New prospective insecticidal agents based on thiazolo[4,5-b]quinoxaline derivatives against cotton leafworm Spodoptera litura (Fabricius): Design, synthesis, toxicological, morphology, histological, and biomedical studies.

In this study, a new series of thiazolo[4,5-b]quinoxaline derivatives 3-8 were synthesized by treating 2,3-dichloroquinoxaline with thiosemicarbazone and thiourea derivatives under reflux conditions. The chemical structure of the newly designed derivatives was conducted using spectroscopic techniques. The insecticidal bioassay of the designed derivatives was evaluated against the 2nd and 4th larvae of S. litura after five days as toxicity agents via median lethal concentration (LC50) and the lethal time values (LT50). The results indicated that all the tested compounds had insecticidal effects against both instar larvae of S. litura with variable values. Among them, thiazolo[4,5-b]quinoxaline derivative 3 was the most toxic, with LC50 = 261.88 and 433.68 ppm against 2nd and 4th instar larvae, respectively. Moreover, the thiazolo[4,5-b]quinoxaline derivative 3 required the least time to kill the 50% population (LT50) of 2nd larvae were 20.88, 13.2, and 15.84 hs with 625, 1250, and 2500 ppm, respectively, while for the 4th larval instar were 2.75, 2.08, and 1.76 days with concentrations of 625, 1250, and 2500 ppm, respectively. Larvae's morphological and histological studies for the most active derivative 3 were investigated. According to SEM analysis, the exterior morphology of the cuticle and head capsule was affected. In addition, there were some histological alterations in the cuticle layers and the midgut tissues. Columnar cells began breaking down, and vacuolization occurred in the peritrophic membrane. Moreover, treating 4th S litura larvae hemolymph with compound 3 showed significant changes in biochemical analysis, such as total proteins, GPT, GOT, acetylcholinesterase (AChE), and alkaline phosphatase (AlP). Finally, the toxicity prediction of the most active derivative revealed non-corrosive, non-irritant to the eye, non-respiratory toxicity, non-sensitivity to the skin, non-hepatotoxic, and don't have toxicity on minnow toxicity and T. pyriformis indicating a good toxicity profile for human.

Biosynthesized silver nanoparticles (Ag NPs) from isolated actinomycetes strains and their impact on the black cutworm, Agrotis ipsilon.

Nanomaterials have been produced with the use of bio-nanotechnology, which is a low-cost approach. Currently, research is being conducted to determine whether actinomycetes isolated from Egyptian soil can biosynthesize Ag nanoparticles (Ag NPs) and characterized by using the following techniques: Transmission electron microscopy (TEM), Dynamic light scattering (DLS), Fourier transforms infrared (FT-IR), Energy-dispersive X-ray spectroscopy (EDX), UV-Vis spectroscopy and X-ray diffraction (XRD). The most promising actinomycetes isolate were identified, morphologically, biochemically, and molecularly. Streptomyces avermitilis Azhar A.4 was found to be able to reduce silver metal nanoparticles from silver nitrate in nine isolates collected from Egyptian soil. Toxicity of biosynthesized against 2nd and 4th larval instar of Agrotis ipsilon (Hufn.) (Lepidoptera: Noctuidae) was estimated. In addition, activity of certain vital antioxidant and detoxifying enzymes as well as midgut histology of treated larvae were also investigated. The results showed appositive correlations between larval mortality percentage (y) and bio-AgNPs concentrations (x) with excellent (R2). The 4th larval instar was more susceptible than 2nd larval instar with LC50 (with 95% confirmed limits) =8.61 (2.76-13.89) and 26.44(13.25-35.58) ppml-1, respectively of 5 days from treatment. The initial stages of biosynthesized AgNps exposure showed significant increases in carboxylesterase (CarE) and peroxidases (PODs) activity followed by significant suppression after 5 days pos-exposure. While protease activity was significantly decreased by increasing time post-exposure. Midgut histology showed abnormality and progressive damage by increasing time post exposure leading to complete destruction of midgut cells after 5 days from exposure. These results make biosynthesized AgNPs an appropriate alternative to chemical insecticide in A. ipsilon management.

Effectiveness and biochemical impact of ozone gas and silica nanoparticles on Culex pipiens (Diptera: Culicidae).

Culex pipiens (Diptera: Culicidae) is a vector of many serious human diseases, and its control by the heavy use of chemical insecticides has led to the evolution of insecticide resistance and high environmental risks. Many safe alternatives, such as ozone gas (O3) and silica nanoparticles (silica NPs) can reduce these risks. Therefore, O3 and silica NPs were applied to 3rd larval instars of Cx. pipiens at different concentrations (100, 200, and 400 ppm) for different exposure times (1, 2, 3, and 5 min for O3 and 24, 48, and 72 h for silica NPs). The activity of some vital antioxidant enzymes as well as scanning electron microscopy of the body surface were also investigated. A positive correlation was observed between larval mortality % and the tested concentrations of O3 and silica NPs. O3 was more effective than silica NPs, it resulted in 92% mortality at 400 ppm for a short exposure time (5 min). O3-exposed larvae exhibited a significant increase in glutathione peroxidase, glutathione S-transferase, and catalase activities as well as the total antioxidant capacity. Scanning electron microscopy showing disruptive effects on the body surface morphology of ozone and silica NPs treated larvae. These results provide evidence that O3 and silica NPs have the potential for use as alternative vector control tools against Cx. pipiens.