Histopathology and the lethal effect of Cry proteins and strains of Bacillus thuringiensis Berliner in Spodoptera frugiperda J.E. Smith Caterpillars (Lepidoptera, Noctuidae)

Abstract

Among the phytophagous insects which attack crops, the fall armyworm, Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera, Noctuidae) is particularly harmful in the initial growth phase of rice plants. As a potential means of controlling this pest, and considering that the entomopathogen Bacillus thuringiensis Berliner demonstrates toxicity due to synthesis of the Cry protein, the present study was undertaken to evaluate this toxic effect of B. thuringiensis thuringiensis 407 (pH 408) and B. thuringiensis kurstaki HD-73 on S. frugiperda. The following method was used. Both bacterial strains were evaluated in vitro in 1 st instar S. frugiperda caterpillars, by means of histopathological assays. The Cry1Ab and Cry1Ac proteins, codified by the respective strains of B. thuringiensis, were evaluated in vivo by bioassays of 1 st instar S. frugiperda caterpillars in order to determine the Mean Lethal Concentration (LC 50 ). The results of the histopathological analysis of the midget of S. frugiperda caterpillars demonstrate that treatment with the B. thuringiensis thuringiensis strain was more efficient, because the degradations of the microvilosities started 9 hours after treatment application (HAT), while in the B. thuringiensis kurstaki the same effect was noticed only after 12 HAT. Toxicity data of the Cry1Ab and Cry1Ac proteins presented for the target-species LC 50 levels of 9.29 and 1.79 µg.cm , respectivamente. As cepas e proteínas sintetizadas por B. thuringiensis thuringiensis e B. thuringiensis kurstaki são eficientes no controle de S. frugiperda, e poderão ser usadas na produção de novos biopesticidas ou a utilização dos genes na transformação genética de Oryza sativa L. Histopatologia e efeito letal de cepas e proteínas Cry de Bacillus thuringiensis

Two new Brazilian isolates of Bacillus thuringiensis toxic to Anticarsia gemmatalis (Lepidoptera: Noctuidae)

“…Several studies aiming to evaluate new B. thuringiensis strains against lepidopterans have been performed worldwide (Zhong et al 2000;Uribe, et al 2003;Polanczyk et al, 2003;Knaak et al 2010). Despite the mode of action of this pathogen showing similarity to all Lepidoptera, the discovery of new B. thuringiensis strains becomes important to study specific toxicity to target insects.…”

“…After solubilisation, the protoxins are activated by intestinal proteases, yielding the activated form of Cry toxins. Then, the toxins bind to receptors of high affinity sites on the surface of epithelial cells of the midgut microvilli, which are turgid and burst due to formation of pores in the apical membranes (Grochulski et al, 1995;Bravo et al, 2004;Fiuza, 2004;Knaak et al, 2010).…”

Mode of Action and Specificity of Bacillus thuringiensis Toxins in the Control of Caterpillars and Stink Bugs in Soybean Culture

“…This destroys the microvilli, causing the insect to stop feeding, leading to its death [7, 23, 76, 89, 90]. …”

Toxicology of the Bioinsecticides Used in Agricultural Food Production

“…Several studies report on the cell changes produced in the middle intestine of caterpillars intoxicated with Cry proteins from B. thuringiensis -for example: the increase in the volume of the epithelium cells, the rupture of the microvilli, cytoplasmic vacuolization, the changes in cytoplasmic organelles and cell hypertrophy (30,(33)(34)(35).…”