The power of poop: Defecation behaviors and social hygiene in insects

A phytocytokine and its derived peptides in the frass of an insect elicit rice defenses

Upon recognizing elicitors derived from herbivores, many plants activate specific defenses. Most of the elicitors identified thus far are from the oral secretions and egg-laying fluids of herbivores; in contrast, herbivore fecal excreta have been sparsely studied in this context. In this study, we identified elicitors in the frass of the striped stem borer (SSB; Chilo suppressalis) larvae using a combination of molecular and chemical analyses, bioactivity tests and insect performance bioassays. Treating rice plants with SSB frass or a solution composed of SSB frass and buffer elicited mitogen-activated protein kinase (MPK) cascades and the jasmonic acid (JA)-signaling pathway. Moreover, the treatment induced both the expression of defense-related genes and the production of defensive compounds, and enhanced the resistance of rice plants to SSB. Heating SSB frass solution did not affect its induction activity, but eliminating proteins and peptides from the solution by adding proteinase K impaired its activity. Additional chemical analyses and bioassays revealed that the rice phytocytokine, immune response peptide 1(IRP1), together with some of its derived peptides in SSB frass, induced the MPK cascades, JA biosynthesis, the expression of defense genes and the production of defensive compounds in rice. These results reveal an important role for the plant-derived fecal peptide phytocytokine IRP1 and some of its derived peptides in inducing defenses in rice against SSB.

Ambrosia gall midges (Diptera: Cecidomyiidae) and their microbial symbionts as a neglected model of fungus-farming evolution

Ambrosia gall midges (AGMs) represent an intriguing group within the Cecidomyiidae, one of the most diversified dipteran families. AGMs form galls on plants, where they cultivate and consume fungal symbionts (phytomycetophagy). This mutualistic relationship may play a critical role in larval nutrition, gall morphogenesis, and protection against natural enemies. Although most other fungus-farming taxa have been intensively studied, AGMs have largely been neglected. This review synthesizes current knowledge on the diversity, biology, and ecological interactions of AGM, highlighting the intricate relationships with their fungal symbionts. The implications for adaptive radiation and speciation are critically considered, including how fungal associations may have facilitated ecological flexibility and diversification. We also tackle the processes of coevolution, not only between AGM and their fungal symbionts but also involving plants and parasitoids. We identify the most pressing issues and discrepancies in the current understanding the AGM-fungi interactions. Key areas of future research should include elucidating fungal acquisition and transmission mechanisms, determining the specificity and diversity of AGM-associated fungal communities, understanding the evolutionary pathways leading to phytomycetophagy, and addressing taxonomic challenges within the AGM group, where species identification has been complicated by reliance on gall morphology and host specificity.

How many do we need? Meeting the challenges of studying the microbiome of a cryptic insect in an orchard

The minimal sampling effort required to report the microbiome composition of insect surveyed in natural environment is often based on empirical or logistical constraints. This question was addressed with the white pine cone beetle, Conophthorus coniperda (Schwarz), a devastating insect pest of seed orchards. It attacks and stop the growth of the cones within which it will spend its life, on the ground. To survive, the bark beetle probably interacts with microorganisms involved in alimentation, cold adaptation, and dormancy stage. Deciphering the drivers and benefits of these microorganisms in an orchard first requires methodological development addressing variability of the white pine cone beetle microbiome. The number of insect guts integrated in composite samples prior to DNA extraction and the number of surveyed trees are two features expected to induce variability in recovered microbiome profiles. These two levels of heterogeneity were examined in an orchard experimental area where 12 white pine trees were sampled and 15 cones from each tree were grouped together. For each tree, 2, 3 and 4 insects were selected, their intestinal tract dissected, and the microbiome sequenced. The number of insects caused no significant incidence on the coverage of bacterial and fungal communities' composition and diversity (p > 0.8). There was more variability among the different trees. A sampling effort including up to 33 trees in an area of 1.1 ha is expected to capture 98% of the microbial diversity in the experimental area. Spatial variability has important implications for future investigations of cryptic insect microbiome.

