Early physiological response of potato plants to entomopathogenic fungi under hydroponic conditions

Endophytic entomopathogenic fungi are promising agents for the promotion of plant growth, the activation of immunity, and protection against phytopathogens. However, physiological changes in plants after treatment with fungi are insufficiently studied. We investigated the effect of potato inoculation with conidia from Metarhizium robertsii and Beauveria bassiana on the growth (fresh and dry weight, length of shoots and roots, counts of stolons and leaves, and total surface area of leaves) and physiological parameters (pigment contents, free proline and malondialdehyde content, and activity of antioxidant enzymes) at the initial stage of the plant–fungus interaction (seven days) under hydroponic conditions. The results showed that the fungi could act as an immune-modulating factor for plants based on the increase in malondialdehyde and proline contents. At the same time, we observed growth retardation and a decrease in the content of photosynthetic pigments, which may be caused by a tradeoff between plant growth and the immune response

Improvement of bait method for isolation of entomopathogenic fungi from soil

An increase of the sensitivity of the bait method of entomopathogenic fungi isolation from the soil was registered under the use of larvae Galleria mellonella envenomated by ectoparasitoid Habrobracon hebetor. Further, modified method will allow to isolate fungi from soil with low titer of colony forming unit, particularly from steppes soils.Работа выполнена при финансовой поддержке РФФИ (проект 15–04–02322_а) и Президента РФ (МК–6278.2015.4.)

Fungus Metarhizium robertsii and neurotoxic insecticide affect gut immunity and microbiota in Colorado potato beetles

Fungal infections and toxicoses caused by insecticides may alter microbial communities and immune responses in the insect gut. We investigated the effects of Metarhizium robertsii fungus and avermectins on the midgut physiology of Colorado potato beetle larvae. We analyzed changes in the bacterial community, immunity- and stress-related gene expression, reactive oxygen species (ROS) production, and detoxification enzyme activity in response to topical infection with the M. robertsii fungus, oral administration of avermectins, and a combination of the two treatments. Avermectin treatment led to a reduction in microbiota diversity and an enhancement in the abundance of enterobacteria, and these changes were followed by the downregulation of Stat and Hsp90, upregulation of transcription factors for the Toll and IMD pathways and activation of detoxification enzymes. Fungal infection also led to a decrease in microbiota diversity, although the changes in community structure were not significant, except for the enhancement of Serratia. Fungal infection decreased the production of ROS but did not affect the gene expression of the immune pathways. In the combined treatment, fungal infection inhibited the activation of detoxification enzymes and prevented the downregulation of the JAK-STAT pathway caused by avermectins. The results of this study suggest that fungal infection modulates physiological responses to avermectins and that fungal infection may increase avermectin toxicosis by blocking detoxification enzymes in the gut

Horizontal transmission of entomopatho genic fungi by ectoparasitoid Habrobra conhebetor

Experiments were carried out on the laboratory system Galleria mellonella (Lepidoptera, Piraliidae) — Habrobracon hebetor (Hymenopera, Braconidae) — Beauveria bassiana (Hypocreales, Cordycipitaceae). We found that contamination of H. hebetor ovipositor with low titers of conidia B. bassiana and following envenomation of G. mellonella larvae led to mycoses followed by host colonization and conidia formation. In addition H. hebetor females transmitted fungal conidia from infected (6 hours post inoculation with conidia) to native G. mellonella larvae, and this transmission led to successful mycosis of native host larvae. The decreasing of cellular and humoral immune reactions, significant increasing of adhesion and germination of fungus on cuticle of envenomated larvae were registered. As result susceptibility of envenomated G. mellonella larvae to fungal infection was increased in thousands times compared with native control. Thus the paralyzation and strong inhibition of immune reactions of larvae by venom of H. hebetor allow minimize quantity of transmitting with parasitoid fungal inoculum. We assumed that «paralyzing» parasitoids can take part in transmission of entomopathogenic fungi particularly in out-of-the-way places (shelters) as well as disperse of fungal infection under low density of hosts.Работа выполнена при финансовой поддержке РФФИ (проект 15–04–02322_а) и Президента РФ (МК–6278.2015.4.)

Can Insects Develop Resistance to Insect Pathogenic Fungi?

This paper presents new, important information on the microevolution of insect resistance to the insect pathogenic fungus Beauveria bassiana which will have far-reaching implications for the development of insect pathogenic fungi as biological control agents. We placed successive generations of a melanic population of the Greater wax moth, Galleria mellonella, under constant selective pressure from the insect pathogenic fungus, Beauveria bassiana. Enhanced fungal resistance was observed and larvae from the 25th generation were studied in detail to uncover mechanisms underpinning resistance, and the possible cost of those survival strategies. There are 3 novel, core findings from the study:1.Antifungal resistance in these insects is pathogen species-specific, and probably arises through trans-generational immune priming. The resistance was less obvious in earlier generations, suggesting subtle cumulative changes that are only fully apparent in the 25th generation. 2.The insect’s fecundity is already pushed close to minimum by its melanic phenotype. Therefore, the additional drain on resources required to boost antifungal defence still more, comes not from further compromising life history traits but via a re-allocation of the insect’s immune defences. Specifically during B. bassiana infection, systemic (fat body and hemocoel) responses, particularly the expression of antimicrobial peptides, are damped down in favour of a tailored repertoire of enhanced responses in the integument (cuticle and epidermis) – the foremost and most important barrier to natural fungal infection. 3.A previously-overlooked range of putative stress-management factors are activated during the specific response of selected insects to B. bassiana. This too occurs primarily in the integument, and contributes to antifungal defense and/or helps ameliorate the damage inflicted by the fungus or the host’s own immune responses during the battle between host and pathogen.No other study to date has examined so many genes in this context. Indeed, we show that the epidermis has a great capacity to express defense and stress-management genes as well as the fat body (which is the main tissue producing antimicrobial peptides and has been the traditional focus of attention). We therefore propose a “be specific / fight locally / de-stress” model to explain resource allocation and defence priorities for insects selected for superior resistance to insect-pathogenic fungi. However, we also show that these insects are less fecund and probably at no evolutionary advantage in the wild, implying that the risk is small of biological control agents failing in the field

