Bioactivity of Bacillus thuringiensis (Bacillales: Bacillaceae) on Diatraea saccharalis (Lepidoptera: Crambidae) eggs

Abstract

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

Potential of Two <i>Metarhizium anisopliae</i> (Clavicipitaceae) Isolates for Biological Control of <i>Diatraea saccharalis</i> (Lepidoptera: Crambidae) Eggs

“…This result is superior to the inviability potential of Blissus Antilles (Hemiptera: Lygaeidae) eggs (24-h old) infected by the ESALQ818 isolate (10 4 conidia/mL), at 96.7% [40]. Other studies have evaluated the mortality of D. saccharalis eggs treated with different solutions: Daquila et al [32] observed 34.98% inviability in eggs (0 -24-h old) infected by Bacillus thuringiensis isolate Aizawai GC-91 (Bacillales: Bacillaceae) and Canazart et al [31] observed that the alternative control with garlic essential oil (0.5%) made more than 60% of the eggs unfeasible.…”

“…The chorion of D. saccharalis eggs has a thin and translucid structure [31], formed by two structures, the exochorion and endochorion [32]. These structures are synthesized by ovarian follicular cells [46].…”

“…The glycogen (yolk) is crucial for embryonic development. Therefore, toxins in the yolk may interrupt or inhibit the embryonic development of D. saccharalis eggs [32]. The presence of energids indicates the beginning of embryonic development; however, this process is interrupted by the toxins released by fungal hyphae.…”

Selectivity ofBacillus thuringiensis(Bacillales: Bacillaceae) to the polyphagous predatorCeraeochrysa claveri(Navás, 1911) (Neuroptera: Chrysopidae)

“…Four concentrations (0.62, 1.25, 2.50 and 5.00 g L −1 ) were obtained after diluting the commercial product in autoclaved distilled water at a temperature of 25°C and pH 7.0. The concentrations were based on Daquila et al (2021) for the control of D. saccharalis eggs, which is an insect pest that can be a prey for lacewings in sugarcane crops.…”

More to legs than meets the eye: Presence and function of pheromone compounds on heliothine moth legs

“…Since chemicals from legs may be deposited at oviposition sites, we additionally hypothesised that they may protect eggs against microbial threats. Microbial infections reduce moth egg viability (Daquila et al, 2021; Hajek et al, 1996; Sikorowski et al, 2001; Tanabe & Tamashiro, 1967). Chemicals from moth legs could disinfect surfaces to prevent microbial growth.…”