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BACKGROUND Bacillus thuringiensis (Bt) is a Gram‐positive bacterium that synthesizes specific protein toxins, which can be exploited for control of various insect pests, including Diatraea saccharalis, a lepidopteran that severely damages sugarcane crops. Although studies have described the effects of Bt in the larval phases of D. saccharalis, few have examined its effect on insect eggs. Herein, we studied the entomopathogenic potential of Bacillus thuringiensis serovar Aizawai GC‐91 (Bta) during D. saccharalis embryo development with the aim of understanding the entomopathogenic mechanism and developing new biological control techniques for target insects. RESULTS Bta concentrations of 5, 10 and 20 g L–1 demonstrated the strongest bioactivity, reducing D. saccharalis egg viability by 28.69%, 33.91% and 34.98%, respectively. The lethal concentrations (LCs) were estimated as: LC50 = 28.07 g L–1 (CI 95% = 1.89–2.38) and LC90 = 65.36 g L–1 (CI 95% = 4.19–5.26). Alterations in egg coloration, melanization and granule accumulation were observed at 24 h, persisting until 144 h. The embryo digestive systems were severely damaged, including narrowing of the intestinal lumen, vesiculations and degenerated cells, causing embryonic death. CONCLUSION The toxicity caused by Bta in D. saccharalis embryos demonstrated its potential as a biological control agent and as a sustainable alternative for integrated management of D. saccharalis infestation. © 2020 Society of Chemical Industry

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Studies have reported the resurgence of insect pests that are resistant to chemical and, more recently, to biological pesticides. Diatraea saccharalis is one of the main pests in sugarcane crops and responsible for large losses in the sugar and alcohol industries. The use of plant extracts including garlic essential oil (Allium sativum) which contains allicin, a compound that interferes with biochemical and physiological factors of target insects is considered an efficient and sustainable alternative for integrated pest management. The objective of this study was to test the toxicity of garlic essential oil on D. saccharalis eggs by analyzing rates of unhatched eggs, changes in external morphology, and esterases profile, enzymes related to insect resistance. For this, 24, 48, and 72-h-old eggs were immersed in 0.1, 0.5, and 1% garlic essential oil solutions for 2 min. Observations on embryonic development were made every 24-h for 72-h. Data on unhatched eggs were collected 288-h after treatments. For the esterases profile, eggs at 24-h after treatment with 1% solution were used. Eggs at 24-h-old, showed the least resistance to bioinsecticide, being that, 24-h after treatments with solutions 0.1, 0.5, and 1%, unhatched rates 80, 91.7, and 89.2%, respectively. The absence of embryos, ruptures, and protrusions on the chorionic region, and partial inhibition of EST-9, 10, and 11 were observed 24-h after the bioassays. These results demonstrate that garlic essential oil affects D. saccharalis eggs, partially inhibiting enzymes related to the insect immune system and can be used as a sustainable alternative for the integrated management of this insect pest.

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Biopesticides based on Bacillus thuringiensis (Bt) are widely used to control agricultural pests. These products are efficient and have high specificity to target insects. However, there are concerns about their impact on non-target organisms. Ceraeochrysa claveri, is a polyphagous predator with important value in the biological control of insect pests in crops of economic interest. This study aimed to analyze the effects of B. thuringiensis serovar aizawai CG-91 (Bta) on the post-embryonic development of C. claveri. Neonate larvae of C. claveri were fed with Diatraea saccharalis eggs contaminated with different concentrations of Bta (0.62, 1.25, 2.50, and 5.00 g.L-1) until your pupation. Samples of the midgut larvae were collected for histological and ultrastructural analysis, and the larval and pupal inviability data were collected at the end of the respective developmental stages. After the emergence of adult insects, were considered inviable those with morphological alterations. To evaluate the reproduction, adult insects couples were formed, and the oviposition was collecteds. No significant differences in the viability of eggs, larvae, pupae, and adults of C. claveri contaminated with Bta were reported. Midgut analyses did not reveal cellular damage in the epithelium, indicating a possible lack of insecticidal proteins receptors. The oviposition and their viability were similar between treated and control groups. Our results demonstrated that Bta did not affect the post-embryonic development of C. claveri. This illustrates that the combined use of Bta and C. claveri for the biological control of arthropod pests can be a sustainable strategy for integrated pest management.

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