Bacterial decomposition of insects post-Metarhizium infection: Possible influence on plant growth

Strains of entomopathogenic fungi may have substantial differences in their final stages of mycosis. Insect cadavers are usually overgrown with mycelium after colonization of the insect body, but in many cases, bacterial decomposition of the colonized hosts occurs. We used two Metarhizium robertsii strains in the work: Mak-1 (cadavers become overgrown with mycelium and conidia) and P-72 (cadavers decay after fungal colonization). We conducted a comparative analysis of gut and cadaver microbiota in Colorado potato beetle larvae using 16S rRNA gene sequencing after infection with these strains. In addition, we estimated the content of different forms of nitrogen in cadavers and the influence of cadavers on the growth of Solanum lycopersicum on sand substrates under laboratory conditions. It was shown that infections did not lead to a significant shift in the midgut bacterial communities of infected insects compared to those of untreated insects. Importantly, bacterial communities were similar in both types of cadaver, with predominantly enterobacteria. Decomposing cadavers (P-72) were characterized by increased nitrate and ammonium, and they had a stronger growth-promoting effect on plants compared to cadavers overgrown with mycelium and conidia (Mak-1). We also estimated the colonization and growth of plants after treatment with conidia of both strains cultivated on artificial medium. Both cultures successfully colonized plants, but strain P-72 showed stronger growth promotion than Mak-1. We propose that the use of deviant strains that are unable to sporulate on cadavers leads to a faster (though only passive) flow of nitrogen from killed insects to plants.     

Fungal infection dynamics in response to temperature in the lepidopteran insect Galleria mellonella

This study examines how the dynamics of fungus–insect interactions can be modulated by temperature. The wax moth, Galleria mellonella, is a well‐studied and important model insect whose larvae in the wild develop optimally at around 34 °C in beehives. However, surprisingly little research on wax moths has been conducted at relevant temperatures. In this study, the entomopathogenic fungus Metarhizium robertsii inflicted rapid and substantial mortality on wax moth larvae maintained at a constant temperature of 24 °C, but at 34 °C a 10 fold higher dose was required to achieve an equivalent mortality. The cooler temperature favored fungal pathogenicity, with condial adhesion to the cuticle, germination and hemocoel invasion all significantly enhanced at 24 °C, compared with 34 °C. The wax moth larvae immune responses altered with the temperature, and with the infective dose of the fungus. Enzyme‐based immune defenses (lysozyme and phenoloxidase) exhibited enhanced activity at the warmer temperature. A dramatic upregulation in the basal expression of galiomicin and gallerimycin was triggered by cooling, and this was augmented in the presence of the fungus. Profiling of the predominant insect epicuticular fatty acids revealed a 4–7 fold increase in palmetic, oleic and linoleic acids in larvae maintained at 24 °C compared with those at 34 °C, but these failed to exert fungistatic effects on topically applied fungus. This study demonstrates the importance of choosing environmental conditions relevant to the habitat of the insect host when determining the dynamics and outcome of insect/fungus interactions, and has particular significance for the application of entomopathogens as biocontrol agents.     

Salinity adaptations in the gastropodsLittorina mandshurica andLittorina squalida at different stages of ontogenesis

Salinity adaptations of the gastropodsLittorina mandshurica andL. squalida were studied at different stages of their life cycles.L. mandshurica exhibited a higher degree of adaptation to variations in salinity thanL. squalida at all developmental stages. Egg masses did not protect embryos from desalination; the larvae inside the egg masses were capable of adapting to diluted seawater. As larvae developed in egg masses, their adaptive capabilities increased. At the time of hatching, the salinity tolerance of larvae differed little, if at all, from that of adults. It is assumed that pelagic egg capsules provide an advantage in the distribution of a species.     

Studies of the possibility that RNA polymerase participates in mutagenesis in bacteriophage T4

An increased rate of mutagenesis of phage T₄ by base analogues was observed in Escherichia coli strains resistant to both rifampicin and streptolydigin and shown to have defective RNA polymerase. The results suggest that RNA polymerase may be involved in the production of mutations by errors of replication.     

