• Mycobiology
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• v.43 no.2
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• pp.137-149
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• 2015

In the search for novel potent fungi-derived bioactive compounds for bioinsecticide applications, crude ethyl acetate culture filtrate extracts from 110 mangrove fungal endophytes were screened for their toxicity. Toxicity tests of all extracts against brine shrimp (Artemia salina) larvae were performed. The extracts with the highest toxicity were further examined for insecticidal activity against Spodoptera litura larvae and acetylcholinesterase (AChE) inhibition activity. The results showed that the extracts of five isolates exhibited the highest toxicity to brine shrimp at 50% lethal concentration ($LC_{50}$) values of 7.45 to 10.24 ppm. These five fungal isolates that obtained from Rhizophora mucronata were identified based on sequence data analysis of the internal transcribed spacer region of rDNA as Aspergillus oryzae (strain BPPTCC 6036), Emericella nidulans (strains BPPTCC 6035 and BPPTCC 6038), A. tamarii (strain BPPTCC 6037), and A. versicolor (strain BPPTCC 6039). The mean percentage of S. litura larval mortality following topical application of the five extracts ranged from 16.7% to 43.3%. In the AChE inhibition assay, the inhibition rates of the five extracts ranged from 40.7% to 48.9%, while eserine (positive control) had an inhibition rate of 96.8%, at a concentration of 100 ppm. The extracts used were crude extracts, so their potential as sources of AChE inhibition compounds makes them likely candidates as neurotoxins. The high-performance liquid chromatography profiles of the five extracts differed, indicating variations in their chemical constituents. This study highlights the potential of culture filtrate ethyl acetate extracts of mangrove fungal endophytes as a source of new potential bioactive compounds for bioinsecticide applications.

• Proceedings of the Korea Society of Environmental Toocicology Conference
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• 1996.12a
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• pp.70-70
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• 1996

The cytotoxicological effect of Bt 1-endotoxin, well-known as a bioinsecticide, was investigated on ion channel of insect cell lines. This study attempted to evaluted the specificity by simple experiment to measure the cell swelling using lepidopteran cell lines in isotonic solution containing only one cation. Cell swelling was stimulated in KCI-sucrose isotonic solution as well as TC-100 media containg in solubilized crystal 5-endotoxin. It suggested that the cell swelling by Bt toxin have a relation to K+ channel. The cell swelling may be due to the stimulation K+ influx and simultaneously the penetration of H2O induced by Bt toxin, because the stimulation of swelling was observed with the solubilized toxin in KCI-sucrose isotonic solution, but not in sucrose isotonic solution. Moreover the specific K+ channel blocker, such as 4-arnjnopyrimidine(4-AP) and ouabain, showed the significant effect on the cell swelling induced by Bt toxin. The increasement of the cell swelling induced by 4-AP suggested to be caused by the block of K+ efflux through K+ leak channels. The inhibition of cell swelling by ouabain, which is the well-known inhibitor of Na+, K+-ATPase, suggested to be due to decreasement of K+ influx following diminishment of Na+, K+-ATPase activities.

• Biotechnology and Bioprocess Engineering:BBE
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• v.4 no.1
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• pp.12-16
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• 1999

Xenorhabdus nematophilus sp., an insect-pathogenic bacterium, was newly isolated from Korean entomopathogenic nematode of Steinernema carpocapsae, which can be used as a useful bioinsecticide. Primary and secondary form variants of Xenorhabdus nematophilus were observed when cultured in vitro. Primary form variants adsorbed bromothymol blue, while secondary form did not. However, many other characters of two variants were very similar. The variants were all rod-shaped and cell size was highly variable ranging from 0.5 by 2.0 ${\mu}$m to 1.0 by 5.0 ${\mu}$m. Both produced highly toxic substances and killed the insect larva within 20∼38 hr, indicating that insect pathogenicity of Xenorhabdus is not directly associated with its phase variation. In addition, cell-free culture supernatant of Xenorhabdus was sufficient to kill the insect larva by injecting it ito insect hemolymph; however, cell-harboring culture broth was more effective for killing the insect. The use of Xenorhabdus nematophilus may provide a potential alternative to Bacillus thuringiensis (Bt) toxins.

• Korean journal of applied entomology
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• v.36 no.1
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• pp.37-42
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• 1997

Korean entomopathogenic fungi were serveryed from soil samples throughout the five provinces and within three city limits using larvae of great wax moth, Galleria mellonella as baits. The fungi were also isolated from the eight species of dead insects. Of the total 200 soil samples, 40(20.0%) were positive for entomopathogenic fungi with 21(10.5%) containing Beauveria and 19(9.5%) containing Metarhizium. Positive sample sites in each habitat included 25 of the 110(22.7%) from forests, 2 of the 20(11.0%) from agricultural fields, 6 of the 11(54.5%) from agricultural fallow areas, and 7 of the 19(36.8%) from riparian areas. In addition, Metarhizium was isolated from Japanese walking stick (Phraortes elongatus) and Beauveria from the other 7 species of dead insects.

• Journal of Applied Biological Chemistry
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• v.53 no.1
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• pp.21-24
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• 2010

In recent years, many agricultural scientists are studying on eco-friendly farming methods. Among of lots of the methods, the natural insecticides are highly motivated and interested due to their safety and biodegradable issues, and readily available source of bioinsecticides. In this study, the crude extract of custard apple (Annona reticulata L.) seed and its three fractions which were separated based on polarity indexes were examined for their insecticidal activities against Myzus persicae Sulzer and Nilaparvata lugens S.. The crude extract (Aceton/MeOH) showed strong insecticidal activities against both insects at 3.00 mg/mL ($LD_{50}$=0.45mg/mL for M. persicae S. and 1.42 mg/mL for N. lugens S.). Furthermore, simple fractionation with hexane, chloroform, and water lead to increase three-folds insecticidal activity on chloroform fraction ($LD_{50}$=0.13mg/mL for M. persicae S. and 1.14 mg/mL for N. lugens S.). The results suggest that A. reticulata extracts might be used to control for M. persicae effectively.

• Journal of Sericultural and Entomological Science
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• v.51 no.2
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• pp.137-141
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• 2013

In this study, nucleotide sequence structures of intergenic transcribed spacer (ITS) 1, complete 5.8S ribosomal RNA gene and ITS 2 region were analyzed to identify three Peruvian entomopathogenic fungal isolates. The isolates had highly conserved sequence region in 5.8S rRNA gene and unique sequences in ITS 1 and 2 region among them. 5.8S rRNA gene regions were highly conserved and showed high homoloies among tested isolates. In contrast, ITS region showed species-specific sequence region, resulting in inter-genus differencies. Scanning electron microscopic images of these isolates supported the result of ITS-based identification. From these result, Peruvian entomopathogenic fungal isolate J270, J278, were identified as Beauveria bassiana and J271 was identified as Lecanicillium attenuatum.