Characterization of the synergistic interaction between Beauveria bassiana strain GHA and Bacillus thuringiensis morrisoni strain tenebrionis applied against Colorado potato beetle larvae

Exposure of honey bees to mixtures of microbial biopesticides and their effects on bee survival under laboratory conditions

Biopesticides, having as active ingredients viruses, bacteria, or fungi, are developed to substitute or reduce the use of chemical plant protection products in different agrosystems. Though the application of mixtures containing several products is a common practice, interactions between microbial biopesticides and related effects on bees as non-target organisms have not been studied yet. In the current study, we exposed winter bees to five different microbial-based products and their combinations at the maximum recommended application rate to assess their responses. Laboratory oral exposure tests (acute/chronic) to single or binary products were conducted. Survival and food consumption of the tested bees were evaluated over the experimental duration. Our results show that some product combinations have potential additive or synergistic effects on bees, whereas others did not affect the bee's survival compared to the control. Exposure of tested bees to the most critical combination of products containing Bacillus thuringiensis aizawai ABTS-1857 and B. amyloliquefaciens QST 713 strongly resulted in a median lifespan of 4.5 days compared to 8.0 and 8.5 days after exposure to the solo products, respectively. The exposure to inactivated microorganisms by autoclaving them did not differ from their respective uncontaminated negative controls, indicating effects on bee mortality might originate in the treatment with the different microorganisms or their metabolites. Further investigations should be conducted under field conditions to prove the magnitude of observed effects on bee colonies and other bee species.

Biological Control of Diamondback Moth-Increased Efficacy with Mixtures of Beauveria Fungi

Diamondback moth (DBM) is an important horticultural pest worldwide as the larvae of these moths feed on the leaves of cruciferous vegetables. As DBM has developed resistance to more than 100 classes of synthetic insecticides, new biological control options are urgently required. Beauveria species are entomopathogenic fungi recognized as the most important fungal genus for controlling a wide range of agricultural, forestry, and veterinary arthropod pests. Previous research, aimed at developing new Beauveria-based biopesticides for DBM, has focused on screening single isolates of Beauveria bassiana. However, these fungal isolates have individual requirements, which may limit their effectiveness in some environments. This current study separately assessed 14 Beauveria isolates, from a range of habitats and aligned to four different species (Beauveria bassiana, B. caledonica, B. malawiensis, and B. pseudobassiana), to determine the most effective isolate for the control of DBM. Further assays then assessed whether selected combinations of these fungal isolates could increase the overall efficacy against DBM. Six Beauveria isolates (three B. bassiana and three B. pseudobassiana) achieved high DBM mortality at a low application rate with the first documented report of B. pseudobassiana able to kill 100% of DBM larvae. Further research determined that applications of low-virulent Beauveria isolates improved the control of DBM compared to mixtures containing high-virulent isolates. This novel approach increased the DBM pest mortality and shortened the time to kill.

Interactions Between Two Invertebrate Pathogens: An Endophytic Fungus and an Externally Applied Bacterium

The members of family Noctuidae exist in diverse environments and many species from this group are of agriculture importance, particularly Helicoverpa spp. Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a major pest of many legumes and cereal crops. Due to environmental and regulatory concerns, safe alternatives to broad spectrum chemical insecticides are needed for the control of key noctuid pests such as H. armigera. A strain of Beauveria bassiana (Cordycipitaceae: Hypocreales) was evaluated for its ability to colonize endophytically in chickpea plants, and its effectiveness against second (L2) and fourth (L4) larval instars of H. armigera. B. bassiana was inoculated to chickpea plants through injection and endophytic establishment was confirmed by re-isolating the fungi from leaf samples. A detached leaf assay was used to evaluate pathogenicity. Bacillus thuringiensis was also applied to both larval stages through leaf dip method. In a novel approach, combined treatments of bacteria and endophytic fungi were compared with single-pathogen treatments. Relative to the single treatments, the combined pathogen treatments exhibited an increase in larval mortality, and decrease in pupation, adult emergence and egg eclosion. Specifically, synergistic effects on mortality were observed when larvae were exposed to simultaneous application of B. bassiana (1 × 108 conidia ml-1) with B. thuringiensis (0.75 μg ml-1). Both instars exhibited varying level of growth, development, frass production, diet consumption and fecundity when exposed to the chickpea leaves inoculated with endophytic B. bassiana and dipped with sub-lethal doses of B. thuringiensis. These findings indicate that the integrated application of endophytic colonized B. bassiana and B. thuringiensis can be effectively used against H. armigera.