Synergistic action of entomopathogenic hyphomycetes and the bacteria <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> ssp. <Emphasis Type="Italic">morrisoni</Emphasis> in the infection of Colorado potato beetle <Emphasis Type="Italic">Leptinotarsa decemlineata</Emphasis>

A synchronous coinfection of the Colorado potato beetle Leptinotarsa decemlineata (Say) with the entomopathogenic bacteria Bacillus thuringiensis ssp. morrisoni Bonnifoi & de Barjak var. tenebrionis Krieg et al. and hyphomycete Metarhizium anisopliae (Metsch.) Sorokin or Beauveria bassiana (Bals.) Vuill leads to the rapid death of 95–100% of larvae. The bacteria arrest the nutrition of insects, while the fungal spores kill the weakened larvae. The synergistic effect of two pathogens is recorded at a relatively low hyphomycete titer (1–5 × 10⁶ conidia/ml) and is evident in the mortality dynamics at all larval ages. These bacterial and fungal pathogens display no antagonism on artificial nutrient media. This microbial complex is highly efficient under natural conditions (80–90% larval mortality rate and no plant defoliation).     

The activity of nonspecific esterases and glutathione-S-transferase in <Emphasis Type="Italic">Locusta migratoria</Emphasis> larvae infected with the fungus <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> (Ascomycota,Hypocreales)

The activity of nonspecific esterases and glutathione-S-transferase in whole body homogenates, hemolymph plasma, and fat body of the larvae of the locust Locusta migratoria was analyzed during development of infection with the fungus Metarhizium anisopliae. The lethal dose of the fungus (LC₈₀) was found to enhance the activity of detoxifying enzymes in the whole body homogenate of the larvae on the 3rd day after infection. The activity of nonspecific esterases and glutathione-S-transferase in the plasma and fat body of the infected larvae increased on the 3rd day but dropped to the control levels by the 6th day, during the acute period of infection. The detoxifying enzymes may participate in defense reactions at the early stage of the acute fungal infection.     

Immunosuppression of insects by the venom of <Emphasis Type="Italic">Habrobracon hebetor</Emphasis> increases the sensitivity of bait method for the isolation of entomopathogenic fungi from soils

We evaluated the susceptibility of Galleria mellonella larvae immunosuppressed by the venom of Habrobracon hebetor to soil entomopathogenic ascomycetes with the use of bait method. It was found that the sensitivity of the modified method was significantly (by almost 200 times) increased as compared with the standard procedure, which provided the isolation of fungi when their abundance was extremely low. Envenomated larvae were more susceptible to the entomopathogenic but not saprotrophic fungi. We presented results of isolation of the entomopathogenic fungi from soils in different climatic zones (from the forest tundra to the steppe) using an improved procedure.     

The Reaction of Mytilus trossulus Larvae (Bivalvia,Mytilidae) to Desalination and Increase of Water Column Temperature

Under homogeneous salinity and temperature conditions and uniform daylight, the early larvae of the Pacific mussel Mytilus trossulus (blastulae and trochophores) accumulated in the uppermost layer of water column, while the late larvae tend to concentrate at the bottom. In a water column with a temperature or salinity gradient, the early larvae accumulated at the surface even when the salinity and temperature conditions were incompatible with their life activity. The distribution of the late larvae was different as they were able to leave water of unfavorable temperature and salinity and accumulate at the bottom.     

Phenotypic variability of environmental isolates of the entomopathogenic fungus <Emphasis Type="Italic">Beauveria bassiana</Emphasis>

A total of 35 isolates of Beauveria bassiana (Bals.) Vuill. isolates obtained from various insects of Novosibirsk oblast were investigated. The fungal morphotypes were found to include cultures of high, medium, and low virulence. Low correlation (r < 0.48) was observed between virulence and the morphophysiological characteristics of the isolates (lipase and protease activity, biomass, radial growth rate, conidia productivity, and relief). Isolates exhibiting high virulence to insects of a certain order proved to be virulent to the insects of other orders. A high correlation (r > 0. 74) was revealed between the virulence of the isolates to the potato beetle Leptinotarsa decemlineata Say and the locusts Calliptamus barbarus Costa and Locusta migratoria L. Isolates obtained from insects of the same species in the same site may differ significantly in virulence.