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The cytotoxicity and genotoxicity of abamectin, chlorfenapyr, and imidacloprid have been evaluated on the Chinese hamster ovary (CHOK1) cells. Neutral red incorporation (NRI), total cellular protein content (TCP), and methyl tetrazolium (MTT) assays were followed to estimate the mid-point cytotoxicity values, NRI50, TCP50, and MTT50, respectively. The effects of the sublethal concentration (NRI25) on glutathione S-transferase (GST), glutathione reductase (GRD), glutathione peroxidase (GPX), and total glutathione content have been evaluated in the presence and absence of reduced glutathione (GSH), vitamin C, and vitamin E. The genotoxicity was evaluated using chromosomal aberrations (CA), micronucleus (MN) formation, and DNA fragmentation techniques in the presence and absence of the metabolic activation system, S9 mix. Abamectin was the most cytotoxic pesticide followed by chlorfenapyr, while imidacloprid was the least cytotoxic one. The glutathione redox cycle components were altered by the tested pesticides in the absence and presence of the tested antioxidants. The results of genotoxicity indicate that abamectin, chlorfenapyr, and imidacloprid have potential genotoxic effects on CHOK1 cells under the experimental conditions.

Plants are a prospective source of novel natural insect repellents and botanical insecticides. This study was conducted to investigate the chemical composition of the essential oils of three plants growing in Saudi Arabia, namely Ducrosia anethifolia, Achillea fragrantissima, and Teucrium polium; and to evaluate their potential mosquitocidal and repellent activities against adult female Culex pipiens L. The main components of the three oils were found to be decanal (28.9%) and chrysanthenyl acetate (10.04%), (D. anethifolia); sabinyl acetate (35.79) and artemesia ketone (18.28%) (A. fragrantissima); α‐cadinol (49.53%) and δ‐cadinene (10.23%) (T. polium). The oil of A. fragrantissima was the most toxic (LC50 = 0.11 μL/L air) followed by D. anethifolia and T. polium with LC50 values of 5.22 and 25.98 μL/L air, respectively. T. polium oil was the most repellent (292 min at 2 μL/cm2), followed by D. anethifolia and A. fragrantissima. The results indicate that the essential oils have a potential fumigant insecticidal and repellent activities for mosquito control.

The development of resistance to an insecticide under various types of application method has yet to be reported in the literature. Five fall armyworm Spodoptera armigera (JE Smith) colonies were reared in a chamber for ten generations before starting topical application bioassays. From each colony, 200-500 third-fourth-instar larvae were fed for 72 h on corn plants sprayed with cypermethrin or spinosad at minimum application rate (20 g ha(-1)) using a small droplet size nozzle XR8001VS (volume median diameter D(v0.5) = 163 microm) or a large droplet size nozzle XR8008VS (D(v0.5) = 519 microm). Surviving larvae were transferred to untreated corn leaves to complete their life cycle. Next-generation third-instar larvae of each colony were topically dosed with technical cypermethrin or spinosad at 1 microL per larva, and mortality was recorded 24 h post-treatment. The results indicated that cypermethrin demonstrated an insecticidal activity greater than that of spinosad, and the cypermethrin regression lines moved to the right faster than those for spinosad, indicating an increased tolerance of cypermethrin. Generally, larvae from all generations (F1-F7) under the XR8008VS treatments were less susceptible to cypermethrin and developed resistance faster and to higher levels than larvae from the XR8001VS treatments. The confidence limits (95%) of LD(50) for all spinosad treatments indicated that there was no significant difference from the LD(50) value of the susceptible reference strain. The results are a first indication that application technology/insecticide reaction may affect the rapidity of resistance development in certain pest/plant scenarios, but field studies are needed to confirm this conclusion.

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