Cotton leafworm, Spodoptera littoralis (Boisd.) is a key pest affecting many field crops and vegetables in Egypt. Therefore, in the current study, the susceptibility of the 2nd instar larvae of S. littoralis laboratory strain to eight insecticides was investigated and the insecticide resistance levels of two field populations were monitored. The two populations were collected from two governorates in Egypt, namely El-Monufia (MS) and El-Fayoum (FS). Resistance monitoring showed that the field population from El-Fayoum was highly resistant to chlorantraniliprole, emamectin benzoate (EMB), spinotram, and spinosad. However, the El-Monufia field population only exhibited high resistance to chlorantraniliprole and spinosad. The relative toxicity showed that the laboratory strain is highly sensitive to EMB (LC50= 0.001 ppm) followed by spinotram (LC50= 0.006 ppm), chlorantraniliprole (LC50= 0.008 ppm), spinosad (LC50= 0.008 ppm), and indoxacarb (LC50= 0.021 ppm), while chlorfenapyr, fipronil, and alpha-cypermethrin exhibited low toxicity to the laboratory strain of S. littoralis. Moreover, the biochemical determinations of detoxification enzymes revealed that carboxylesterase (α, and β -esterase), and AChE activity were significantly increased in the FS population. Thus, Glutathione S-Transferase (GST) showed significant increase in the two populations.

Methoxyfenozide (M) is one of the selective insecticides used in integrated pest management (IPM) programs for lepidopteran pests. However, recent studies reported a development of M-resistance, which prompted us to look for alternatives. Here, we investigate the potency of a mixture of M with spinetoram (Sp) on M-resistant insects. In the laboratory, a selection pressure with M has carried out on Spodoptera littoralis (Lepidoptera: Noctuidae) strains. A dipping technique was used to evaluate the toxicity of a sublethal concentration of M and Sp. on S. littoralis larvae, and the same concentrations were used to assess the toxic impact of their combination on susceptible (SUS) and M-selected (MS) strains. The toxicity of M/Sp mixtures was computed using a combination index equation, and a potentiation effect was observed in the two tested strains. Synergism tests revealed that piperonyl butoxide had considerable synergistic effects on M toxicity in the MS strain. The results revealed that the M/Sp mixture's negative effect on both monooxygenases and esterases is most likely the cause of its potentiation effect on the SUS and MS strains. It was concluded that M/Sp mixtures are effective against M-resistant S. littoralis strains, so these can be used in IPM programs.

Reducing nematicide dose rates could be a useful strategy for mitigating their negative effects on health and the environment. In this study, enzymatic activities and the parasitic ability of Meloidogyne incognita after exposure to sub-lethal concentrations (0.25, 1, 2, and 5 ppm) of ethoprophos, fenamiphos, and oxamyl were investigated. Although the tested concentrations did not show nematicidal properties in vitro, they reduced root galls by at least 30% at 0.25 ppm and up to 67% at 5 ppm in pots, besides disrupting nematode fertility. For all three nematicides at 2 ppm, a chemotaxis assay showed that ≤ 11% of the nematode population was successfully oriented to the host roots, compared to 44% in the control. Ethoprophos and fenamiphos at 5 ppm showed poor inhibitory effects on acetylcholinesterase (AChE) activity (5.6% and 12.5%, respectively). In contrast, the same nematicides were shown to be strong ATPase inhibitors, causing 82.4% and 82.8% inhibition, respectively. At the same concentration, oxamyl moderately inhibited AChE and ATPase-specific activities, the inhibition being 22.5% and 35.2%, respectively. This study suggests that the use of very low nematicide concentrations could be a promising strategy for nematode management. Furthermore, it has also highlighted the role of ATPases as a possible target site for suppressing nematode activity in the development of future nematicides.

In this study, in vitro and in silico approaches were employed to assess the toxicity of marjoram (Origanum majorana) and rosemary (Rosmarinus officinalis) essential oils (EOs) to A. ipsilon larvae. The study determined the activities of ATPases in the larvae after treatment with the LC₂₀ and LC₇₀ of each EO. α-esterase and glutathione-S-transferase (GST) activities were also determined after treatment with LC₁₀ and LC₃₀ of each EO. Furthermore, molecular docking was employed to determine the binding affinity of terpinene-4-ol and α-pinene, the major constituents of O. majorana, and R. officinalis EOs, respectively, compared to the co-crystallized ligand of α-esterase, diethyl hydrogen phosphate (DPF). Toxicity assays revealed that O. majorana EO was more toxic than R. officinalis EO to the A. ipsilon larvae at 96 h post-treatment. However, the LC₂₀ and LC₇₀ of the latter significantly inhibited the activity of the Na⁺-K⁺ pump at almost all intervals. The same concentrations significantly inhibited the Mg²⁺/Ca²⁺-ATPase and Ca²⁺ pump at 96 h post-treatment. In contrast, O. majorana EO showed a variable effect on the Na+-K+ pump across different time intervals. On the other hand, LC₁₀ and LC₃₀ of both EOs showed varied effects on α-esterase and GST over time. Molecular docking revealed energy scores of −4.51 and −4.29 kcal/mol for terpinene-4-ol and α-pinene, respectively, compared to a score of −4.67 for PDF. Our study demonstrated the toxicity of the tested EOs to A. ipsilon, suggesting their potential efficacy as insecticides.

The use of essential oils as an eco-friendly tool in pest management stems from their natural origin and the presence of bioactive compounds that exhibit pesticidal properties, offering a sustainable alternative to synthetic chemical pesticides. This study explores the toxicity of Lavandula multifida (lavender) essential oil (EO), as a botanical pesticide against two widespread and destructive Noctuidae pests, Spodoptera littoralis (Boisd.) and Agrotis ipsilon (Hufnagel). GC-MS was employed to characterize 23 compounds in the EO, with 1,3,3-trimethyl-2-oxabicyclo [2.2.2] octane (eucalyptol) (39.84%), being the primary component. The leaf dipping technique was utilized to assess the toxicity of the EO to both insects. At 96 hours post-treatment, the LC50 of lavender EO to S. littoralis and A. ipsilon larvae were 2.350 and 2.991 mg · ml–1, respectively. Concerning its biological effect, both concentrations of the EO (LC15 and LC50) significantly shortened the duration of the larval (to 15.24 and 14.23 days) and pupal (to 11.19 and 10.55 days) stages of S. littoralis. Biochemical assays revealed that the LC50 of lavender EO significantly inhibited α-esterase activity in S. littoralis at 72- and 96 hours post-treatment (0.031 and 0.063 mmol · min–1 · mg–1), and A. ipsilon at 96 hours post-treatment (0.129 mmol · min–1 · mg–1 protein). Given its significant toxicological, biological, and biochemical effects on S. littoralis, it is suggested that lavender EO could be considered for use in integrated pest management strategies while ensuring its safe application to protect non-target organisms.