Rolliniastatin-1, a bis-tetrahydrofuran acetogenin: The major compound of Annona mucosa Jacq. (Annonaceae) has potent grain-protective properties

Highlights

• Bioassay-guided fractionations with derivatives prepared from Annona mucosa seeds were performed.

• The acetogenin bis-tetrahydrofuran rolliniastatin-1 was identified as major bioactive constituent.

• This compound promoted significant mortality of exposed weevils, drastically reducing F₁ progeny and their damage to corn grains.

• Rolliniastatin-1 protected grain statistically similar to that of a diatomaceous-earth based formulation.

Abstract

The widespread use of synthetic insecticides results in insecticide-resistant populations of maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae), a primary pest species of stored corn worldwide. Thus, new active ingredients with different modes of action are needed for integrated pest management (IPM) of stored grains. Thus, toxicological bioassays (using S. zeamais as bioindicator) associated to chromatographic techniques were performed to isolate insecticidal compounds from the grain-protective ethanolic extract of Annona mucosa Jacq. (Annonaceae) seeds. The acetogenin bis-tetrahydrofuran rolliniastatin-1 was identified as major bioactive constituent from A. mucosa seeds based on bioassay-guided fractionation, along with rolliniastatin-2, deethylrollinastatin-1, jimenezin and fractions containing triglycerides. This compound produced 51.1% of mortality of adult weevils when applied at 57.66 mg kg⁻¹, drastically reducing F₁ progeny and their damage to corn grains. Although the acute toxicity level was lower than that with the formulation based on diatomaceous earth at a concentration 17.3 times higher (Insecto®^, at recommended rate) used as a positive control, rolliniastatin-1 protected grain statistically similar to that of the positive control. Furthermore, bioassays indicate that compounds of different chemical natures have a synergistic effect on the overall biological activity of seed derivatives of A. mucosa. Efficacy and technical viability of the process to obtain rolliniastatin-1 from the seeds of A. mucosa should allow the production of a botanical insecticide to control populations of S. zeamais at corn warehouses.

Introduction

The risk of selecting insecticide-resistant populations poses as a major challenge for integrated pest management (IPM) programs of stored cereals in tropical and subtropical regions. In South America, studies have described populations of maize weevil [Sitophilus zeamais Motsch. (Coleoptera: Curculionidae)] resistant to pyrethroids (Guedes et al., 1995; Corrêa et al., 2011; Cordeiro et al., 2017), organophosphates (Perez-Mendoza, 1999; Corrêa et al., 2011) and phosphine (Pimentel et al., 2009; Corrêa et al., 2014). The limited availability of active ingredients for insecticide rotation in IPM programs of stored cereals aggravates the risk of selecting insecticide-resistant populations of S. zeamais (Boyer et al., 2012). Thus, new compounds with different modes of action are needed for IPM of stored grains.

A potential source of new insecticidal compounds are the secondary metabolites of Annonaceae species, which produce and accumulate acetogenins in abundance, mainly in their seeds (Chen et al., 2012; González-Esquinca et al., 2014). Acetogenins are a class of compounds derived from long-chain fatty acids (C-32/C-34) connected to a 2-propanol unit and γ-lactone subunit (Alali et al., 1999). Acetogenins have insecticidal action and are inhibitors of mitochondrial complex I (Tormo et al., 1999). The botanical family Annonaceae encompasses a wide number of tree and shrub species, mostly native to tropical and subtropical regions, which produce edible fruits used in the food industry (Maas, 2009, 2013; Braga Sobrinho, 2014). Waste seed from Annona fruits could be used as raw material for acetogenin-based bioinsecticide production (Ribeiro et al., 2016). Bioinsecticides formulated from agro-industrial residues are a great opportunity to transform environmental problems into eco-friendly solutions for agriculture.

In addition, an advantage of acetogenin-based bioinsecticides in the global pest management market is their suitability for organic farming. Organic farming is constantly increasing worldwide and needs eco-friendly alternatives for pest management. Roughly 57.8 million hectares are cropped using organic farming, integrating a market of US$ 87.9 billion worldwide (Willer and Lernoud, 2019). Because of their chemical nature, acetogenin-based bioinsecticides could be used in the preventative management of coleopteran pests in stored organic cereals, as Ribeiro et al. (2018) demonstrated using an acetogenin-based commercial bioinsecticide registered in India.

In our previous studies, we reported the promising grain-protective properties of crude extracts from Annona mucosa Jacq. seeds against the maize weevil (Ribeiro et al., 2013), with a crude derivative from this species the most promising source of grain protectants (LC₅₀: 288.3 mg kg⁻¹; LT₅₀: 86.1 h) among the tested neotropical Annonaceae (Ribeiro et al., 2016). Annona-based bioinsecticides have pronounced lethal and sublethal effects on agricultural insect pests, such as Diaphorina citri Kuwayama (Hemiptera: Liviidae) (Ribeiro et al., 2015), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) (Ansante et al., 2015), Zaprionus indianus (Gupta) (Diptera: Drosophilidae) (Geisler et al., 2019), Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) (Stupp et al., 2020a), and Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) (Stupp et al., 2020b). However, formulation of a botanical insecticide requires identification and establishment of minimum concentrations of active ingredients as well as identification of a chemical marker for quality control of formulations. Moreover, isolation and elucidation of chemical structures of active compounds can contribute to the synthesis of natural-derived insecticides that are more acceptable by farmers and consumers (Domingues et al., 2020).

Therefore, we conducted bioassay-guided chromatographic fractionations to isolate, purify and characterize grain-protective acetogenin(s) from A. mucosa seeds against the maize weevil, a primary pest of stored corn worldwide. The activity of isolated acetogenin was compared with a diatomaceous earth-based formulation (Insecto®) used as positive control.