The digestive system of a cricket pulverizes polyethylene microplastics down to the nanoplastic scale.

Microplastics (MPs; <5 mm) are a growing concern and a poorly understood threat to biota. We used a generalist insect (a cricket; Gryllodes sigillatus) to examine whether individuals would ingest and physically degrade MPs in their food. We fed crickets a range of concentrations (0, 2.5, 5, and 10% w/w) of fluorescent polyethylene MPs mixed into a standard diet and dissected the gut regions to isolate the MPs within. Comparing plastic content and fragment size within gut regions, we sought to identify whether and where crickets can fragment ingested MP particles. Given the digestive tract morphology of this species, we expected that the crickets would both ingest and egest the MPs. We also predicted that the MPs would be fragmented into smaller pieces during this digestive process. We found that G. sigillatus egested much smaller pieces than they ingested, and this fragmentation occurs early in the digestive process of this insect. We found this for both sexes as well as across the range of concentrations of MPs. The degree of plastic breakdown relative to plastic feeding time suggests that the ability to fragment MPs is intrinsic and not altered by how much time crickets have spent eating the plastics. The amount of plastics found in each region of the gut in relation to feeding time also suggests that this size and shape of PE microplastic does not cause any physical blockage in the gut. This lack of evidence for blockage is likely due to plastic breakdown. We found a ∼1000-fold reduction in plastic size occurs during passage through the digestive system, yielding particles very near nanoplastics (NPs; <1 µm), and likely smaller, that are then excreted back into the environment. These findings suggest that generalist insects can act as agents of plastic transformation in their environment if/when encountering MPs.

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

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.

Tests of the positive and functional allometry hypotheses for sexually selected traits in the Jamaican field cricket.

Sexually selected traits, including threat signals, have been shown to scale steeply positively with body size because their exaggeration maximizes honest signalling. However, the functional allometry hypothesis makes the opposite prediction for some weapons: because the biomechanics of force applied in their use may favor relatively smaller size, sexually selected weapons may exhibit negative allometry. Tests of these ideas in insects have largely focused on holometabolous species, whose adult body size is entirely dependent on nutrients acquired during the larval stage. In contrast, hemimetabolous insects may exhibit different patterns of allometry development because they forage throughout development, between successive moults. Here, we tested complementary and competing predictions made by the positive and functional allometry hypotheses, regarding intrasexually selected trait allometry in a hemimetabolous insect, the Jamaican field cricket (Gryllus assimilis). As expected, head width (a dominance and/or combat trait) was more positively allometric than non-sexually selected traits. In contrast, and consistent with the functional allometry hypothesis, mouthparts (weapons) were either isometric or negatively allometric. We also tested whether trait allometry responded to rearing diet by raising males on either a high protein diet or a high carbohydrate diet; we predicted stronger positive allometry under the high protein diet. However, diet did not influence allometry in the predicted manner. Overall, our results support the functional allometry hypothesis regarding sexually selected trait allometry and raise intriguing possibilities for integrating these ideas with recent paradigms for classifying intrasexually selected traits.

Compensatory Abilities of Canola in Response to Swede Midge (Diptera: Cecidomyiidae) Damage.

Swede midge (Contarinia nasturtii Kieffer) is an invasive, economic pest of canola (Brassica napus L.) that threatens production throughout Canada. Swede midge has up to four overlapping generations, placing canola at risk of multiple infestations in the field. The relationship between single and multiple swede midge infestations at different canola stages, and the resulting impacts on yield, are unknown. Laboratory experiments were conducted to evaluate the impact of single and multiple infestations of swede midge on four plant stages of canola: three-leaf, seven-leaf, primary bud, and secondary bud. Previously, the seven-leaf and primary bud stages were considered vulnerable to swede midge, but we determined that the secondary bud stage is also vulnerable. Evidence of compensation by canola in response to herbivory by swede midge was discovered. Compensation occurred mainly through increased production of tertiary racemes and pods and was maximized with exposure of 4.5-6.5 female midges per plant. Although compensation may increase potential yield, it also results in uneven crop maturation resulting in delayed harvest and yield loss. Consequently, to prevent delays in maturation and harvest, insecticides should be applied before these densities are reached.