Selection and characterization of Bacillus thuringiensis isolates with a high insecticidal activity against Spodoptera frugiperda (Lepidoptera: Noctuidae)

Abstract

Spodoptera frugiperda (SMITH, 1797) (Lepidoptera: Noctuidae) affects diverse crops of great economic interest, for instance, it can cause severe yield losses in maize, rice and sorghum. In this study, a selection and characterization of Bacillus thuringiensis (BERLINER, 1911) isolates with a high insecticidal activity against S. frugiperda was performed. Fifty-two crystal-forming B. thuringiensis isolates that were identified from 3384 Bacillus-like colonies were examined and screened by PCR for the presence cry genes (cry1, cry1Aa, cry1Ab, cry1Ac, cry1D, cry2 and cry2Ab). Four isolates that showed high toxicity towards S. frugiperda were shown to harbor cry2 genes. The crystals were analyzed by electron microscopy and showed bipyramidal and cuboidal shapes. Furthermore, these four isolates had lethal concentration (LC 50 ) values of 44.5 ng/cm 2 (SUFT01), 74.0 ng/cm 2 (SUFT02), 89.0 ng/cm 2 (SUFT03) and 108 ng/cm 2 (SUFT 04) to neonate S. frugiperda larvae. An ultrastructural analysis of midgut cells from S. frugiperda incubated with the SUFT01 spore-crystal complex showed disruptions in cellular integrity and in the microvilli of the midgut columnar cells. The isolates characterized in this work are good candidates for the control of S. frugiperda, and could be used for the formulation of new bioinsecticides.

Insecticidal activity of Bacillus thuringiensis strains isolated from tropical greenhouses towards Cydia pomonella and Spodoptera exigua larvae

“…These greenhouses are used to grow plants from the equatorial climate. The ratio of B. thuringiensis isolates comparing to all grown isolates noted in this work (~ 4%) was comparable to other reports, describing B. thuringiensis isolations from different geographic locations and various samples, where this value reached 1.5-5.0% (Berón and Salerno 2006;Ramalakshmi and Udayasuriyan 2010;Aramideh et al 2016;Cerqueira et al 2016;Lone et al 2017), but it was lower than in some other studies, showing that B. thuringiensis accounted for 10-60% of the isolates (Kim 2000;Apaydin et al 2005;Rabha et al 2017). Noteworthy is the fact that despite evident activity of BG11/BG12/BG15 strains against lepidopterans (they harbour genes encoding lepidopteran-active Cry1Ba/1Ia/2Ab/9Ea and Vip3Aa insecticidal proteins and were proven to be active against C. pomonella and S. exigua larvae), insects representing Lepidoptera order are not noted in the tropical greenhouses No.…”

Bacillus thuringiensis strains to control Noctuidae pests

“…Cry 1Ac represented 45.9% of 17 strains observed by Cerqueira et al. (2016), and Şahin et al. (2018) identified cry 1Ac in five isolates out of 80 strains.…”

“…The frequency of cry1Ac found in the present study is similar to the results observed byKaviyapriya et al (2019), who identified the presence of cry1Ac in strains producing high mortality levels on invasive lepidopterans pests. Cry1Ac represented 45.9% of 17 strains observed byCerqueira et al (2016), andŞahin et al (2018) identified cry1Ac in five isolates out of 80 strains.…”