Entomopathogenic fungi with biological control potential against poultry red mite (Dermanyssus gallinae, Arachnida: Dermanyssidae)

The poultry red mite, Dermanyssus gallinae (Arachnida: Dermanyssidae) is a pest that causes significant economic loss in laying hens for which control methods are limited. In this study, the effects of 20 indigenous fungal strains on poultry red mites in chicken farms were investigated. All experiments were conducted under laboratory condition at 28 ± 1 °C and 80 ± 5% humidity. A screening test showed that Metharizium flavoviride strain As-2 and Beauveria bassiana strain Pa4 had the greatest measured effect on D. gallinae at 1 × 107 conidia/ml 7 days after application. In a subsequent does-response experiment, these strains also caused 92.7% mortality at 1 × 109 conidia/ml within the same period. The LC50 of these strains was 5.5 × 104 (95% CI: 0.8-37.5) conidia/ml for As-2 and 3.2 × 104 (95% CI: 0.4-26.0) conidia/ml for Pa4, and their LT50 were 1.94 and 1.57 days, respectively. The commercial Metarhizium anisopliae bioinsecticide Bio-Storm 1.15% WP, used as a comparator, had LC50 and LT50 1 × 105 (95% CI: 0.1-7.9) conidia/ml and 3.03 (95% CI: 2.4-3.8) days, respectively. It is suggested that mycoacaricides could be developed using the best two fungal strains found in this study (As-2 and Pa4), providing potential for biological control of poultry red mites.

Isolation and identification of bacteria from the invasive pest Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) and evaluation of their biocontrol potential

As an alternative to chemical insecticides, gut bacteria of insects could be used to control insect pests. In this study, bacteria associated with Tuta absoluta, an invasive species that has developed resistance to chemical insecticides, were isolated, and their potential for pest control was investigated. We isolated 13 bacteria from larvae of the pest and identified the isolates on the basis of their morphological, physiological, biochemical, and molecular characteristics as Bacillus thuringiensis (Ta1-8), Staphylococcus petrasii (Ta9), Citrobacter freundii (Ta10), Chishuiella changwenlii (Ta11), Enterococcus casseliflavus (Ta12), and Pseudomonas tremae (Ta13). A laboratory screening test at 109 cfu/ml showed that B. thuringiensis (Bt) isolates caused more than 90% mortality after 3 days. Among the isolates, Bt-Ta1 showed the highest mortality in a short time. The LC50 and LC90 values for Bt-Ta1 were estimated to be 1.2 × 106 and 2 × 109 cfu/ml, respectively. Detailed characterization of Bt-Ta1 revealed that it is one of the serotypes effective on lepidopterans and contains the genes cry1Aa, cry2Aa, and vip3Aa, which encode lepidopteran toxic proteins. Bt-Ta1 isolate has been shown to have the potential to be used in the integrated management of Tuta absoluta.

Heliothis peltigera

This study reports a new Helicoverpa armigera nucleopolyhedrovirus (NPV) isolated from Heliothis peltigera (Denis & Schiffermuller), collected in the vicinity of Adana, Turkey. Infection was confirmed by tissue polymerase chain reaction and sequence analysis. Results showed that dead H. peltigera larvae contain Helicoverpa armigera nucleopolyhedrovirus. Thus, the isolate was named as HearNPV-TR. Microscopy studies indicated that occlusion bodies were 0.73 to 1.66 μm in diameter. The nucleocapsids are approximately 184 × 41 nm in size. The genome of HearNPV-TR was digested with KpnI and XhoI enzymes and calculated as 130.5 kb. Phylogenetic analysis showed that HearNPV-TR has close relation with the H. armigera SNPV-1073 China isolate. The Kimura analysis confirmed that the isolate is a variant of H. armigera NPV. Bioassays were performed using six different concentrations (1 × 10³ to 1 × 10⁸ occlusion bodies (OBs)/mL) on 2nd instar larvae of H. peltigera, H. armigera, Heliothis viriplaca, Heliothis nubigera. LC₅₀ values were calculated to be 9.5 × 10³, 1.9 × 10⁴, 8.6 × 10⁴ and 9.2 × 10⁴ OBs/mL within 14 days, respectively. Results showed that it is a promising biocontrol agent against Heliothinae species.