Microplastic exposure reduced the defecation rate, altered digestive enzyme activities, and caused histological and ultracellular changes in the midgut tissues of the ground beetle (Blaps polychresta)

Concerns about microplastic (MP) pollution in terrestrial systems are increasing. It is believed that the overall amount of MPs in the terrestrial system could be 4-23 times higher than that in the ocean. Agricultural ecosystems are among the most polluted areas with MPs. Terrestrial organisms such as ground beetles, will be more vulnerable to MPs in various agricultural soil types because they are common in garden and agricultural areas. Therefore, this work aims to assess for the first time the potential adverse effects of chronic exposure for 30 days of ground beetles to a field-realistic concentration of 2 % (w/w) of three different irregularly shaped MPs polymers: Polystyrene (PS), polyethylene terephthalate (PET), and polyamide 6 (PA; i.e., nylon 6) on their health. The results showed no effect on beetle survival; nevertheless, there was a decrease in beetle defecation rate, particularly in beetles exposed to PS-MPs, and a change in the activity of midgut digestive enzymes. The effects on digestive enzymes (amylase, protease, lipase, and α-glucosidase) were polymer and enzyme specific. Furthermore, histological and cytological studies demonstrated the decomposition of the midgut peritrophic membrane, as well as abnormally shaped nuclei, vacuolation, disordered microvilli, necrosis of goblet and columnar cells, and necrosis of mitochondria in midgut cells. Given the importance of ground beetles as predators in most agricultural and garden settings, the reported adverse impacts of MPs on their health may impact their existence and ecological functions.

Fecal transplant allows transmission of the gut microbiota in honey bees

The study of the fecal microbiota is crucial for unraveling the pathways through which gut symbionts are acquired and transmitted. While stable gut microbial communities are essential for honey bee health, their modes of acquisition and transmission are yet to be confirmed. The gut of honey bees is colonized by symbiotic bacteria within 5 days after emergence from their wax cells as adults. Few studies have suggested that bees could be colonized in part via contact with fecal matter in the hive. However, the composition of the fecal microbiota is still unknown. It is particularly unclear whether all bacterial species can be found viable in the feces and can therefore be transmitted to newborn nestmates. Using 16S rRNA gene amplicon sequencing, we revealed that the composition of the honey bee fecal microbiota is strikingly similar to the microbiota of entire guts. We found that fecal transplantation resulted in gut microbial communities similar to those obtained from feeding gut homogenates. Our study shows that fecal sampling and transplantation are viable tools for the non-invasive analysis of bacterial community composition and host-microbe interactions. It also implies that contact of young bees with fecal matter in the hive is a plausible route for gut microbiota acquisition.

IMPORTANCE

Honey bees are crucial pollinators for many crops and wildflowers. They are also powerful models for studying microbiome-host interactions. However, current methods rely on gut tissue disruption to analyze microbiota composition and use gut homogenates to inoculate microbiota-deprived bees. Here, we provide two new and non-invasive approaches that will open doors to longitudinal studies: fecal sampling and transplantation. Furthermore, our findings provide insights into gut microbiota transmission in social insects by showing that ingestion of fecal matter can result in gut microbiota acquisition.

The Eurasian spruce bark beetle Ips typographus shapes the microbial communities of its offspring and the gallery environment

The Eurasian spruce bark beetle (Ips typographus) is currently the most economically relevant pest of Norway spruce (Picea abies). Ips typographus associates with filamentous fungi that may help it overcome the tree's chemical defenses. However, the involvement of other microbial partners in this pest's ecological success is unclear. To understand the dynamics of the bark beetle-associated microbiota, we characterized the bacterial and fungal communities of wild-collected and lab-reared beetles throughout their development by culture-dependent approaches, meta-barcoding, and quantitative PCR. Gammaproteobacteria dominated the bacterial communities, while the fungal communities were mainly composed of yeasts of the Saccharomycetales order. A stable core of microbes is shared by all life stages, and is distinct from those associated with the surrounding bark, indicating that Ips typographus influences the microbial communities of its environment and offspring. These findings coupled with our observations of maternal behavior, suggest that Ips typographus transfers part of its microbiota to eggs via deposition of an egg plug treated with maternal secretions, and by inducing an increase in abundance of a subset of taxa from the adjacent bark.

