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Insects are important models for studying immunity in an ecological and evolutionary context. Yet, most empirical work on the insect immune system has come from phenotypic studies meaning we have a limited understanding of the genetic architecture of immune function in the sexes. We use nine highly inbred lines to thoroughly examine the genetic relationships between a suite of commonly used immune assays (haemocyte count, implant encapsulation, total phenoloxidase activity, antibacterial zone of inhibition and pathogen clearance) and resistance to infection by three generalist insect pathogens (the gram-negative bacterium Serratia marcescens, the gram-positive bacterium Bacillus cereus and the fungus Metarhizium robertsii) in male and female Gryllodes sigillatus. There were consistent positive genetic correlations between haemocyte count, antibacterial and phenoloxidase activity and resistance to S. marcescens in both sexes, but these relationships were less consistent for resistance to B. cereus and M. robertsii. In addition, the clearance of S. marcescens was genetically correlated with the resistance to all three pathogens in both sexes. Genetic correlations between resistances to the different pathogen species were inconsistent, indicating that resistance to one pathogen does not necessarily mean resistance to another. Finally, while there is ample genetic (co)variance in immune assays and pathogen resistance, these genetic estimates differed across the sexes and many of these measures were not genetically correlated across the sexes, suggesting that these measures could evolve independently in the sexes. Our finding that the genetic architecture of immune function is sex and pathogen specific suggests that the evolution of immune function in male and female G. sigillatus is likely to be complex. Similar quantitative genetic studies that measure a large number of assays and resistance to multiple pathogens in both sexes are needed to ascertain if this complexity extends to other species.

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BACKGROUND: Seasonal climate change may impose stress on mammal's immune system, but this has never been connected to wildlife endangerment reasons. This study focuses on Pseudois nayaur, a rare Chinese sheep facing a severe situation of disappearing. MATERIALS AND METHODS: Wild Pseudois nayaurs in Sichuan, China were observed in this research by an integrated method including habitat environment, foraging rules, and breeding activities investigation in ecology filed, accompanied with immunity research by peripheral blood, including erythrocyte, neutrophils, natural killer cells, and macrophages immunity by means of erythrocyte rosette, phagocytosis, lactate dehydrogenase release and acid alpha-naphthyl acetate esterase method, respectively. RESULTS: The results show that Pseudois nayaurs's innate and red blood cell immunity in autumn and winter Pseudois nayaurs and it may be the results of energy reallocation between reproduction and the immune system. In addition, the environment pressure found in Zhu Balong, Sichuan, China including food reduction, human disturbance, low temperature, and severe drought still existed, which may prevent the Pseudois nayaur from normal immunity enhancement before winter. CONCLUSIONS: In conclusion, the innate immunosuppression found in this study especially at their breeding season in autumn and winter may be the ignored cause of wild Pseudois nayaur's endangerment and should be considered in their protection strategy.

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The interplay among environment, demography, and host-parasite interactions is a challenging frontier. In the ocean, fundamental changes are occurring due to anthropogenic pressures, including increased disease outbreaks on coral reefs. These outbreaks include multiple parasites, calling into question how host immunity functions in this complex milieu. Our work investigates the interplay of factors influencing co-infection in the Caribbean sea fan octocoral, Gorgonia ventalina, using metrics of the innate immune response: cellular immunity and expression of candidate immune genes. We used existing copepod infections and live pathogen inoculation with the Aspergillus sydowii fungus, detecting increased expression of the immune recognition gene Tachylectin 5A (T5A) in response to both parasites. Cellular immunity increased by 8.16% in copepod infections compared to controls and single Aspergillus infections. We also detected activation of cellular immunity in reef populations, with a 13.6% increase during copepod infections. Cellular immunity was similar in the field and in the lab, increasing with copepod infections and not the fungus. Amoebocyte density and the expression of T5A and a matrix metalloproteinase (MMP) gene were also positively correlated across all treatments and colonies, irrespective of parasitic infection. We then assessed the scaling of immune metrics to population-level disease patterns and found random co-occurrence of copepods and fungus across 15 reefs in Puerto Rico. The results suggest immune activation by parasites may not alter parasite co-occurrence if factors other than immunity prevail in structuring parasite infection. We assessed non-immune factors in the field and found that sea fan colony size predicted infection by the copepod parasite. Moreover, the effect of infection on immunity was small relative to that of site differences and live coral cover, and similar to the effect of reproductive status. While additional immune data would shed light on the extent of this pattern, ecological factors may play a larger role than immunity in controlling parasite patterns in the wild. Parsing the effects of immunity and ecological factors in octocoral co-infection shows how disease depends on more than one host and one parasite and explores the application of co-infection research to a colonial marine organism.

