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Biocontrol competence of Beauveria bassiana, Metarhizium anisopliae and Bacillus thuringiensis against tomato leaf miner, Tuta absoluta Meyrick 1917 under greenhouse and field conditions.

ABSTRACT: Tomato is one of the most important crops grown under both greenhouse and field conditions throughout the world. Its production is highly challenged by infestation of leaf miner insect, Tuta absoluta Meyrick regardless of excessive insecticide application. The chemical insecticides results insect resistance, environmental pollution, and health problems and there is urgent need for management options such as integrated pest management (IPM) to obviate these problems. Thus, the present study aims to evaluate the effectiveness of single and combination treatments of entomopathogens; Beauveria bassiana, Metarhizium anisopliae, Bacillus thuringeinsis, and an insecticide against T. absoluta under greenhouse and field conditions. Two varieties (Awash and Venes) of tomato for greenhouse experiment and one (Gellila) variety for field experiment were used with Tutan36%SC (insecticide with active ingredient of Chlorphenapyr 36%SC) and untreated plots as positive and negative controls, respectively. The results showed significant leaf and fruit damage reduction in all the treatments. B. bassiana-AAUB03, M. anisopliae-AAUM78, and B. thuringiensis-AAUF6 showed the highest (93.4%, 89.7% and 90.1%) leaf and (93.5%, 94.4% and 95%) fruit protection under greenhouse condition. The combined treatments improved leaf protection efficacy up to 95.3% under field condition. When the entomopathogens were combined with half or quarter reduced concentrations of Tutan36% SC, it showed 94.4% of pest protection. In all the treatments, 72-96% of marketable fruit was obtained as par insecticide treatment scored 85-93%. All the entomopathogens did not cause any adverse effect on the growth of tomato rather improved shoot length, shoot branching, leaf and fruit numbers. Therefore, application of entomopathogens in single, consortium or in combination reduced the recommended concentration of Tutan36%SC to control T. absoluta.

SUBMITTER: Aynalem B

PROVIDER: S-EPMC9213718 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundTuta absoluta Meyrick 1917 (Lepidoptera: Gelechiidae) is an invasive, pesticide resistant, and a major treat of tomato production in the world. It needs effective management options that naturally infect the insect without causing any identified side effects. Entomopathogenic fungi (EPF) are the most important options. However, geographic origin and climatic condition apparently creates genetic variation among EPF strains that influence on their pathogenicity. Thus, screening of effective EPF strains from the local source is vital to develop environmental friendly pest control tactic for T. absoluta.ResultsIn this study, 27 indigenous Beauveria were isolated from the various types of soil and 12 of the isolates were screened based on their biological efficiency index (BEI). These isolates scored 65.7-95.7% and 68.3-95% of mortality against second and third instar larvae of T. absoluta at concentration of 1 × 107spores·ml-1 in 7 days post inoculation, respectively. Out of these, five (18.5%) isolates scored above 90% mortality on both instar larvae with LT50 value of 3.33 to 5.33 days at the lowest (104 spores·ml-1) and 1.93 to 3.17 days at highest (108 spores·ml-1) spore concentrations and has LC50 value of 1.5 × 103 to 1.1× 105 spores·ml-1. Moreover, isolates exhibited the promising mortality better (1.5 × 106 to 3.5 × 107 spores·ml-1), sporulated over the larval cadavers, well grown at optimal temperature, and produced chitinolytic enzymes. Molecular analysis showed that isolates have nearly monophyletic characters and grouped under species of Beauveria bassiana.ConclusionDifferent types of soil in Ethiopia are an important source of B. bassiana, and these isolates showed promising pathogenicity against T. absoluta, which is crucial for ecofriendly biopesticide development. Although isolates were nearly monophyletic in phylogenetic study, five of them were highly effective in the laboratory bioassays against T. absoluta; however, further field evaluation is required for mass production.