Integration of Entomopathogenic Fungi into IPM Programs: Studies Involving Weevils (Coleoptera: Curculionoidea) Affecting Horticultural Crops

Weevils are significant pests of horticultural crops and are largely managed with insecticides. In response to concerns about negative impacts of synthetic insecticides on humans and the environment, entomopathogenic fungi (EPF) have been developed as an alternative method of control, and as such appear to be "ready-made" components of integrated pest management (IPM) programs. As the success of pest control requires a thorough knowledge of the biology of the pests, this review summarises our current knowledge of weevil biology on nut trees, fruit crops, plant storage roots, and palm trees. In addition, three groups of life cycles are defined based on weevil developmental habitats, and together with information from studies of EPF activity on these groups, we discuss the tactics for integrating EPF into IPM programs. Finally, we highlight the gaps in the research required to optimise the performance of EPF and provide recommendations for the improvement of EPF efficacy for the management of key weevils of horticultural crops.

Endophytic Strain Bacillus subtilis 26DCryChS Producing Cry1Ia Toxin from Bacillus thuringiensis Promotes Multifaceted Potato Defense against Phytophthora infestans (Mont.) de Bary and Pest Leptinotarsa decemlineata Say

Novel properties of a previously obtained Bacillus subtilis 26DCryChS strain are described. The B. subtilis 26DCryChS strain is able to produce Cry1Ia δ-endotoxin from B. thuringiensis B-5351 and to exist in internal plant tissues of potato plants in the same manner as the endophytic B. subtilis 26D source strain (487 ± 53 and 420 ± 63 CFU*10³/g, respectively). B. subtilis 26DCryChS, as much as the original B. subtilis 26D strain, inhibited mycelium growth of oomycete Phytophthora infestans (Mont.) de Bary and reduced late blight symptoms development on plants by 35% compared with non-treated ones, as well as showed insecticidal activity against Leptinotarsa decemlineata. Production of the fluorescent GFP protein in the B. subtilis 26D genome allowed visualizing the endophytes around damaged sites on beetle intestines. Bacillus strains under investigation induced systemic resistance to P. infestans and L. decemlineata through the activation of the transcription of PR genes in potato plants. Thus, the B. subtilis 26DCryChS strain was able to induce transcription of jasmonate-dependent genes and acquired the ability to promote transcription of a salicylate-dependent gene (PR1) in plants infected with the late blight agent and damaged by Colorado potato beetle larvae. The B. subtilis 26DCryChS strain could be put forward as a modern approach for biocontrol agents design.

Pathogenic post-effect of entomopathogenic fungi on phytophagous pests and entomophagous biocontrol agents

Phytosanitary optimization of agricultural ecosystems under conditions of glasshouses and organic farming urgently demands guaranteed effect of plant protection. This can be achieved only through effective exploitation of a complex of biological agents, including arthropod predators and parasites, entomopathogenic fungi, nematodes and other microbes. Entomopathogenic fungi Beauveria bassiana and Lecanicillium muscarium are characterized by facultative parasitism and possess high potential to control phytophagous insects, including pests of vegetable crops in glasshouses. In aphids, fungal pathogenesis was found to be comprised of primary mycosis and toxigenic post-effect in a row of consequent generations. For example, L. muscarium and B. bassiana had an adverse effect on fertility and survival rates of females of aphids Aphis gossypii up to the fifth generation. The longevity, reproductive period and amount of progeny were decreased in aphids treated with water suspension of fungal conidia. It can be deduced that the post-effect is caused by toxic action of metabolites as no evident mycosis was observed in the experiments. Similar type of after-effect is observed in the lacewing Chrysopa carnea contaminated with fungal conidia. The effect is also toxigenic being most prominent in the first generation of the survivors’ progeny and traceable up to the fifth generation. The consequences of the infection are best seen in the rate adult emergence which is twice as low as compared to control. This knowledge is essential to avoid antagonism between different groups of natural enemies exploited in biological control and to design adequate technology for their application.

