From waste to food and bioinsecticides: An innovative system integrating Tenebrio molitor bioconversion and pyrolysis bio-oil production.

To achieve a waste-free clean production, the present study aimed to valorize an underused agroindustrial byproduct (rice bran) by mealworms bioconversion and produce bio-oil from pyrolysis of insect excreta (frass) as bioinsecticide. To reach the first goal, the suitability of rice bran (RB) versus standard diet, wheat bran (WB), was examined by determining feed conversion, growth performance, and nutritional profile of T. molitor larvae. RB diet was an appropriate feed substrate for breeding mealworms, as evidenced by their high survival rates, optimal feed conversion parameters, and its capability to support the growth and life cycle of this insect. Besides, RB did not affect soluble larval protein content but modified crude fat content and fatty acid profile. In order to address the second aim, egested frass from RB and WB were subjected to pyrolysis to obtain bio-oils. The main compound was acetic acid (≈37%) followed by 1,6-anhydro-ß-d-glucopyranose (from 16 to 25%), as measured by GC-MS analysis. Nitrogen-containing chemicals accounted for ≈10%. Frass bio-oils could represent a novel source of bioinsecticides due to their bioeffectiveness in insect pests of economic importance (Plodia interpunctella and Tribolium castaneum) and medical interest (Culex pipiens pipiens). For P. interpunctella adults, frass bio-oils produced insecticidal activity by fumigant and contact exposure whereas for T. castaneum adults, just fumigant. By a miniaturized model that simulates semireal storage conditions, it was seen that, on T. castaneum, frass RB bio-oil generated higher repellent effect than frass WB. Finally, bio-oils proved to have larvicidal activity against Cx. p. pipiens.

Development and characterization of nanoemulsions loaded with essential oil and ß-cypermethrin and their bioefficacy on insect pest of economic and medical importance.

BACKGROUND: The development of novel and ecofriendly tools plays an important role in insect pest management. Nanoemulsions (NEs) based on essential oils (EOs) offer a safer alternative for human health and the environment. This study aimed to elaborate and evaluate the toxicological effects of NEs containing peppermint or palmarosa EOs combined with ß-cypermethrin (ß-CP) using ultrasound technique. RESULTS: The optimized ratio of active ingredients to surfactant was 1:2. The NEs containing peppermint EO combined with ß-CP (NEs peppermint/ß-CP) were polydisperse with two peaks at 12.77 nm (33.4% intensity) and 299.1 nm (66.6% intensity). However, the NEs containing palmarosa EO combined with ß-CP (NEs palmarosa/ß-CP) were monodisperse with a size of 104.5 nm. Both NEs were transparent and stable for 2 months. The insecticidal effect of NEs was evaluated against Tribolium castaneum and Sitophilus oryzae adults, as well as Culex pipiens pipiens larvae. On all these insects, NEs peppermint/ß-CP enhanced pyrethroid bioactivity from 4.22- to 16-folds while NEs palmarosa/ß-CP, from 3.90- to 10.6-folds. Moreover, both NEs maintained high insecticidal activities against all insects for 2 months, although a slight increase of the particle size was detected. CONCLUSION: The NEs elaborated in this work can be considered as highly promising formulations for the development of new insecticides. © 2023 Society of Chemical Industry.

Polymer nanoparticles containing essential oils: new options for mosquito control.

Mosquitoes (Diptera: Culicidae) are vectors of important parasites and pathogens causing death, poverty and social disability worldwide. The overuse of synthetic insecticides to control mosquito vectors lead to resistance, adverse environmental effects and high operational costs. Therefore, the development of eco-friendly control tools is an important public health challenge. In this study, two different essential oils (EO) (geranium, Geranium maculatum, and bergamot, Citrus bergamia) loaded polymeric nanoparticle (PN) were elaborated using polyethylene glycol (PEG) and chitosan (Qx) as the polymeric matrix/coating. In addition, the mosquito larvicidal acute and residual activity of the PN was evaluated on Culex pipiens pipiens. The physicochemical characterization of PN revealed that PEG-PN had sizes <255 nm and encapsulation efficiency between 68 and 77%; Qx-PN showed sizes <535 nm and encapsulation efficiency between 22 and 38%. From the toxicological test, it was observed that Qx-PN produced higher acute and residual activity than PEG-PN. Overall, this study highlights that polymer nanoparticles containing essential oil are a promising source of eco-friendly mosquito larvicidal products.

Design and development of aqueous nanoformulations for mosquito control.

Microemulsions (ME) are thermodynamically stable isotropic mixtures of oil, water, and surfactant; they would also be attractive as potential insecticidal products due to the high bioviability of the active ingredient, attributable to the small sizes of the oil drops. A laboratory study was conducted in order to compare the biological effect of oil in water (o/w) geranium essential oil (EO) and geraniol MEs and emulsions, against Culex pipiens pipiens mosquito larvae. The systems were based on three nonionic surfactants (Cremophor EL, Brij 35, Tween 80). The MEs showed dispersed phase diameters in the range of 8 to 14 nm and had low PDI values (<0.2). The MEs were analyzed by TEM, indicating that they had nearly spherical morphology. The microemulsified systems based on geranium EO and those of geraniol produced a notable increase of the larvicidal activity when compared with the respectably emulsions, concluding that the biological effect is related with the diameter of the dispersed phase. The smallest drops achieved the highest larvicidal activity, being the aqueous nanoformulations based on geraniol most effective than those of geranium EO. However, geranium microemulsions are preferred due to their residual toxicological profiles. The results indicate that these novel systems could be used in integrated pest management program for the C. pipiens pipiens.

Lethal and sublethal effects of four essential oils on the egg parasitoids Trissolcus basalis.

The essential oils from leaves of Schinus molle var. areira, Aloysia citriodora, Origanum vulgare and Thymus vulgaris have showed potential as phytoinsecticides against the green stink bug, Nezara viridula. In this work were evaluated their toxicological and behavioral effects on the parasitoid Trissolcus basalis, a biological control agent of this pest insect. Essential oils were obtained via hydrodestillation from fresh leaves. Insecticide activity in T. basalis females was evaluated in direct contact and fumigation bioassays. Behavioral effects were evaluated in olfactometer bioassays. To evaluate the residual toxicity, females of the parasitoids were exposed to oil residues; in these insects, the sublethal effects were evaluated (potential parasitism and survivorship of immature stages). The essential oils from O. vulgare and T. vulgaris proved to be highly selective when used as fumigant and did not change parasitoid behavior. After one week, the residues of these oils were harmless and did not show sublethal effects against T. basalis. According with these results, essential oils have potential applications for the integrated management of N. viridula.