Ingestion of Microplastic Fibres, But Not Microplastic Beads, Impacts Growth Rates in the Tropical House Cricket Gryllodes Sigillatus

Abstract

Microplastic is a growing concern as an environmental contaminant as it is ubiquitous in our ecosystems. Microplastics are present in terrestrial environments, yet the majority of studies have focused on the adverse effects of microplastics on aquatic biota. We hypothesized that microplastic ingestion by a terrestrial insect would have localized effects on gut health and nutrient absorption, such that prolonged dietary microplastic exposure would impact growth rate and adult body size. We further hypothesized that plastic form (fibres vs. beads) would influence these effects because of the nature of gut-plastic interactions. Freshly hatched tropical house crickets (Gryllodes sigillatus) were fed a standard diet containing different concentrations of either fluorescent polyethylene microplastic beads (75–105 μm), or untreated polyethylene terephthalate microfibers (< 5 mm) until they died or reached adulthood (approximately 8 weeks). Weight and body length were measured weekly and microplastic ingestion was confirmed through fluorescence microscopy and visual inspection of the frass. While, to our surprise, we found no effect of polyethylene bead ingestion on growth rate or final body size of G. sigillatus, females experienced a reduction in size and weight when fed high concentrations of polyethylene terephthalate microfibers. These results suggest that high concentrations of polyethylene beads of the 100 μm size range can pass through the cricket gut without a substantial negative effect on their growth and development time, but high concentrations of polyethylene terephthalate microfibers cannot. Although we report the negative effects of microplastic ingestion on the growth of G. sigillatus, it remains uncertain what threats microplastics pose to terrestrial insects.

Characterizing microplastic ingestion, transformation, and excretion in insects using fluorescent plastics

“…This approach is generally inexpensive and highly reproducible, and we believe it can be of great use to researchers interested in the effects of the animal digestive system on ingested plastics (transformation), tracking dosage of ingested plastics, and characterizing the effects of a given dose of plastic on animal physiology and fitness. Fudlosid et al (2022) found that crickets would ingest the same MP beads as those used here and noted that plastic was excreted, but the amount of plastic present in the gut and frass was not quantified. We first examined the segmenting and digestion of the foregut, midgut, and hindgut (Figure 1B) in the crickets to measure whether plastic was present and, if so, how much.…”

“…Fudlosid et al (2022) found that crickets would ingest the same MP beads as those used here and noted that plastic was excreted, but the amount of plastic present in the gut and frass was not quantified. We first examined the segmenting and digestion of the foregut, midgut, and hindgut (Figure 1B) in the crickets to measure whether plastic was present and, if so, how much.…”

“…Commercially available MPs with a fluorescent label bound to them during manufacturing have also been used to track MPs in the digestive tract. Which then can be used analyze MP effects on organisms under laboratory conditions in terrestrial and aquatic species (Al-Jaibachi et al, 2018; Dawson et al, 2018; Fudlosid et al, 2022; Hasegawa and Nakaoka, 2021; Mazurais et al, 2015; Watts et al, 2014). Despite the various methods available, simple and reproducible methods have yet to coalesce for tracking, quantifying, and characterizing plastic particles within animal samples (Lusher et al, 2017).…”

The Fate of Microplastics Ingested by Gryllodes sigillatus

“…The diet of some Orthoptera consists of grasses and a mix of many other perennial plants, but the diversity of the food requires grinding down the plant matter (Joern, 1979). Of the group, crickets have been used in several recent studies of MP effects on insect fitness and have been shown to ingest MPs in a laboratory setting readily (Fudlosid et al, 2022;Helmberger et al, 2022;Lu et al, 2020). While the effects of plastics on crickets are increasingly understood, less is known about how the environment of the cricket gut may influence plastics.…”

“…As cricket's guts have a hardened proventriculus that contains strong grinding teeth-like structures, crickets may be able to degrade MPs physically. The cricket species Gryllodes sigillatus has been found to readily ingest MPs mixed into their feed, which makes them a great model species to investigate MP breakdown in crickets (Fudlosid et al, 2022;Allison et al (personal communication)). Thus far, only a single study has employed methods used specifically to measure MP breakdown in terrestrial insects.…”