Construction and Selection of an Entomopathogenic Fungal Library From Soil Samples for Controlling Spodoptera litura

Abstract

Chemical pesticides have been used for pest control for many decades, but they cause serious problems, including insecticide resistance, secondary pest resurgence, and negative environmental impacts. Therefore, sustainable alternatives to chemical pesticides are necessary for pest control. Entomopathogenic fungi (EPF) are natural epizootic pathogens of insects, and some of them have been used as microbial biocontrol agents. Herein, we attempted to construct an entomopathogenic fungal library (EFLib) via the “Tenebrio molitor pathogenicity-based fungal collection method (TmPC)” to select EPF for control of the serious agricultural pest Spodoptera litura. A total of 172 soil samples were collected in northern and central Taiwan for the EFLib construction. The isolation efficiency of TmPC was 64.02%. The EFLib consisted of 101 isolates and was designated as the National Chung Hsing University (NCHU) EFLib. Among these isolates, 26 showed high virulence (mortality = 100%) to T. molitor larvae. Based on the results of molecular identification, the highly virulent isolates belonged to seven genera, including Beauveria, Clonostachys, Fusarium, Cordyceps, Penicillium, Purpureocillium, and Metarhizium. To evaluate the potential of these isolates for Spodoptera litura control, 12 isolates were selected for pathogenicity screening against S. litura larvae. A total of six EPF isolates belonging to the genera Beauveria and Metarhizium showed rapid eradication of the S. litura larvae. To rank the potential of these fungal strains for pest management, the six isolates were subjected to thermotolerance and conidial production assays, and a novel effective conidia number (ECN) formula was applied. The results indicated that the ECN index of Beauveria australis (NCHU-113) was much higher than that of Metarhizium isolates. However, among the Metarhizium isolates, NCHU-95 showed the highest ECN index. Altogether, NCHU-69 and NCHU-113 should be further tested in field trials. To our knowledge, this is the first attempt to integrate pathogenicity or virulence and ECN data into EPF screening and ranking, providing a baseline for mass selection of potential EPF strains for further applications.

Screening and Identification of Indigenous Entomopathogenic Fungal Isolates from Agricultural Farmland Soils in Nile Delta, Egypt

“…The insect baiting technique has been reported as a simple and effective tool for the isolation of insect associated EMPF from the soil [29,30] and DNA-based molecular characterization has become a standard approach for the accurate identification of microorganisms in this field [40]. Together they represent a pipeline for constructing collections of fungal isolates as essential step to develop microbial-based bioinsecticides as reported in numerous articles [13,41,42].…”

Effectiveness of Cordyceps sp. and Beauveria Bassiana Against Large Cabbage-heart Caterpillar, Crocidolomia Pavonana Fabricius (Lepidoptera: Crambidae)

“…Each treatment was repeated 5 times and every treatment were also sprayed on PDA plate using bacteriological agar (Bacto  ). After 24-96 hours, germinated conidia were counted under the microscope [10][11][12]14].…”

“…Conidia solution from each treatment was sprayed as much as 10 mL with a hand sprayer (volume 1 L) for each cabbage plant that had been infested with ten 3 rd instar larvae of C. pavonana. Each treatment was repeated 6 times, and spraying was carried out in the morning between 07.00 -09.00.Observation of dead larvae were carried out after 24 hours, and recorded for 6 days to calculated the percentage of cumulative mortality [12,14]. To prove that the dead C. pavonana larvae were caused by the fungus Cordyceps sp, the dead larvae were sterilized with 0.5% sodium hypochlorite for 5 minutes, then rinsed using sterile distilled water and inoculated on PDA media.…”

“…and Metharhizium anisopliae [9][10][11]. A study on molecular identification showed that seven genera of entomopathogenic fungi, namely Beauveria, Clonostachys, Cordyceps, Fusarium, Metarhizium, Penicillium, and Purpureocillium, had very high virulence [12]. Furthermore, the screening results from isolates of the genus Beauveria, and Metarhizium had high pathogenicity against Spodoptera litura [12].…”

“…A study on molecular identification showed that seven genera of entomopathogenic fungi, namely Beauveria, Clonostachys, Cordyceps, Fusarium, Metarhizium, Penicillium, and Purpureocillium, had very high virulence [12]. Furthermore, the screening results from isolates of the genus Beauveria, and Metarhizium had high pathogenicity against Spodoptera litura [12]. The results of another study showed that isolates of Beauveria bassiana, Isaria fumosorosea, Isaria sinclairii, Lecanicillium muscarium, Metarhizium rileyi, and at a concentration of 1 x 10 7 conidia mL -l were very effective in controlling the larvae of Plutela xylostella [11].…”