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The tetranortriterpenoid azadirachtin (Aza) is a well-known insect growth disruptor of plant origin. Although its actions on insects have been extensively studied; fragmentary reports are available from the immunological point of view. Therefore, in the present study, total (THC) and differential hemocyte counts (DHC), nodulation, phenoloxidase (PO) activity, immune-reactive lysozymes and inducible nitric oxide (NO) were assessed, as measures of immune responses, in Sarcophaga argyrostoma 3rd instars challenged individually with M. luteus or Aza, or in combination with both compared to the control larvae. THC was significantly declined after 12 h and 24 h of treatment with Aza. DHC varied considerably; in particular, plasmatocytes were significantly decreased after 36 h and 48 h of treatment with Aza; whereas granulocytes were significantly increased. Nodulation was significantly increased with the increase of time after all treatments. Challenging with M. luteus significantly increased the activity of PO in hemocytes and plasma; whereas such activity was significantly decreased after treatment with Aza or combined Aza and M. luteus. Treatment with Aza or M. luteus alone or in couple significantly increased lysozyme activity of fat body, hemocytes and plasma. However, challenging with M. luteus significantly increased NO concentration in the same tissues. A hypothetical model of Aza as a potential mutagen is presented. However, no genotoxic effect was observed through tracking apoptosis-associated changes in Aza-treated hemocytes via flow cytometry-based apoptosis detection. Our study suggests that the integration of Aza, as an eco-friendly pesticide, with bacterial biopesticides may be a successful approach for controlling insect pests.

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Parasite spillover from invasive aliens to native species increases the risk of disease emergence within native biota-either by direct harm to the new host or by indirect effects like increased risks of secondary infection. One example for such a detrimental effect is the parasitic copepod Mytilicola intestinalis that infected blue mussels Mytilus edulis after being introduced into the North Sea in the early 20th century. Since 1949, the parasite was blamed for multiple mass mortalities of infested blue mussels but evidence for a direct causal involvement of M. intestinalis remained circumstantial. Here, we now examine the potential effects of primary infections by the invasive parasite on the susceptibility to secondary infections with virulent bacteria (Vibrio spp.) in a full factorial infection experiment combining parasite infection (control vs. infected) with different Vibrio infection treatments (control, bath challenge, injection) in environmental conditions that either favoured the host (ambient temperature) or the bacterium (elevated temperature). The influence of primary and secondary infections on cellular immunity (phagocytosis) and Vibrio load in the haemolymph was used to correlate these results to host survival. Our results suggest that the rate of secondary Vibrio infection is increased due to lower efficiency of the cellular immune response. As a consequence, the failure of clearing Vibrio from the haemolymph might increase mortality of mussels infected by M. intestinalis. This demonstrates that indirect effects of parasite invasions can outweigh direct effects of the infection highlighting the need for a more integrative approach to understand and predict the consequences of parasite invasions.

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The success of maternally transmitted endosymbiotic bacteria, such as Wolbachia, is directly linked to their host reproduction but in direct conflict with other parasites that kill the host before it reaches reproductive maturity. Therefore, symbionts that have evolved strategies to increase their host's ability to evade lethal parasites may have high penetrance, while detrimental symbionts would be selected against, leading to lower penetrance or extinction from the host population. In a natural population of the parasitoid wasp Hyposoter horticola in the Åland Islands (Finland), the Wolbachia strain wHho persists at an intermediate prevalence (∼50%). Additionally, there is a negative correlation between the prevalence of Wolbachia and a hyperparasitoid wasp, Mesochorus cf. stigmaticus, in the landscape. Using a manipulative field experiment, we addressed the persistence of Wolbachia at this intermediate level, and tested whether the observed negative correlation could be due to Wolbachia inducing either susceptibility or resistance to parasitism. We show that infection with Wolbachia does not influence the ability of the wasp to parasitize its butterfly host, Melitaea cinxia, but that hyperparasitism of the wasp increases in the presence of wHho. Consequently, the symbiont is detrimental, and in order to persist in the host population, must also have a positive effect on fitness that outweighs the costly burden of susceptibility to widespread parasitism.

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Hemocytes are crucial cells of the insect immune system because of their involvement in multiple immune responses including coagulation, phagocytosis and encapsulation. There are various types of hemocytes, each having a particular role in immunity, such that variation in their relative abundance affects the outcome of the immune response. This study aims to characterize these various types of hemocytes in larvae of the grapevine pest insect Eupoecilia ambiguella, and to assess variation in their concentration as a function of larval diet and immune challenge. Four types of hemocytes were found in the hemolymph of 5th instar larvae: granulocytes, oenocytoids, plasmatocytes and spherulocytes. We found that the total concentration of hemocytes and the concentration of each hemocyte type varied among diets and in response to the immune challenge. Irrespective of the diet, the concentration of granulocytes increased following a bacterial immune challenge, while the concentration of plasmatocytes and spherulocytes differentially varied between larval diets. The concentration of oenocytoids did not vary among diets before the immune challenge but varied between larval diets in response to the challenge. These results suggest that the resistance of insect larvae to different natural enemies critically depends on the effect of larval diet on the larvae's investment into the different types of hemocytes.