Microencapsulation of an indigenous isolate of Bacillus thuringiensis by spray drying

In this study, microencapsulation by spray drying was performed to protect spores and crystals of an indigenous isolate of Bacillus thuringiensis Se13 from environmental stress. The effects of wall material, inlet temperature, and outlet temperature on microencapsulation of Bt-Se13 were investigated using Taguchi's orthogonal array. The most suitable wall material determined as maltodextrin DE10. The optimum inlet and outlet temperatures of spray drier were determined as 160 °C and 70 °C, respectively. The number of viable spores, mean particle size, wetting time, percentage of suspensibility and moisture content of the product produced under optimum conditions were determined as 8.1 × 10¹¹ cfu g^-1, 13.462 µm, 25.22 s, 77.66% and 7.29%, respectively. As a result of efficiency studies on Spodoptera exigua in the laboratory conditions, the LC₅₀ was determined as 1.6 × 10⁴ cfu mL^-1. Microencapsulated Bt-Se13 based bio-pesticide may be registered for the control of S. exigua and can be tested against other lepidopterans which share the same environment.

Improvement of delta-endotoxin production from local Bacillus thuringiensis Se13 using Taguchi’s orthogonal array methodology

Objective

The insecticidal activity of Bacillus thuringiensis directly depends on the yield of delta-endotoxins. In this study, various nutritional and cultural parameters influencing delta-endotoxin synthesis by a local isolate of B. thuringiensis Se13 were investigated using Taguchi methods.

Methods

In the first experiment, four factors, incubation period, incubation temperature, initial pH and medium, each at four levels, were selected and an orthogonal array layout of L16 was carried out. In the second experiment, Taguchi’s orthogonal array method of L27 was used to evaluate the effects of the different concentration of medium components. Taguchi’s signal–noise ratio and variance analysis were applied to determine the effect of the factors. After each experiment, verification studies were carried out using determined optimum conditions.

Results

The optimum conditions for incubation period, incubation temperature, initial pH, and medium determined as 72 h, 30°C, pH 9, and M4 medium, respectively. In the second experiment, soybean flour (5%), glucose (5%), KH2PO4 (0.3%), K2HPO4 (0.1%), MgSO4 (0.4%) were determined as the optimum conditions. The delta-endotoxin yield was elevated to 1559.25 μg mL−1 when the factors were adjusted to optimum level.

Conclusion

Optimization using the Taguchi method appeared to be a good choice for the overproduction of delta-endotoxin.

Biodiversity and pathogenicity of bacteria associated with the gut microbiota of beet armyworm, Spodoptera exigua Hübner (Lepidoptera: Noctuidae)

In order to find an effective and environmentally friendly biocontrol agent against Spodoptera exigua, we isolated and identified a total of 15 different bacterial species belonging to phyla Firmicutes, Proteobacteria and Bacteroidetes. According to the phenotypic, genotypic and phylogenetic properties, bacterial isolates were identified as Bacillus cereus (Se1), Lysinibacillus macroides (Se2), Pseudomonas geniculata (Se3), Paenibacillus tylopili (Se4), Staphylococcus succinus (Se5), Acinetobacter soli (Se6), Chryseobacterium indologenes (Se7), Bacillus toyonensis (Se8), Serratia marcescens (Se9), Paenibacillus amylolyticus (Se10), Paenibacillus xylanexedens (Se11), Enterobacter ludwigii (Se12), Bacillus thuringiensis (Se13), Bacillus thuringiensis (Se14) and Lysinibacillus fusiformis (Se15). Screening of bacterial isolates for insecticidal potential was conducted at 10⁹ cfu ml^-1 bacterial concentration. The highest larvacidal effect was obtained with Bacillus thuringiensis Se13 with 100% mortality. In the dose response experiments performed with this bacterium, the median lethal concentration (LC₅₀) was estimated as 7.5 × 10⁴ cfu ml^-1 against 3rd instar larvae of the pest at 10 days post treatment. The median lethal time (LT₅₀) value of 10⁹ cfu ml^-1 bacterial concentration was also determined as 1.59 days. Phase-contrast and scanning electron microscope studies exhibited that B. thuringiensis Se13 produced different shape and size crystals (bipyramidal, cubic and spherical). Phylogenetic analysis of cry1 and cry2 gene content of this isolate displayed that B. thuringiensis Se13 had 99% homology with cry1Ac and cry2Aa, respectively. Finding from this study indicated that B. thuringiensis Se13 appears to be a promising microbial control agent for use against S. exigua.

