Protein feeding mediates sex pheromone biosynthesis in an insect

Neuroecology of alcohol risk and reward: Methanol boosts pheromones and courtship success in Drosophila melanogaster

Attraction of Drosophila melanogaster toward by-products of alcoholic fermentation, especially ethanol, has been extensively studied. Previous research has provided several interpretations of this attraction, including potential drug abuse, or a self-medicating coping strategy after mate rejection. We posit that the ecologically adaptive value of alcohol attraction has not been fully explored. Here, we assert a simple yet vital biological rationale for this alcohol preference. Flies display attraction to fruits rich in alcohol, specifically ethanol and methanol, where contact results in a rapid amplification of fatty acid-derived pheromones that enhance courtship success. We also identify olfactory sensory neurons that detect these alcohols, where we reveal roles in both attraction and aversion, and show that valence is balanced around alcohol concentration. Moreover, we demonstrate that methanol can be deadly, and adult flies must therefore accurately weigh the trade-off between benefits and costs for exposure within their naturally fermented and alcohol-rich environments.

Functional remodeling of gut microbiota and liver in laying hens as affected by fasting and refeeding after fasting

OBJECTIVE

Animals will experience energy deprivation processes such as moulting, clutching, migration and long-distance transportation under natural survival conditions and in production practices, and the body will trigger a series of adaptive metabolic changes during these processes. Fasting and refeeding after fasting can induce remodeling of nutrients and energy metabolism. This study aims to investigate the mechanisms by which the gut microbiota and liver of poultry respond to energy deprivation under specific conditions.

METHODS

Ninety 252-day-old laying hens were randomly divided into 3 groups: (1) fed ad libitum (control group); (2) fasted from day 13 to day 17 (fasting group); (3) fasted from day 1 to day 5, then refed on a specific feeding way (refeeding group). After that, the serum, liver, jejunum tissues, and cecum contents were sampled and sent for metabolome, transcriptome, morphology, and 16S rDNA sequencing analyses, respectively.

RESULTS

Results showed that food deprivation not only observably decreased the body weight, liver index, and the villus height and villus/crypt ratio of jejunum, but also significantly changed the gut microbiota compositions, serum metabolic profiles, and the hepatic gene expression patterns of laying hens, whereas these changes were effectively reversed by the following refeeding operation. At the same time, metabolome combined transcriptome analysis revealed that both serum differential metabolites and hepatic differential expressed genes (DEGs) were consistently enriched in the lipid and amino metabolism pathways, and strong correlations were synchronously found between the differential metabolites and both of the differential gut microbial genera and DEGs, suggesting the crosstalks among gut, liver and their resulting serum metabolic products.

CONCLUSION

The results suggested that the organism might coordinate to maintain metabolic homeostasis under energy deprivation through a combination of changes in gut microbial composition and hepatic gene expression.

A Stinkbug Salivary Protein Is Indispensable for Insect Feeding and Activates Plant Immunity

Salivary proteins secreted by phytophagous insects play pivotal roles in plant-insect interactions. A salivary protein RpSP27, from the stinkbug Riptortus pedestris, a devastating pest on soybean, was selected for studying due to its ability to induce cell death and activate immune responses in plants. RpSP27 localized to the endoplasmic reticulum and triggered reactive oxygen species burst. Virus-induced gene silencing assays showed RAR1 plays an essential role in RpSP27-induced cell death in Nicotiana benthamiana. Expression analyses revealed that RpSP27 is predominantly expressed in R. pedestris salivary glands. RNA interference-mediated silencing of RpSP27 in R. pedestris significantly reduced insect survival rates and altered feeding behavior by decreasing the formation of salivary sheaths on soybeans and reducing probing and feeding duration. Furthermore, the silencing of RpSP27 in R. pedestris mitigated the staygreen syndrome in soybeans, characterized by delayed senescence and pod abnormalities. This study elucidated the role of RpSP27 in the interaction between R. pedestris and soybean, presenting a potential target for pest management strategies to protect soybean crops from the detrimental effects of R. pedestris feeding.

Expression of a pheromone binding protein affected by timeless gene governs female mating behavior in Bactrocera dorsalis

BACKGROUND

The rhythmic mating behavior of insects has been extensively documented, yet the regulation of this behavior through sex pheromone sensing olfactory genes affected by the clock genes in the rhythm pathway remains unclear.

RESULTS

In this study, we investigated the impact of circadian rhythm on female recognition of male rectal Bacillus-produced sex pheromone in B. dorsolis. Behavioral and electrophysiological assays revealed a peak in both mating behavior and response to sex pheromones in the evening in females. Comparative transcriptome analysis of female heads demonstrated rhythmic expression of the Timeless gene-Tim and odorant binding protein gene-Pbp5, with the highest expression levels occurring in the evening. Protein structural modeling, tissue expression patterns, RNAi treatment, and physiological/behavioral studies supported Pbp5 as a sex pheromone binding protein whose expression is affected by Tim. Furthermore, manipulation of the female circadian rhythm resulted in increased morning mating activity, accompanied by consistent peak expression of Tim and Pbp5 during this time period. These findings provide evidence that insect mating behavior can be modulated by clock genes through their effects on sex pheromone sensing processes.