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Endosymbionts can fundamentally alter host physiology. Whether such changes are beneficial or detrimental to one or both partners may depend on the dynamics of the symbiotic relationship. Here we investigate the relationship between facultative symbionts and host immune responses. The pea aphid, Acyrthosiphon pisum, maintains an obligate primary symbiont, but may also harbour one or more facultative, secondary symbionts. Given their more transient nature and relatively recent adoption of a symbiotic lifestyle compared to primary symbionts, secondary symbionts may present a challenge for the host immune system. We assessed the response of several key components of the cellular immune system (phenoloxidase activity, encapsulation, immune cell counts) in the presence of alternative secondary symbionts, investigating the role of host and secondary symbiont genotype in specific responses. There was no effect of secondary symbiont presence on the phenoloxidase response, but we found variation in the encapsulation response and in immune cell counts based largely on the secondary symbiont. Host genotype was less influential in determining immunity outcomes. Our results highlight the importance of secondary symbionts in shaping host immunity. Understanding the complex physiological responses that can be propagated by host-symbiont associations has important consequences for host ecology, including symbiont and pathogen transmission dynamics.

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Many have argued that we may be able to extend life and improve human health through hormesis, the beneficial effects of low-level toxins and other stressors. But, studies of hormesis in model systems have not yet established whether stress-induced benefits are cost free, artifacts of inbreeding, or come with deleterious side effects. Here, we provide evidence that hormesis results in trade-offs with immunity. We find that a single topical dose of dead spores of the entomopathogenic fungus, Metarhizium robertsii, increases the longevity of the fruit fly, Drosophila melanogaster, without significant decreases in fecundity. We find that hormetic benefits of pathogen challenge are greater in lines that lack key components of antifungal immunity (Dif and Turandot M). And, in outbred fly lines, we find that topical pathogen challenge enhances both survival and fecundity, but reduces ability to fight off live infections. The results provide evidence that hormesis is manifested by stress-induced trade-offs with immunity, not cost-free benefits or artifacts of inbreeding. Our findings illuminate mechanisms underlying pathogen-induced life-history trade-offs, and indicate that reduced immune function may be an ironic side effect of the "elixirs of life."

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Advances in ecological immunity have illustrated that, like vertebrates, insects exhibit adaptive immunity, including induced changes in feeding behavior that aid the immune system. In particular, recent studies have pointed to the importance of protein intake in mounting an immune response. In this study, we tested the hypothesis that the polyphagous caterpillar Grammia incorrupta (H. Edwards) (Family: Erebidae) would adaptively change its feeding behavior in response to immune challenge, predicting that caterpillars would increase their intake of dietary protein. We further predicted that this response would enhance the melanization response, a component of the immune system that acts against parasitoids. We challenged the immune system using either tachinid fly parasitoids or a bead injection technique that has been used in studies to simulate parasitism, and measured feeding before and after immune challenge on diets varying in their macronutrient content. To evaluate the effects of diet on melanization, we quantified melanization of beads following feeding assays. Contrary to our prediction, we found that parasitized or injected caterpillars given a choice between high- and low-protein foods reduced their intake of the high-protein food. Furthermore, in a no-choice experiment, caterpillars offered food with a protein concentration that is optimal for growth reduced feeding following immune challenge, whereas those offered a low-protein food did not. Although variation in protein intake did not change the caterpillars' melanization response, increased carbohydrate intake did increase melanization, suggesting a prophylactic role for carbohydrates. We discuss alternative mechanisms by which variation in protein intake could negatively or positively affect parasitized caterpillars, including nutritional interactions with the caterpillar's self-medication response.

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Specialist and generalist insect herbivore species often differ in how they respond to host plant traits, particularly defensive traits, and these responses can include weakened or strengthened immune responses to pathogens and parasites. Accurate methods to measure immune response in the presence and absence of pathogens and parasites are necessary to determine whether susceptibility to these natural enemies is reduced or increased by host plant traits. Plant chemical traits are particularly important in that host plant metabolites may function as antioxidants beneficial to the immune response, or interfere with the immune response of both specialist and generalist herbivores. Specialist herbivores that are adapted to process and sometimes accumulate specific plant compounds may experience high metabolic demands that may decrease immune response, whereas the metabolic demands of generalist species differ due to more broad-substrate enzyme systems. However, the direct deleterious effects of plant compounds on generalist herbivores may weaken their immune responses. Further research in this area is important given that the ecological relevance of plant traits to herbivore immune responses is equally important in natural systems and agroecosystems, due to potential incompatibility of some host plant species and cultivars with biological control agents of herbivorous pests.