Immune responses in the haemolymph and antimicrobial peptide expression in the abdomen of Apis mellifera challenged with Spiroplasma melliferum CH-1

Integrated Information for Pathogenicity and Treatment of Spiroplasma

Spiroplasma, belonging to the class Mollicutes, is a small, helical, motile bacterium lacking a cell wall. Its host range includes insects, plants, and aquatic crustaceans. Recently, a few human cases of Spiroplasma infection have been reported. The diseases caused by Spiroplasma have brought about serious economic losses and hindered the healthy development of agriculture. The pathogenesis of Spiroplasma involves the ability to adhere, such as through the terminal structure of Spiroplasma, colonization, and invasive enzymes. However, the exact pathogenic mechanism of Spiroplasma remains a mystery. Therefore, we systematically summarize all the information about Spiroplasma in this review article. This provides a reference for future studies on virulence factors and treatment strategies of Spiroplasma.

The immune response of Locusta migratoria manilensis at different times of infection with Paranosema locustae

Paranosema locustae is an entomopathogenic microsporidia with promising potential for controlling agricultural pests, including Locusta migratoria manilensis. However, it has the disadvantage of having a slow insecticidal rate, and how P. locustae infection impacts the host immune response is currently unknown. The present study investigated the effect of P. locustae on the natural immune response of L. migratoria and the activities of enzymes that protect against oxidative stress. Infection with P. locustae increased the hemocytes and nodulation number of L. migratoria at the initial stage of infection. The hemocyte-mediated modulation of immune response was also affected by a decrease in the number of hemocytes 12 days postinfection. Superoxide dismutase activity in locusts increased in the early stages of infection but decreased in the later stages, whereas the activities of peroxidase (POD) and catalase (CAT) showed opposite trends may be due to their different mechanisms of action. Furthermore, the transcription levels of mRNA of antimicrobial peptide-related genes and phenoloxidase activity in hemolymph in L. migratoria were suppressed within 15 days of P. locustae infection. Overall, our data suggest that P. locustae create a conducive environment for its own proliferation in the host by disrupting the immune defense against it. These findings provide useful information for the potential application of P. locustae as a biocontrol agent.

Suppression of yolk formation, oviposition and egg quality of locust (Locusta migratoria manilensis) infected by Paranosema locustae

Locusta migratoria manilensis is one of the most important agricultural pests in China. The locust has high fecundity and consumes large quantities of food, causing severe damage to diverse crops such as corn, sorghum, and rice. Immunity against pathogens and reproductive success are two important components of individual fitness, and many insects have a trade-off between reproduction and immunity when resources are limited, which may be an important target for pest control. In this study, adult females L. migratoria manilensis were treated with different concentrations (5 × 106 spores/mL or 2 × 107 spores/mL) of the entomopathogenic fungus Paranosema locustae. Effects of input to immunity on reproduction were studied by measuring feeding amount, enzyme activity, vitellogenin (Vg) and vitellogenin receptor (VgR) production, ovary development, and oviposition amount. When infected by P. locustae, feeding rate and phenol oxidase and lysozyme activities increased, mRNA expression of Vg and VgR genes decreased, and yolk deposition was blocked. Weight of ovaries decreased, with significant decreases in egg, length and weight.Thus, locusts used nutritive input required for reproduction to resist invasion by microsporidia. This leads to a decrease in expression of Vg and VgR genes inhibited ovarian development, and greatly decreased total fecundity. P. locustae at 2 × 107 spores/mL had a more obvious inhibitory effect on the ovarian development in migratory locusts. This study provides a detailed trade-off between reproduction and immune input of the female, which provides a reliable basis to find pest targets for biological control from those trade-off processes.