Project description:Tomato (Solanum esculentum) is one of the vegetable crops grown by both smallholder and commercial farmers in the Kingdom of Eswatini. Tomato leaf miner, Tuta absoluta M. is a major insect pest of tomatoes resulting in reduced tomato yields throughout the country. The study investigated the virulence of two sub-tropical EPN species on T. absoluta larvae. Steinernema yirgalemense and S. jeffreyense at different concentrations (0, 20, 40, 60 IJs/insect) were screened for efficacy (i.e. mortality rate) against larvae of T. absoluta in laboratory bioassays. Results obtained showed that S. yirgalemense and S. jeffreyense were able to kill T. absoluta larvae without significant differences between the two EPN species in 24-well bioassay trays. Significantly higher (p < 0.05) mortality was observed when 60 IJs/insect was used. The combination of S. yirgalemense at 60 IJs/insect (100%) and S. jeffreyense at 60 IJs/insect (98.3%) resulted in significantly higher (p < 0.05) mortality, compared with the other four combinations of EPN and concentration tested. In the leaf bioassays, S. yirgalemense (58.8%) resulted in significantly higher (p < 0.05) mean mortality compared to S. jeffreyense (46.4%). Steinernema yirgalemense at 60 IJs/insect resulted in significantly higher mean mortality compared to the other EPN and concentration combinations in the leaf bioassay. The results indicated that both EPNs tested were effective against T. absoluta larvae. Steinernema yirgalemense at 60 IJs/insect can effectively find T. absoluta larvae inside leaf mines, but large-scale field trials are recommended to demonstrate the potential use of the biocontrol agent within integrated pest management programs.Tomato (Solanum esculentum) is one of the vegetable crops grown by both smallholder and commercial farmers in the Kingdom of Eswatini. Tomato leaf miner, Tuta absoluta M. is a major insect pest of tomatoes resulting in reduced tomato yields throughout the country. The study investigated the virulence of two sub-tropical EPN species on T. absoluta larvae. Steinernema yirgalemense and S. jeffreyense at different concentrations (0, 20, 40, 60 IJs/insect) were screened for efficacy (i.e. mortality rate) against larvae of T. absoluta in laboratory bioassays. Results obtained showed that S. yirgalemense and S. jeffreyense were able to kill T. absoluta larvae without significant differences between the two EPN species in 24-well bioassay trays. Significantly higher (p < 0.05) mortality was observed when 60 IJs/insect was used. The combination of S. yirgalemense at 60 IJs/insect (100%) and S. jeffreyense at 60 IJs/insect (98.3%) resulted in significantly higher (p < 0.05) mortality, compared with the other four combinations of EPN and concentration tested. In the leaf bioassays, S. yirgalemense (58.8%) resulted in significantly higher (p < 0.05) mean mortality compared to S. jeffreyense (46.4%). Steinernema yirgalemense at 60 IJs/insect resulted in significantly higher mean mortality compared to the other EPN and concentration combinations in the leaf bioassay. The results indicated that both EPNs tested were effective against T. absoluta larvae. Steinernema yirgalemense at 60 IJs/insect can effectively find T. absoluta larvae inside leaf mines, but large-scale field trials are recommended to demonstrate the potential use of the biocontrol agent within integrated pest management programs.

Project description:Tuta absoluta (the tomato pinworm) is an invasive insect pest with a highly damaging effect on tomatoes causing between 80 and 100% yield losses if left uncontrolled. Resistance to chemical pesticides have been reported in some T. absoluta populations. Insect microbiome plays an important role in the behavior, physiology, and survivability of their host. In a bid to explore and develop an alternative control method, the associated microbiome of this insect was studied. In this study, we unraveled the bacterial biota of T. absoluta larvae and adults by sequencing and analyzing the 16S rRNA V3-V4 gene regions using Illumina NovaSeq PE250. Out of 2,092,015 amplicon sequence variants (ASVs) recovered from 30 samples (15 larvae and 15 adults), 1,268,810 and 823,205 ASVs were obtained from the larvae and adults, respectively. A total of 433 bacterial genera were shared between the adults and larval samples while 264 and 139 genera were unique to the larvae and adults, respectively. Amplicon metagenomic analyses of the sequences showed the dominance of the phylum Proteobacteria in the adult samples while Firmicutes and Proteobacteria dominated in the larval samples. Linear discriminant analysis effect size (LEfSe) comparison revealed the genera Pseudomonas, Delftia and Ralstonia to be differentially enriched in the adult samples while Enterococcus, Enterobacter, Lactococcus, Klebsiella and Wiessella were differentially abundant in the larvae. The diversity indices showed that the bacterial communities were not different between the insect samples collected from different geographical regions. However, the bacterial communities significantly differed based on the sample type between larvae and adults. A co-occurrence network of significantly correlated taxa revealed a strong interaction between the microbial communities. The functional analysis of the microbiome using FAPROTAX showed that denitrification, arsenite oxidation, methylotrophy and methanotrophy as the active functional groups of the adult and larvae microbiomes. Our results have revealed the core taxonomic, functional, and interacting microbiota of T. absoluta and these indicate that the larvae and adults harbor a similar but transitory set of bacteria. The results provide a novel insight and a basis for exploring microbiome-based biocontrol strategy for this invasive insect pest as well as the ecological significance of some of the identified microbiota is discussed.

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Biocontrol competence of Beauveria bassiana, Metarhizium anisopliae and Bacillus thuringiensis against tomato leaf miner, Tuta absoluta Meyrick 1917 under greenhouse and field conditions.

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