A new biopesticide from a local Bacillus thuringiensis var. tenebrionis (Xd3) against alder leaf beetle (Coleoptera: Chrysomelidae)

Use of chemical pesticides in agriculture harms humans, non-target organisms and environments, and causes increase resistance against chemicals. In order to develop an effective bio-pesticide against coleopterans, particularly against Agelastica alni (Coleoptera: Chrysomelidae) which is one of the serious pests of alder leaf and hazelnut, we tested the insecticidal effect of 21 Bacillus isolates against the larvae and adults of the pest. Bacillus thuringiensis var. tenebrionis-Xd3 (Btt-Xd3) showed the highest insecticidal effect based on screening tests. For toxin protein production and high sporulation of Xd3, the most suitable medium, pH and temperature conditions were determined as nutrient broth medium enriched with salts, pH 7 and 30 °C, respectively. Sporulated Btt-Xd3 in nutrient broth medium enriched with salts transferred to fermentation medium containing soybean flour, glucose and salts. After fermentation, the mixture was dried in a spray dryer, and spore count of the powder product was determined as 1.6 × 10¹⁰ c.f.u. g^-1. Moisture content, suspensibility and wettability of the formulation were determined as 8.3, 86% and 21 s, respectively. Lethal concentrations (LC₅₀) of formulated Btt-Xd3 were determined as 0.15 × 10⁵ c.f.u. ml^-1 for larvae at laboratory conditions. LC₅₀ values were also determined as 0.45 × 10⁶ c.f.u. ml^-1 at the field condition on larval stage. Our results showed that a new bio-pesticide developed from B. thuringiensis tenebrionis (Xd3) (Btt-Xd3) may be valuable as a biological control agent for coleopteran pests.

Amsacta moorei entomopoxvirus encodes a functional esterase (amv133) with protease activity

OBJECTIVES

Lipolytic genes have been investigated in several viral genomes, and some of them show enzyme activity which can be used for various functions including the production of DNA replication metabolites, rescue from endosomes, and membrane fusion. Amsacta moorei entomopoxvirus (AMEV) replicates in nearly the entire insect body, especially in the adipose tissue. One of the open reading frames (ORFs) in the AMEV genome, amv133, encodes a putative lipase enzyme. In this study, we therefore investigate the enzyme activity of amv133.

METHODS

amv133 was aligned with known lipase genes and their homologs in entomopoxviruses. Expressed proteins were partially purified and assayed for lipase, esterase and protease.

RESULTS

We found that amv133 contains all the domains required for a functional lipase enzyme and that it shows a significant similarity with homologs in other entomopoxviruses. Since there is a similarity of the catalytic triad between lipases and serine proteases, we also investigated the protease activity of amv133. Lipase, esterase and protease assays showed that amv133 encodes a functional esterase enzyme with protease activity.

CONCLUSION

The current data show that amv133 is a conserved gene in all entomopoxvirus genomes sequenced so far and might contribute greatly to degrading the lipids or proteins and hence improve the virus infection.

Arthrobacter pityocampae sp. nov., isolated from Thaumetopoea pityocampa (Lep., Thaumetopoeidae)

A bacterium (strain Tp2(T)) was isolated from a caterpillar of the pine processionary moth, Thaumetopoea pityocampa (Den. & Schiff.) (Lepidoptera: Thaumetopoeidae), a destructive pine forest pest. The bacterium is a Gram-stain-positive, red-pigmented coccus, oxidase-negative, nitrate-reducing, non-motile and non-spore-forming. Strain Tp2(T) was subjected to a taxonomic study using polyphasic approach that included morphological and biochemical characterizations, 16S rRNA gene sequence analysis, DNA-DNA hybridization, DNA G+C content analysis, comparative fatty acid profiles, and analyses of quinones and polar lipids. The 16S rRNA gene sequence of strain Tp2(T) revealed that Arthrobacter agilis DSM 20550(T) was the closest known strain (98% 16S rRNA gene sequence similarity). DNA-DNA hybridization of A. agilis DSM 20550(T) and strain Tp2(T) resulted in a DNA-DNA relatedness value of 11.9% (20.2% reciprocal). The DNA base composition of strain Tp2(T) was 69.5 mol%, which is consistent with the other recognized members of Actinobacteria that have a high G+C content in their genome. The polar lipid pattern of strain Tp2(T) consisted of diphosphatidylglycerol (major), phosphatidylglycerol and phosphatidylinositol and unknown glycolipids. The cellular fatty acids were anteiso C15:0 and anteiso C17:0 and the major menaquinone was MK-9(II-H2). The peptidoglycan type was A3α with an L-Lys-L-Thr-L-Ala3 interpeptide bridge. The above-mentioned characterization qualifies strain Tp2(T) as genotypically and phenotypically distinct from closely related species of the genus Arthrobacter with validly published names. Strain Tp2(T) is therefore proposed to represent a novel species of the genus Arthrobacter, described as Arthrobacter pityocampae sp. nov. The type strain is Tp2(T) ( = DSM 21719(T) = NCCB 100254(T)).