Changes of the Antioxidant Status and System of Generation of Free Radicals in Hemolymph of Galleria mellonella Larvae at Microsporidiosis

Abstract-Changes of superoxide dismutase (SOD) and glutathione S transferase (GST) activities as well as of the content of SH containing compounds were revealed in hemolymph of the native and the Vairimorpha ephestiae microsporidian infected greater wax moth Galleria mellonella larvae. The SOD and GST activities in hemolymph of infected insects decreased at the stage of merogony, whereas during massive sporulation the enzymatic antioxidant activity in host tissues was higher than in control. By the ESR spectroscopy method, using the 1 hydroxy 3 carboxy pyrrolidinespin trap, generation of free radicals in hemolymph of infected insects was shown to decrease only at the stage of sporogony. The phenoloxidase activity in lymph was lower at acute microsporidiosis than in native larvae. The hemolymph concentration of thiol containing proteins in infected insects did not differ from that in control. We suggest that decrease of generation of free radicals in hemolymph of the greater wax moth larvae at the stage of sporogony is due to a suppression of the prophenoloxidase system and an elevation of the antioxidant activity

Original Russian Text ©

It is known that crop plants' induced resistance to phyllophages, which is due to accumulation of secondary metabolites, decreases the viability of phyllophages and changes the sensitivity to entomopathogens It is known that tannins, including tannic acid, can form complexes with proteins; when oxidized to quinones in the midgut of insect, they can produce semiquinone radicals and other forms of reactive oxygen species In view of this, the goal of this study was to investigate the effect of a phenolic compound, tannic acid, on the development of L. dispar and its sensitivity to nuclear polyhedrosis. The ratio between the concentrations of oxidized and reduced thiol-containing compounds in insect midguts-an index reflecting the antioxidant status of the insect-was used as a criterion of the effect of this allelochemical on insect's organism. MATERIALS AND METHODS This study was performed with the gypsy moth ( L. dispar L., Lepidoptera: Lymantridae) caterpillars. The insects were collected at the egg phase in the natural population and then grown under laboratory conditions. The experiments were performed in spring and summer. The insects were grown either in an artificial nutrient medium in Petri dishes or on birch shoots in rearing cages at 23-25 ° C under at 16-h light period per day. Forage was treated with 0.9% aqueous solution of tannic acid (Sigma, United States). This concentration corresponds to the content of tannins in birch leaves defoliated in the previous year Biochemical analysis of the midgut was performed using the fourth-instar caterpillars on the fourth da

The effect of population density of Lymantria dispar (Lepidoptera: Erebidae) on its fitness, physiology and activation of the covert nucleopolyhedrovirus

After high population densities of insect defoliators there is often a dramatic decrease in their abundance due to various limiting factors. Here, we compared gypsy moth larvae (Lymantria dispar L.) reared singly and in crowded conditions. We compared a number of physiological parameters of these insects and the effect of L. dispar population density on the activation of covert baculovirus infections in the larvae. It was found that the population density of gypsy moth larvae did not affect the mortality due to the activation of the covert virus infection or the total mortality. On the other hand, solitary-reared larvae were heavier, took longer to develop, and showed a four-fold higher concentration of dopamine in their haemolymph than larvae reared in groups. Thus, we demonstrated that an increase in the population density of larvae per se facilitates some changes in fi tness and innate immunity traits but is not related to the activation of covert baculovirus infection. We suggest that an increase in population density does not increase the risk of epizootics triggered by the activation of covert baculovirus infection and that researchers should pay more attention to studying density-associated factors, such as starvation

A Diet with Amikacin Changes the Bacteriobiome and the Physiological State of <i>Galleria mellonella</i> and Causes Its Resistance to <i>Bacillus thuringiensis</i>

Environmental pollution with antibiotics can cause antibiotic resistance in microorganisms, including the intestinal microbiota of various insects. The effects of low-dose aminoglycoside antibiotic (amikacin) on the resident gut microbiota of Galleria mellonella, its digestion, its physiological parameters, and the resistance of this species to bacteria Bacillus thuringiensis were investigated. Here, 16S rDNA analysis revealed that the number of non-dominant Enterococcus mundtii bacteria in the eighteenth generation of the wax moth treated with amikacin was increased 73 fold compared to E. faecalis, the dominant bacteria in the native line of the wax moth. These changes were accompanied by increased activity of acidic protease and glutathione-S-transferase in the midgut tissues of larvae. Ultra-thin section electron microscopy detected no changes in the structure of the midgut tissues. In addition, reduced pupa weight and resistance of larvae to B. thuringiensis were observed in the eighteenth generation of the wax moth reared on a diet with amikacin. We suggest that long-term cultivation of wax moth larvae on an artificial diet with an antibiotic leads to its adaptation due to changes in both the gut microbiota community and the physiological state of the insect organism