CONCLUSIONS

Our results also contribute to a better understanding of the molecular mechanisms underlying rhythmic insect mating behavior.

Clock genes regulate sex pheromone production and male mating ability in Bactrocera dorsalis

Many animals display physiological and behavioral activities limited to specific times of the day. Certain insects exhibit clear daily rhythms in their mating activities that are regulated by an internal biological clock. However, the specific genetic mechanisms underlying this regulation remain largely unexplored. Mating in the fruit fly Bactrocera dorsalis exhibits a daily rhythm and is dependent on sex pheromones produced in the male rectum. We used transcriptome sequencing and clustered regularly interspaced short palindromic repeats (CRISPR) / CRISPR-associated nuclease 9 techniques to understand whether the daily rhythmicity of mating in B. dorsalis and sex pheromone production in the rectum are regulated by clock genes. The results showed that the production of sex pheromones by B. dorsalis males is rhythmic (low during the day and high at night) and is influenced by clock genes. Knockout of the clock genes cryptochrome 1 (cry1) and timeless (tim) reduced the production of sex pheromones and significantly impaired mating ability in males. In addition, quantitative polymerase chain reaction results from 5 different tissues showed cry1 was highly expressed in the head, whereas tim was highly expressed in both the head and rectum (a key site for male sex pheromone production). Transcriptome analysis confirmed that cry1 (head) and tim (head and rectum) exhibit rhythmic expressions consistent with sex pheromone rhythmicity. These results suggest that cry1 may be related to a central clock neuron (like the suprachiasmatic nucleus), whereas the rhythmic expression of tim in the rectum indicates the potential presence of peripheral oscillators. Our study reveals new targets and ideas for improved control of the fruit fly.

How Insect Exocrine Glands Work

Exocrine glands release a secretion to the body surface or into a lumen and are likely to be found in all insect taxa. Their secretions are diverse, serving many physiological, behavioral, and defensive functions. Much research has characterized gland structure and secretion identity and function, but little research has attempted to understand how these glands work to release secretion amounts in a timescale appropriate to function: How are some (e.g., physiological) secretions released in small amounts over long times, while others (e.g., defense) are released in large amounts infrequently? We describe a qualitative model, comprising intracellular, extracellular, and external compartments for secretion storage; rates of movement of secretion from one compartment to the next; physicochemical properties of secretions; and controlling behaviors, which may explain the release dynamics of secretions from these glands. It provides a template for quantitative dynamic studies investigating the operation, control, release, and biomimetics of exocrine glands.

Molecular module for glucose production influences sex pheromone synthesis in Bactrocera dorsalis

Some insects have evolved beneficial relationships with intestinal microbes for sex pheromone production to communicate with conspecifics effectively. However, it is not clear whether the sex pheromone synthesis activity of intestinal microbes can be controlled by the host, and the molecular mechanisms need to be further unraveled. In this study, we find that rectal gland Bacillus species of male Bactrocera dorsalis specifically produce sex pheromones in the evening, which is significantly associated with glucose levels. In vitro Bacillus culture assays show that glucose levels significantly influence the amount of sex pheromone produced. Comparative rectal gland transcriptome analysis reveals that the expressions of the alpha-galactosidase gene (GLA), a Bactrocera dorsalis transcription factor (BDTF), and a pigment-dispersing factor (PDF) are responsible for producing glucose. Our findings reveal that the PDF-BDTF-GLA module influences the intestinal-microbe-produced sex pheromone by regulating glucose levels and advance our understanding of interactions between insects and their intestinal microbes.

The effects of diet and semiochemical exposure on male Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) metabolic rate at a range of temperatures

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is an invasive species that has rapidly spread across the African continent, endangering the security of agricultural industries. The sterile insect technique (SIT) is being investigated as a viable additional pest management tool to suppress B. dorsalis populations after its successful implementation in other parts of the world. There is evidence to suggest that pre-release nutritional and semiochemical treatments for sterilised males can enhance their competitive performance against wild type males in SIT programs. This study examined how sterilisation, a diet rich in protein (addition of yeast hydrolysate) or containing semiochemicals (methyl eugenol or eugenol) affected the resting metabolic (RMR) of male B. dorsalis at different temperatures (15 - 30 °C), measured using flow-through respirometry. Our results indicated that the negative effect of sterilisation on RMR decreased as temperature increased and that duration of exposure to semiochemicals for 1 to 4 days was not a significant influencing factor on male B. dorsalis RMR. Protein-rich diet increased average RMR, but the difference in RMR between dietary groups decreased as temperature increased. Semiochemical feeding reduced the average RMR in male B. dorsalis. The difference in RMR between males that consumed semiochemical and those that did not increased with as temperature increased.

