The costs of the immune memory within generations.

Immune response is evolutionary costly, but it is not clear whether these costs affect energetic expenditure (short-term cost), growth (medium-term cost), or reproduction (long-term cost). We tested the costs of immune memory in Tenebrio molitor against Metarhizium brunneum. To do this, we used two groups of T. molitor larvae: (a) the control group, which was injected first with Tween solution and 10 days later with M. brunneum and (b) the memory group, which was first injected with M. brunneum and 10 days later with M. brunneum. Compared to controls, larvae of the memory group were more likely to survive, but they also had an increased metabolic rate (CO2 production), spent a long time before becoming pupae, and had a shorter time from pupae to adulthood. In the adult stage, control females preferred control males, but there was no significant difference in the preference of memory females. Finally, control and memory males preferred control females. These results confirm that immune memory has costs in terms of energetic expenditure, growth, and reproduction. To the best of our knowledge, this is the first experimental demonstration that immune memory in larvae is traded-off with adult sexual selection involving mate choice.

An integrative study on biologically recovered polyhydroxyalkanoates (PHAs) and simultaneous assessment of gut microbiome in yellow mealworm.

Polyhydroxyalkanoates (PHAs) are produced in microbes as a source of carbon and energy storage. They are biodegradable and have properties similar to synthetic plastics, which make them an interesting alternative to petroleum-based plastics. In this study, a refined method of recovering PHA from Cupriavidus necator biomass was proposed by incorporating the use of the yellow mealworm (the larval phase of the mealworm beetle, Tenebrio molitor) as partial purification machinery, followed by washing of the fecal pellets with distilled water and sodium hydroxide. The PHA contents of the cells used in this study were 55wt% (produced from palm olein) and 60 wt% (produced from waste animal fats). The treatment of distilled water and NaOH further increased the purity of PHA to 94%. In parallel, analysis of the 16S rRNA metagenomic sequencing of the mealworm gut microbiome has revealed remarkable changes in the bacterial diversity, especially between the mealworms fed with cells produced from palm olein and waste animal fats. This biological recovery of PHA from cells is an attempt to move towards a green and sustainable process with the aim of reducing the use of harmful solvents and strong chemicals during polymer purification. The results obtained show that - purities of >90%, without a reduction in the molecular weight, can be obtained through this integrative biological recovery approach. In addition, this study has successfully shown that the cells, regardless of their origins, were readily consumed by the mealworms, and there is a correlation between the feed type and the mealworm gut microbiome.

Microbial community assessment of mealworm larvae (Tenebrio molitor) and grasshoppers (Locusta migratoria migratorioides) sold for human consumption.

In Western countries, the popularity of edible insects as an alternative animal protein source is increasing. Nevertheless, there is a lack of profound insight into the microbial safety and shelf life of living insects sold for human consumption. The purpose of this study was to characterise the microflora of fresh edible mealworm larvae and grasshoppers in a quantitative and qualitative way. Therefore, culture-dependent analyses (the total viable aerobic count, Enterobacteriaceae, lactic acid bacteria, yeasts and moulds, and bacterial endospores) and next-generation sequencing (454amplicon pyrosequencing) were performed. High microbial counts were obtained for both insect species. Different insect batches resulted in quite similar microbial numbers, except for bacterial endospores. However, the bacterial community composition differed between both insect species. The most abundant operational taxonomic unit in mealworm larvae was Propionibacterium. Also members of the genera Haemophilus, Staphylococcus and Clostridium were found. Grasshoppers were mainly dominated by Weissella, Lactococcus and Yersinia/Rahnella. Overall, a variety of potential spoilage bacteria and food pathogens were characterised. The results of this study suggest that a processing step with a microbiocidal effect is required to avoid or minimize risks involved with the consumption of edible insects.

Differential expression and costs between maternally and paternally derived immune priming for offspring in an insect.

1. When parasitized, both vertebrates and invertebrates can enhance the immune defence of their offspring, although this transfer of immunity is achieved by different mechanisms. In some insects, immune-challenged males can also initiate trans-generational immune priming (TGIP), but its expressions appear qualitatively different from the one induced by females similarly challenged. 2. The existence of male TGIP challenges the traditional view of the parental investment theory, which predicts that females should invest more into their progeny than males. However, sexual dimorphism in life-history strategies and the potential costs associated with TGIP may nevertheless lead to dissymmetric investment between males and females into the immune protection of the offspring. 3. Using the yellow mealworm beetle, Tenebrio molitor, we show that after parental exposure to a bacterial-like infection, maternal and paternal TGIP are associated with the enhancement of different immune effectors and different fitness costs in the offspring. While all the offspring produced by challenged mothers had enhanced immune defence, only those from early reproductive episodes were immune primed by challenged fathers. 4. Despite the fact that males and females may share a common interest in providing their offspring with an immune protection from the current pathogenic threat, they seem to have evolved different strategies concerning this investment.