A novel cry2Ab gene from the indigenous isolate Bacillus thuringiensis subsp. kurstaki

A novel cry2Ab gene was cloned and sequenced from the indigenous isolate of Bacillus thuringiensis subsp. kurstaki. This gene was designated as cry2Ab25 and its sequence revealed an open reading frame of 1,902 bp encoding a 633 aa protein with calculated molecular mass of 70 kDa and pI value of 8.98. The amino acid sequence of the Cry2Ab25 protein was compared with previously known Cry2Ab toxins, and the phylogenetic relationships among them were determined. The deduced amino acid sequence of the Cry2Ab25 protein showed 99% homology to the known Cry2Ab proteins, except for Cry2Ab10 and Cry2Ab12 with 97% homology, and a variation in one amino acid residue in comparison with all known Cry2Ab proteins. The cry2Ab25 gene was expressed in Escherichia coli BL21(DE3) cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed that the Cry2Ab25 protein is about 70 kDa. The toxin expressed in BL21(DE3) exhibited high toxicity against Malacosoma neustria and Rhagoletis cerasi with 73% and 75% mortality after 5 days of treatment, respectively.

Molecular characterization and virulence of Beauveria spp. from the pine processionary moth, Thaumetopoea pityocampa (Lepidoptera: Thaumetopoeidae)

The pine processionary moth Thaumetopoea pityocampa (Den. & Schiff.) is one of the most harmful pests to pine species in Mediterranean countries including Turkey. Caterpillars of T. pityocampa are not only significantly harmful to forest trees but also responsible for various allergic reactions in humans and animals. In this study, in order to find a more effective and safe biological control agent against T. pityocampa, we investigated fungal pathogens of T. pityocampa in the Black Sea Region of Turkey and tested their pathogenicity on it. Five different fungi were isolated and identified based on their morphological and molecular characteristics including ITS and partial sequence of EF1-[alpha]. Based on these characteristics, four isolates were identified as Beauveria bassiana cf. Clade C (Rehner and Buckley in Mycologia 97:84-98, 2005) and one isolate was identified as Beauveria bassiana. Among these isolates, B. bassiana KTU-24, B. bassiana cf. Clade C KTU-66 and KTU-67 showed the highest virulence with 100% mortality within 10 days after application. B. bassiana isolate KTU-24 produced the highest mycosis value with %100. Consequently, B. bassiana KTU-24 seems to be good candidate for further investigation as a possible biological control agent against this pest.

Brevibacterium pityocampae sp. nov., isolated from caterpillars of Thaumetopoea pityocampa (Lepidoptera, Thaumetopoeidae)

This work deals with the taxonomic study of a bacterium, strain Tp12T, isolated from caterpillars of the pine processionary moth (Thaumetopoea pityocampaDenis & Schiffermüller, 1775; Lepidoptera, Thaumetopoeidae). The isolate was assigned to the genusBrevibacteriumon the basis of a polyphasic taxonomic study, including morphological and biochemical characteristics, 16S rRNA gene sequence analysis, fatty acid analysis and DNA G+C content. The highest 16S rRNA gene sequence similarity to this isolate was approximately 96 %, with the type strains ofBrevibacterium albumandBrevibacterium samyangense. Cellular fatty acids of the isolate are of the branched type, with the major components being anteiso-C15 : 0and anteiso-C17 : 0. The DNA G+C content was 69.8 mol%. Although the strain was related toB. albumandB. samyangenseaccording to 16S rRNA gene sequence analysis, it differed from any known species ofBrevibacterium. Based on this evidence, the novel speciesBrevibacterium pityocampaesp. nov. is proposed, with strain Tp12T(=DSM 21720T=NCCB 100255T) as the type strain.

