Surf Redfish-Based ZnO-NPs and Their Biological Activity with Reference to Their Non-Target Toxicity.

The marine environment is a rich source of bioactive compounds. Therefore, the sea cucumber was isolated from the Red Sea at the Al-Ain Al-Sokhna coast and it was identified as surf redfish (Actinopyga mauritiana). The aqueous extract of the surf redfish was utilized as an ecofriendly, novel and sustainable approach to fabricate zinc oxide nanoparticles (ZnO-NPs). The biosynthesized ZnO-NPs were physico-chemically characterized and evaluated for their possible antibacterial and insecticidal activities. Additionally, their safety in the non-target organism model (Nile tilapia fish) was also investigated. ZnO-NPs were spherical with an average size of 24.69 ± 11.61 nm and had a peak at 350 nm as shown by TEM and UV-Vis, respectively. XRD analysis indicated a crystalline phase of ZnO-NPs with an average size of 21.7 nm. The FTIR pattern showed biological residues from the surf redfish extract, highlighting their potential role in the biosynthesis process. DLS indicated a negative zeta potential (-19.2 mV) of the ZnO-NPs which is a good preliminary indicator for their stability. ZnO-NPs showed larvicidal activity against mosquito Culex pipiens (LC50 = 15.412 ppm and LC90 = 52.745 ppm) and a potent adulticidal effect to the housefly Musca domestica (LD50 = 21.132 ppm and LD90 = 84.930 ppm). Tested concentrations of ZnO-NPs showed strong activity against the 3rd larval instar. Topical assays revealed dose-dependent adulticidal activity against M. domestica after 24 h of treatment with ZnO-NPs. ZnO-NPs presented a wide antibacterial activity against two fish-pathogen bacteria, Pseudomonas aeruginosa and Aeromonas hydrophila. Histopathological and hematological investigations of the non-target organism, Nile tilapia fish exposed to 75-600 ppm ZnO-NPs provide dose-dependent impacts. Overall, data highlighted the potential applications of surf redfish-mediated ZnO-NPs as an effective and safe way to control mosquitoes, houseflies and fish pathogenic bacteria.

Mosquitocidal Activity of the Methanolic Extract of Annickiachlorantha and Its Isolated Compounds against Culex pipiens, and Their Impact on the Non-Target Organism Zebrafish, Danio rerio.

In this study, the crude extract and its isolated compounds from the stem bark of Annickia chlorantha were tested for their larvicidal, developmental, and repellent activity against the mosquito vector, Culex pipiens, besides their toxicity to the non-target aquatic organism, the zebrafish (Danio rerio). The acute larvicidal activity of isolated compounds; namely, palmatine, jatrorrhizine, columbamine, ß-sitosterol, and Annickia chlorantha methanolic extract (AC), was observed. Developmentally, the larval duration was significantly prolonged when palmatine and ß-sitosterol were applied, whereas the pupal duration was significantly prolonged for almost all treatments except palmatine and jatrorrhizine, where it shortened from those in the control. Acetylcholinesterase (AChE) enzyme showed different activity patterns, where it significantly increased in columbamine and ß-sitosterol, and decreased in (AC), palmatine, and jatrorrhizine treatments, whereas glutathione S-transferase (GST) enzyme was significantly increased when AC methanolic extract/isolated compounds were applied, compared to the control. The adult emergence percentages were significantly decreased in all treatments, whereas tested compounds revealed non-significant (p > 0.05) changes in the sex ratio percentages, with a slight female-to-male preference presented in the AC-treated group. Additionally, the tested materials revealed repellence action; interestingly, palmatine and jatrorrhizine recorded higher levels of protection, followed by AC, columbamine, and ß-sitosterol for 7 consecutive hours compared to the negative and positive control groups. The non-target assay confirms that the tested materials have very low toxic activity compared to the reported toxicity against mosquito larvae. A docking simulation was employed to better understand the interaction of the isolated compounds with the enzymes, AChE and GST. Additionally, DFT calculations revealed that the reported larvicidal activity may be due to the differing electron distributions among tested compounds. Overall, this study highlights the potential of A. chlorantha extract and its isolated compounds as effective mosquitocidal agents with a very low toxic effect on non-target organisms.