The tropical cookbook: Termite diet and phylogenetics—Over geographical origin—Drive the microbiome and functional genetic structure of nests

Termites are key decomposers of dead plant material involved in the organic matter recycling process in warm terrestrial ecosystems. Due to their prominent role as urban pests of timber, research efforts have been directed toward biocontrol strategies aimed to use pathogens in their nest. However, one of the most fascinating aspects of termites is their defense strategies that prevent the growth of detrimental microbiological strains in their nests. One of the controlling factors is the nest allied microbiome. Understanding how allied microbial strains protect termites from pathogen load could provide us with an enhanced repertoire for fighting antimicrobial-resistant strains or mining for genes for bioremediation purposes. However, a necessary first step is to characterize these microbial communities. To gain a deeper understanding of the termite nest microbiome, we used a multi-omics approach for dissecting the nest microbiome in a wide range of termite species. These cover several feeding habits and three geographical locations on two tropical sides of the Atlantic Ocean known to host hyper-diverse communities. Our experimental approach included untargeted volatile metabolomics, targeted evaluation of volatile naphthalene, a taxonomical profile for bacteria and fungi through amplicon sequencing, and further diving into the genetic repertoire through a metagenomic sequencing approach. Naphthalene was present in species belonging to the genera Nasutitermes and Cubitermes. We investigated the apparent differences in terms of bacterial community structure and discovered that feeding habits and phylogenetic relatedness had a greater influence than geographical location. The phylogenetic relatedness among nests' hosts influences primarily bacterial communities, while diet influences fungi. Finally, our metagenomic analysis revealed that the gene content provided both soil-feeding genera with similar functional profiles, while the wood-feeding genus showed a different one. Our results indicate that the nest functional profile is largely influenced by diet and phylogenetic relatedness, irrespective of geographical location.

Drosophila melanogaster microbiome is shaped by strict filtering and neutrality along a latitudinal cline

Microbiomes affect many aspects of host biology, but the eco-evolutionary forces that shape their diversity in natural populations remain poorly understood. Geographical gradients, such as latitudinal clines, generate predictable patterns in biodiversity at macroecological scales, but whether these macroscale processes apply to host-microbiome interactions is an open question. To address this question, we sampled the microbiomes of 13 natural populations of Drosophila melanogaster along a latitudinal cline in the eastern United States. The microbiomes were surprisingly consistent across the cline, as latitude did not predict either alpha or beta diversity. Only a narrow taxonomic range of bacteria were present in all microbiomes, indicating that strict taxonomic filtering by the host and neutral ecological dynamics are the primary factors shaping the fly microbiome. Our findings reveal the complexity of eco-evolutionary interactions shaping microbial variation in D. melanogaster and highlight the need for additional sampling of the microbiomes in natural populations along environmental gradients.

The fecal shield is a double-edged sword for larvae of a leaf beetle

Larvae of some leaf beetles carry masses of feces covering parts or all of the body, which is called a “fecal shield”. In general, the shield is thought to be a defense structure against natural enemies. However, some studies have suggested that defense effectiveness varies depending on the natural enemy. In the present study, we used a fecal retention leaf beetle Ophrida xanthospilota (Coleoptera: Chrysomelidae), and two local generalist predators (an ant, Camponotus japonicus (Hymenoptera: Formicidae) and a stinkbug, Arma custos (Hemiptera: Pentatomidae)) as a system to test the hypothesis that the fecal shield of O. xanthospilota plays different roles in predation behavior of different predators and can provide multiple chemical communication signals in predator-prey interactions. Prey bioassays showed that the fecal shield of O. xanthospilota larvae repelled the ant C. japonicus while attracting the stinkbug A. custos. The results also strongly demonstrated that hexane extracts of the fecal shield significantly repelled C. japonicus, while dichloromethane extracts did not inhibit ant predation. Interestingly, dichloromethane extracts attracted A. custos, but hexane extracts did not. Therefore, we suggest that the fecal shield is a double-edged sword for the larvae of O. xanthospilota. Our results also indicated that the risk-benefit tradeoff of an insect should be estimated at a community level involving multiple enemies (predators and parasites) and herbivores, rather than in a single prey-predator pair.