Probiotic Potential and Effects on Gut Microbiota Composition and Immunity of Indigenous Gut Lactobacilli in Apis cerana

This study aimed to investigate the probiotic potential of gut indigenous lactic acid bacteria (LAB) originated from Apis cerana. Six Limosilactobacillus reuteri and one Lactobacillus helveticus were isolated from gut samples of A. cerana adult worker bee. All isolates antagonized the growth of pathogens including Salmonella typhimurium, Escherichia coli, Shigella flexneri, and Flavobacterium frigidimaris, and L. helveticus KM7 showed the greatest antimicrobial activity among them. All strains were sensitive to cefotaxime, amoxicillin, cephalothin, penicillin G, kanamycin, and vancomycin, moderately sensitive to novobiocin and resistant to gentamicin. Six out of seven strains were sensitive to ampicillin. L. helveticus KM7 was chosen to evaluate in vivo probiotic effect of adult worker bees of A. cerana through fed sucrose syrup supplemented with KM7. Administration of KM7 increased survival rate and gut LAB but decreased gut fungi and Enterococcus in honeybees. Expressions of genes related to antimicrobial peptides (AMPs) including Abaecin and Defensin were also induced in the gut of honeybees. The results suggested that L. helveticus KM7 with greater probiotic properties could improve the survival rate of adult worker honeybees of A. cerana through regulating gut microbiota and AMPs genes expression.

Honey Bee (Apis mellifera) Immunity

At the individual level, honey bees (Apis mellifera) rely on innate immunity, which operates through cellular and humoral mechanisms, to defend themselves against infectious agents and parasites. At the colony level, honey bees have developed collective defense mechanisms against pathogens and pests, such as hygienic and grooming behaviors. An understanding of the immune responses of honey bees is critical to implement strategies to reduce mortality and increase colony productivity. The major components and mechanisms of individual and social immunity of honey bees are discussed in this review.

Identification of reference markers for characterizing honey bee (Apis mellifera) hemocyte classes

Cell mediated immunity of the honey bee (Apis mellifera) involves the activity of several hemocyte populations, currently defined by morphological features and lectin binding characteristics. The objective of the present study was to identify molecular markers capable of characterizing subsets of honey bee hemocytes. We developed and employed monoclonal antibodies with restricted reactions to functionally distinct hemocyte subpopulations. Melanizing cells, known as oenocytoids, were defined by an antibody to prophenoloxidase, aggregating cells were identified by the expression of Hemolectin, and phagocytic cells were identified by a marker expressed on granulocytes. We anticipate that this combination of antibodies not only allows for the detection of functionally distinct hemocyte subtypes, but will help to further the exploration of hematopoietic compartments, as well as reveal details of the honey bee cellular immune defense against parasites and microbes.

Activation of Immune Genes in Leafhoppers by Phytoplasmas and Symbiotic Bacteria

Insect immunity is a crucial process in interactions between host and microorganisms and the presence of pathogenic, commensal, or beneficial bacteria may result in different immune responses. In Hemiptera vectors of phytoplasmas, infected insects are amenable to carrying high loads of phytopathogens, besides hosting other bacterial affiliates, which have evolved different strategies to be retained; adaptation to host response and immunomodulation are key aspects of insect-symbiont interactions. Most of the analyses published to date has investigated insect immune response to pathogens, whereas few studies have focused on the role of host immunity in microbiota homeostasis and vectorial capacity. Here the expression of immune genes in the leafhopper vector of phytoplasmas Euscelidius variegatus was investigated following exposure to Asaia symbiotic bacteria, previously demonstrated to affect phytoplasma acquisition by leafhoppers. The expression of four genes related to major components of immunity was measured, i.e., defensin, phenoloxidase, kazal type 1 serine protease inhibitor and Raf, a component of the Ras/Raf pathway. The response was separately tested in whole insects, midguts and cultured hemocytes. Healthy individuals were assessed along with specimens undergoing early- and late-stage phytoplasma infection. In addition, the adhesion grade of Asaia strains was examined to assess whether symbionts could establish a physical barrier against phytoplasma colonization. Our results revealed a specific activation of Raf in midguts after double infection by Asaia and flavescence dorée phytoplasma. Increased expression was observed already in early stages of phytoplasma colonization. Gut-specific localization and timing of Raf activation are consistent with the role played by Asaia in limiting phytoplasma acquisition by E. variegatus, supporting the involvement of this gene in the anti-pathogen activity. However, limited attachment capability was found for Asaia under in vitro experimental conditions, suggesting a minor contribution of physical phytoplasma exclusion from the vector gut wall. By providing evidence of immune modulation played by Asaia, these results contribute to elucidating the molecular mechanisms regulating interference with phytoplasma infection in E. variegatus. The involvement of Raf suggests that in the presence of reduced immunity (reported in Hemipterans), immune genes can be differently regulated and recruited to play additional functions, generally played by genes lost by hemipterans.