Muzzatti, M. J. | bioRxiv Science

bioRxiv2022

Fruitful female fecundity after feeding Gryllodes sigillatus royal jelly

Dietary honey bee royal jelly increases insect growth rates and adult body size. Royal jelly could enhance mass insect production as a dietary supplement, but it is costly to produce. The mechanisms underlying the effects of royal jelly on growth remain unclear, and so it is valuable to understand the effects of royal jelly on a mass reared model species to try and augment body size in a more cost-effective manner. To determine the effect of royal jelly on a cricket species (Gryllodes sigillatus) farmed on mass for human consumption, we ran two experiments. In one experiment we tested the dose-dependent response of Gryllodes sigillatus to royal jelly using a range of diets across 0-30% w/w royal jelly. In another experiment we measured the individual-level life history responses of Gryllodes sigillatus to royal jelly over time by individually rearing freshly-hatched Gryllodes sigillatus on two separate diets: half were fed a commercially available cricket diet, while the other half were fed the same diet mixed with 15% w/w fresh royal jelly. Body size and mass measurements were recorded weekly for five weeks. We found the effects of royal jelly to be sex-dependent within crickets: females fed the royal jelly diet grew to be 30% heavier, and this effect was driven by significantly longer abdomens containing 67% more eggs compared to those fed the basal diet. There was a higher probability of crickets reaching adulthood after 35 days when fed royal jelly, and female mass was optimised at approximately 17% w/w royal jelly. Our results reveal that while a royal jelly dietary supplement can increase the yield of mass-reared insects, the life-history responses are species- and sex-specific.

ecology↗

bioRxiv2022

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 m), 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 m 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.

physiology↗