Julia Martinez • 2024 McNair Summer Research Symposium • July 8, 2024

Julia Martinez

Class of 2025

Major: Forensic Science (Criminology)

Mentor: Michael Vallor, PhD

St. Mary’s University

Determination of Midgut Protease Activity in Zophobas morio Larvae Fed a

Diet Containing Microplastic Particles

Microplastics (MPs) are pollutants in terrestrial and aquatic ecosystems consisting of particles

from 5 mm to 10 nm in diameter. These small plastic particles persist in the environment; they

are easily ingested by most organisms, and may produce degradation products known to disrupt

endocrine systems. The abundance of MPs all over the planet is so immense and wide-ranging

that many scientists today have begun studying their effect on biological organisms, which is still

not well known. Superworms (Zophobas morio larvae) have been shown to be capable of

breaking down major plastic polymers such as expanded polystyrene foam through both physical

and biochemical mechanisms, but the effect of this degradation on their digestive enzyme

activity has yet to be characterized. This study aimed to measure the effect of ingesting various

microplastics on midgut protease activity in the larvae of Z. morio. The superworms were fed a

standard diet, with some being “laced” with plain nylon, polyester, polyethylene, and

polypropylene microparticles at various concentrations, as well as polystyrene foam. The

protease activities of their midgut tissues were measured using azocasein. The ingestion of

plastics appeared to cause alterations in midgut protease activity, particularly in the nylon,

polypropylene, and polystyrene feedings. The mechanism of these alterations remains to be

determined. Possible effectors include endocrine disruption, inflammation of the gut lining, or

disruption of gut microbiota. Future directions include measuring the protease activities of gut

contents (secreted enzymes), as well as examining specific proteases such as trypsin and

chymotrypsin.

Keywords: microplastics, midgut enzymes, Zophobas morio, environmental pollutants,

plastic waste