exhibit a cyclical (cosinor) pattern of frass production associated with ecdysis. We found that the events leading to ecdysis likely act synergistically to clear the gut contents from crickets' digestive tracts, with the slowing and cessation of feeding and the clearance of frass from the digestive tract eliminating most MPs from the cricket's gut before ecdysis. We also observed that the timing of ecdysis and overall frass production remained unaffected by continuous MP ingestion, whereas switching between MP and non‐MP diets caused modest changes in the timing of frass production within an instar. Crickets are known to biofragment MPs into NPs, which, with gut‐clearing, likely allows them to deposit plastic‐laden frass rapidly and reduces the likelihood of upward trophic transfer by reducing MP retention.