Effects of fluorine-containing usnic acid and fungus Beauveria bassiana on the survival and immune-physiological reactions of Colorado potato beetle larvae

BACKGROUND

The search for compounds that interact synergistically with entomopathogenic fungi is aimed at enhancing the efficacy and stability of biological products against pest insects, for example, against the Colorado potato beetle (CPB). We hypothesized that fluorine-containing derivatives of usnic acid (FUA) might be candidates for the development of multicomponent bio-insecticides. The aim of this study was to analyze the co-influence of FUA and Beauveria bassiana on the survival and immune-physiological reactions of CPB larvae.

RESULTS

Synergy between FUA and B. bassiana was observed after treatment of second, third and fourth larvae instars under laboratory conditions. Furthermore, synergy was observed in field trials in continental climate conditions in southeastern Kazakhstan. In a field experiment, the median lethal time was shortened three-fold, and cumulative mortality for 15 days increased by 36% in the combined treatment compared with a fungal infection alone. FUA treatment delayed larval development, decreased the total hemocyte count, and increased both the phenoloxidase activity in integuments and the detoxification enzyme rate in hemolymph. A combined treatment with fungus and FUA led to increases in the aforementioned changes.

CONCLUSION

Toxicosis caused by FUA provides a stable synergistic effect between FUA and B. bassiana. The combination can be promising for the development of highly efficient products against CPB. © 2017 Society of Chemical Industry.

Scanning electron microscopy and histopathological observations of Beauveria bassiana infection of Colorado potato beetle larvae

Beauveria bassiana is a potential candidate for use as an environmentally friendly bio-pesticide. We studied the infection process and histopathology of B. bassiana strain NDBJJ-BFG infection of the Colorado potato beetle (Leptinotarsa decemlineata) using scanning electron microscopy and hematoxylin-eosin staining of tissue sections. The results show that the fungus penetrated the insect epidermis through germ tubes and appressoria after spraying the larvae with conidial suspensions. The conidia began to germinate after 24 h and invade the epidermis. After 48 h, the conidia invaded the larvae with germ tubes and began to enter the haemocoel. By 72 h, hyphae had covered the host surface and had colonized the body cavity. The dermal layer was dissolved, muscle tissues were ruptured and adipose tissue was removed. The mycelium had damaged the intestinal wall muscles, and invaded into intestinal wall and midfield cells resulting in cell separation and tracheal deformation. After 96 h of inoculation, the internal structure of the larvae was destroyed. The research shows that B. bassiana NDBJJ-BFG surface inoculation resulted in a series of histopathological changes to the potato beetle larvae that proved lethal within 72 h. This indicated that this fungus has a high pathogenicity to Colorado potato beetle larvae.

Ecological preferences of Metarhizium spp. from Russia and neighboring territories and their activity against Colorado potato beetle larvae

Thirty-four isolates of Metarhizium spp. from Russian collections were genotyped using 5' EF-1α gene sequence analysis. Four species were identified, of which M. robertsii and M. brunneum were the most frequent, whereas M. anisopliae and M. pemphigum were sporadic. Radial growth studies in the temperature range of 10-40°C revealed that growth at high temperatures (35-37.5°C) was inherent for M. robertsii isolates but not for M. brunneum isolates. In contrast, M. brunneum isolates were more active at cold temperatures (10°C) compared to M. robertsii. Virulence was evaluated against larvae of the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say, under two regimes: humid (21°C, 80% relative humidity (RH)) and arid (31°C, 55% RH). M. brunneum isolates were less virulent compared to M.robertsii under both regimes. M. robertsii activity did not differ under the two regimes, but M. brunneum was less virulent under the arid regime compared to the humid one. A field experiment under natural conditions (steppe zone of Western Siberia) with daily ranges of 10-43°C and 13-98% RH showed that M. robertsii was significantly more active than M. brunneum against CPB larvae.