The Sexual Dimorphism in Rectum and Protein Digestion Pathway Influence Sex Pheromone Synthesis in Male Bactrocera Dorsalis

Sexual dimorphism is a crucial aspect of mating and reproduction in many animals, yet the molecular mechanisms remain unclear. In Bactrocera dorsalis, sex pheromones trimethylpyrazine (TMP) and tetramethylpyrazine (TTMP) are specifically synthesized by Bacillus strains in the male rectum. In the female rectum, Bacillus strains are found, but TMP and TTMP are not, indicating sexually dimorphic differences in sex pheromone synthesis. Our anatomical observations and precursor measurements revealed significant differences in rectal structure and ammonium levels between sexes.  In vitro and in vivo experiments reveal that ammonium is vital for sex pheromone synthesis in rectal Bacillus strains. Comparative transcriptome analysis identified ammonium-producing genes (carboxypeptidase B and peptide transporter) in the protein digestion pathway that show much higher expression in the male rectum than in the female rectum. Knocking down the expression of either carboxypeptidase B (or inhibiting enzyme activity) or peptide transporter decreases rectal ammonium levels significantly, resulting in the failure of sex pheromone synthesis in the male rectum. This study provides insights into the presence of sexual dimorphism in internal organs and their functionalities in male-specific sex pheromone synthesis and has significant implications for understanding the molecular mechanisms underlying sex pheromone synthesis by symbionts in insects.

Reproductive behavior of fruit flies: courtship, mating, and oviposition

Many species of the Tephritidae family are invasive and cause huge damage to agriculture and horticulture, owing to their reproductive characteristics. In this review, we have summarized the existing studies on the reproductive behavior of Tephritidae, particularly those regarding the genes and external factors that are associated with courtship, mating, and oviposition. Furthermore, we outline the issues that still need to be addressed in fruit fly reproduction research. The review highlights the implications for understanding the reproductive behavior of fruit flies and discusses methods for their integrated management and biological control. © 2023 Society of Chemical Industry.

Differences in rectal amino acid levels determine bacteria-originated sex pheromone specificity in two closely related flies

Sex pheromones are widely used by insects as a reproductive isolating mechanism to attract conspecifics and repel heterospecifics. Although researchers have obtained extensive knowledge about sex pheromones, little is known about the differentiation mechanism of sex pheromones in closely related species. Using Bactrocera dorsalis and Bactrocera cucurbitae as the study model, we investigated how the male-borne sex pheromones are different. The results demonstrated that both 2,3,5-trimethylpyrazine (TMP) and 2,3,5,6-tetramethylpyrazine (TTMP) were sex pheromones produced by rectal Bacillus in the two flies. However, the TMP/TTMP ratios were reversed, indicating sex pheromone specificity in the two flies. Bacterial fermentation results showed that different threonine and glycine levels were responsible for the preference of rectal Bacillus to produce TMP or TTMP. Accordingly, threonine (glycine) levels and the expression of the threonine and glycine coding genes were significantly different between B. dorsalis and B. cucurbitae. In vivo assays confirmed that increased rectal glycine and threonine levels by amino acid feeding could significantly decrease the TMP/TTMP ratios and result in significantly decreased mating abilities in the studied flies. Meanwhile, decreased rectal glycine and threonine levels due to RNAi of the glycine and threonine coding genes was found to significantly increase the TMP/TTMP ratios and result in significantly decreased mating abilities. The study contributes to the new insight that insects and their symbionts can jointly regulate sex pheromone specificity in insects, and in turn, this helps us to better understand how the evolution of chemical communication affects speciation.

The effects of circularly polarized light on mating behavior and gene expression in Anomala corpulenta (Coleoptera: Scarabaeidae)

Light is an important abiotic factor affecting insect behavior. In nature, linearly polarized light is common, but circularly polarized light is rare. Left circularly polarized (LCP) light is selectively reflected by the exocuticle of most scarab beetles, including Anomala corpulenta. Despite our previous research showing that this visual signal probably mediates their mating behavior, the way in which it does so is not well elucidated. In this study, we investigated how LCP light affects not only mating behavior but also gene expression in this species using RNA-seq. The results indicated that disruption of LCP light reflection by females of A. corpulenta probably affects the process by which males of A. corpulenta search for mates. Furthermore, the RNA-seq results showed that genes of the environmental signaling pathways and also of several insect reproduction-related amino acid metabolic pathways were differentially expressed in groups exposed and not exposed to LCP light. This implies that A. corpulenta reproduction is probably regulated by LCP light-induced stress. Herein, the results show that LCP light is probably perceived by males of the species, further mediating their mating behavior. However, this hypothesis needs future verification with additional samples.