[Biology and replication of baculoviruses]

Baculoviruses have become a noteworthy research and study material for various applications in recent years. They are used as insecticides in agriculture because of their high host specifity. Recombinant baculoviruses are being used in biotechnology for the expression of related genes under the control of strong polh and p10 genes promoters. They have attracted attention as gene therapy vectors in medicine. Baculoviruses can enter the mammalian cells; however, they neither replicate nor show any pathogenic effect. Also baculoviruses are model organisms for molecular biology studies of gene structure and organization. Although baculoviruses are used commonly, their genome replication is not understood. Most of the research data about this subject have been obtained during recent years. Human beings have just begun to benefit from the use of baculoviruses. Baculoviruses will serve science in the future as mentioned above. We believe that this review will contribute to the appreciation of the field in our country in regard to baculoviruses which are popular all over the world. For this reason, in this review after giving information about the biology of baculoviruses, replication of baculoviruses has been explained in detail.

The Chilo iridescent virus DNA polymerase promoter contains an essential AAAAT motif

The delayed-early DNA polymerase promoter of Chilo iridescent virus (CIV), officially known as Invertebrate iridescent virus, was fine mapped by constructing a series of increasing deletions and by introducing point mutations. The effects of these mutations were examined in a luciferase reporter gene system using Bombyx mori cells transfected with promoter constructs and infected with CIV. When the size of the upstream element was reduced from position −19 to −15, relative to the transcriptional start site, the luciferase activity was reduced to almost zero. Point mutations showed that each of the 5 nt (AAAAT) located between –19 and –15 were equally essential for promoter activity. Mutations at individual bases around the transcription initiation site showed that the promoter extended until position −2 upstream of the transcription start site. South-Western analysis showed that a protein of approximately 100 kDa interacted with the −19 nt promoter fragment in CIV-infected cells. This binding did not occur with a point mutant that lacked promoter activity. The AAAAT motif was also found in the DNA polymerase promoter region of other iridoviruses and in other putative CIV delayed-early genes.

Characterization of a highly pathogenicBacillus thuringiensis strain isolated from common cockchafer,Melolontha melolontha

A bacterial isolate (Mm2) of Melolontha melolontha was identified and characterized. Based on various morphological, physiological, biochemical and molecular characteristics, it was identified as Bacillus thuringiensis subsp. tenebrionis. This isolate was compared to the reference strains by electron microscopy, SDS-PAGE analysis, plasmid pattern, cry gene content and insecticidal activity. Cells of the isolate harbored flat square inclusions containing a protein component of approximately equal to65 kDa. After trypsin digestion of solubilized crystals, SDS-PAGE resolved a unique proteinase-resistant peptide of approximately equal to 50 kDa. Plasmid pattern showed similar bands to those of the reference strain, PCR analysis showed that the isolate has cry3 gene. Toxicity tests (against 5 coleopteran species) showed 80 % insecticidal activity against the larvae of M. melolontha. The isolate Mm2 may be valuable as biological control agent for M. melolontha and other coleopteran insects.

Cry3Aa11: A New Cry3Aa δ-Endotoxin from a Local Isolate of Bacillus thuringiensis

A local isolate of Bacillus thuringiensis Mm2 had insecticidal activity against the larvae of Melolontha melolontha, Agelastica alni, Leptinotarsa decemlineata and Amphimallon solstitiale and produced a 65 kDa protein. SDS-PAGE profile of B. thuringiensis Mm2 was compared with those of 29 different Cry3Aa producers which verified Cry3Aa biosynthesis by the isolate. The cry3Aa gene of Mm2 was cloned, sequenced and the deduced amino acid sequence was compared with the cry3Aa sequences of ten different quaternary ranks. Its identity to these sequences ranged between 97.4% and 99.2%. The gene was next cloned into E. coli-Bacillus shuttle vector pNW33N and expressed at a low level in B. subtilis 168.

Isolation and insecticidal effects of some bacteria from Euproctis chrysorrhoea L. (Lepidoptera: Lymantriidae)

In this study, we investigated the bacterial pathogens of Euproctis chrysorrhoea and tested for their insecticidal activities. Based on colony color and morphology, four isolates were determined. According to morphological, physiological and biochemical characters of the isolates, they were identified as Enterobacter aerogenes, Lactobacillus sp., Bacillus thuringiensis and Micrococcus luteus. The insecticidal effects of these bacterial isolates on third-fourth instar larvae of Euproctis chrysorrhoea were investigated. The highest insecticidal effect determined on this pest is 68% with Bacillus thuringiensis. The effects of the other isolates are 45% with Enterobacter aerogenes, 15% Micrococcus luteus and 0% with Lactobacillus sp.